This document was updated in December 2019. Please consult the website for any
content updates (http://www.who.int/malaria)
WHO malaria
terminology
Global Malaria Programme
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Table of contents
Acknowledgements 3
Introduction 4
Process 4
The special case of “malaria case” 6
Glossary 8
Bibliography
28
Archived terms
30
2
DRAFTING COMMITTEE
Members
Professor Andrei Beljaev Russian Academy of Postgraduate Medical Training,
Moscow, Russian Federation
Professor Graham Brown Nossal Institute for Global Health, University of
Melbourne, Australia
Dr Kamini Mendis Independent Expert, Colombo, Sri Lanka
Dr José Najera Independent Expert, Crans de Celigny, Switzerland
Dr Trenton Ruebush Independent Expert, Alexandria, Virginia, USA
Dr Rick Steketee Malaria Control and Elimination Programme,
(Chairperson) PATH, Seattle, Washington, USA
Professor Graham White Entomology and Nematology Department, University of
Florida, Gainesville, Florida, USA
WHO Secretariat
Dr Pedro Alonso Director, Global Malaria Programme
Dr Andrea Bosman Coordinator, Prevention Diagnostics and Treatment,
Global Malaria Programme
WHO MALARIA TERMINOLOGY
3
ACKNOWLEDGEMENTS
The invaluable support provided by Ms Mar Velarde, ISGlobal, Malaria Eradication
Scientific Alliance, in the desk review for the drafting committee is gratefully
acknowledged. The contributions of all members of the drafting committee are
recognized. Their precision, careful attention and timely, precious feedback were
instrumental for completion of the work. The external survey was ably managed by
Mr Ryan Williams, WHO Global Malaria Programme, following the indications of
the drafting committee, and all inputs and the analysis of the survey results were
eciently compiled by Ms Silvia Schwarte, WHO Global Malaria Programme. The
inputs received from over 20 institutions and groups are greatly appreciated. These
included the Asia–Pacific Malaria Elimination Network; the Foundation for Innovative
New Diagnostics; the Gates Foundation malaria programme; IVCC (Liverpool School
of Tropical Medicine); the Malaria Elimination Group, University of California, San
Francisco; Medicines for Malaria Venture; PATH Malaria Control and Elimination
Partnership in Africa; the Centers for Disease Control and Prevention (USA); and
the President’s Malaria Initiative (USA). Support was also provided by the Roll Back
Malaria (RBM) Case Management Working Group, the RBM Monitoring Evaluation
Reference Group, the RBM Vector Control Working Group, the Vector Control Advisory
Group (WHO Global Malaria Programme), WHO regional malaria advisers and the
WHO Technical Expert Groups on Antimalarial Drug Resistance and Containment,
Malaria Chemotherapy, Surveillance, Monitoring and Evaluation and Vector Control.
Input is also acknowledged from numerous WHO collaborating centres, for: Malaria;
Surveillance of Antimalarial Drug Resistance; Evaluation of New Insecticides against
Vectors; Ecology, Taxonomy and Control of Vectors of Malaria, Filariasis and Dengue;
Malaria Diagnosis; Malaria Control, Elimination and Eradication; Clinical Management
of Malaria; Geospatial Disease Modelling; Prevention and Control of Malaria; and
Early Warning Systems for Malaria and Other Climate-sensitive Diseases. Dr Rick
Steketee, Chairperson of the Drafting Committee provided guidance throughout the
planning and review process, and Dr Andrea Bosman served as the secretariat of the
committee. The work was funded as part of a contribution from the Bill & Melinda
Gates Foundation to the WHO Global Malaria Programme.
4
In recent years, there has been a proliferation of new terms in relation to malaria in
the scientific literature, the media and technical reports and also of terms with new
or modified use and meaning. These changes stem from renewed global interest
in malaria elimination and eradication, increasing access to scientific and technical
information and faster translation of research findings into evidence-based policies.
This proliferation has raised certain diculties:
• Some new terms are used in several dierent ways.
• Several similar terms have the same meaning.
• Some terms used to describe malaria interventions have dierent meanings in
other public health programmes.
The situation is generating increasing confusion and misunderstanding, not only
in the scientific community and funding agencies but also among public health
ocials responsible for malaria programmes and policy-makers in malaria-endemic
countries. WHO has periodically reviewed the terminology of malaria; however, the
latest ocial publication on this topic dates back to 1963.
1
Several WHO publications
in the past 10 years have included glossaries of terms used in malaria surveillance,
control and elimination; however, there has been no comprehensive review of the
terminology of malaria since the work of the drafting committee in 1963.
On this basis and on the advice of the Malaria Policy Advisory Committee at its seventh
biannual meeting in March 2015, the WHO Global Malaria Programme Secretariat
decided to update the WHO terminology of malaria as a glossary.
PROCESS
First, a desk review was conducted of terms used in programmes for malaria
elimination and eradication that have dierent definitions and uses. The glossaries
and lists of terms and definitions reviewed were those in:
• all WHO publications on malaria since 1995, in addition to those in Terminology of
malaria and of malaria eradication
1
(16 documents);
Introduction
Medical language must be adaptable so that it
can keep pace with the constant increase of our
knowledge and with the continual revision and
evolution of our concepts.
Terminology of malaria and of malaria eradication. WHO; 1963
WHO MALARIA TERMINOLOGY
5
• publications by other WHO departments, such as “preventive chemotherapy for
neglected tropical diseases” (16 documents); and
• scientific papers with definitions or glossary published during the past 10 years, to
identify terms used recurrently that are the same or similar but are given dierent
meanings and also new terms that are given similar meanings (15 publications).
The search revealed 292 terms, which were divided into four groups: elimination
(50), vector control (69), surveillance (85) and diagnosis and treatment (88); many
terms were relevant to both elimination and surveillance. Initial draft definitions were
proposed for each term.
All 292 terms and their definitions were submitted for discussion to the members of the
newly formed Drafting Committee on Malaria Terminology, who were asked to classify
them into three groups:
• those that were and are still relevant and properly described, to be reviewed to
update the language but generally considered “good as they stand”;
• those that have been used in the past and have value for historical purposes but
are no longer in current use and could be considered for archiving; and
• terms that are relevant today but have taken on a new meaning or dierent use,
which should be reviewed and possibly redefined or at least updated so that the
definition reflects their current use.
After the initial individual reviews, the Committee was convened for a consultation
in Geneva on 2–3 June 2015, where the members worked in pairs on all terms and
presented the results in plenary for review by the whole committee. The work was
refined after the meeting, through e-mail exchanges among Committee members,
when a concerted eort was made to simplify the definitions as much as possible.
As a result, the recommended definitions tended to be short, and explanatory notes
were added. After this extensive work, the Drafting Committee considered that 153
terms were properly described, proposed 38 for archiving and identified 101 terms as
requiring additional work.
For the 101 terms requiring additional work and external review, WHO set up an online
survey to collect expert feedback in a systematic way. A web link was issued to 30
identified institutions or groups (full list in the Acknowledgements), and 47 passcodes
(“tokens”) dedicated to institutions or groups were sent to the corresponding lead
contacts (e.g. chief executive ocers, chairs or co-chairs of working groups and
directors), who could recruit additional technical resources from their institution
or group to participate in the review by sharing the passcode. The input from the
reviewers at each institution or group was recorded as a single response with a single
token. To facilitate review and feedback, the 101 terms were grouped into four thematic
areas: diagnosis and treatment (32 terms), elimination (28 terms), surveillance
(21 terms) and vector control (20 terms). Each term had a draft definition and, when
appropriate, an explanatory note. For each term and commentary, the reviewer was
invited to recommend: retain (“OK”), reject (“omit”) or amend (“modify”) with a written
alternative text.
The survey was carried out between 6 and 26 July 2015. Responses were obtained with
25/47 tokens from 20/30 institutions or groups. A total of 1260 entries were received.
The external reviewers found that 884 entries were acceptable, recommended 75
entries for archiving and recommended specific modifications for 301 terms. Only five
6
terms were marked “OK” by all reviewers: causal prophylaxis, passive case detection,
stable transmission, unstable transmission and gonotrophic dissociation.
All inputs were reviewed and compiled by the WHO Global Malaria Programme
Secretariat, and the suggested modifications were then submitted to the Drafting
Committee for review by e-mail exchange. The consolidated result of this work, in
the form of a glossary, was then submitted for final discussion to the Malaria Policy
Advisory Committee at its eighth biannual meeting in September 2015. The Committee
also discussed the term “malaria case”, which had generated significant debate
among the members of the Drafting Committee and external reviewers.
The list of terms and definitions resulting from this process is presented in the glossary
below, which is posted online on WHO website. It will be updated regularly on the
basis of input from WHO technical expert groups and review by the WHO Drafting
Committee on Malaria Terminology.
THE SPECIAL CASE OF “MALARIA CASE”
The most dicult definition for review was that of a “malaria case”. The complexity of
defining this term was already recognized when the first WHO terminology for malaria
and malaria eradication
1
was published. In that publication, a case was defined as
follows:
Case. An occurrence or instance of infection or disease. The word is so
vague that the type of case should always be specified, as, for instance, a
malaria case or a fever case.
“Case” is defined generally in Dorland’s medical dictionary
2
as follows:
Case. A particular instance of disease; sometimes used incorrectly to
designate the patient with the disease
Malaria control programmes typically report the number of “malaria cases” as the
number of people presenting with illness diagnosed as malaria infection, consistent
with the above definition of an instance of illness or disease linked to infection.
With the transition of a malaria programme to elimination, emphasis is shifted to
malaria infections that may remain asymptomatic for long periods and contribute to
transmission. In the elimination phase, therefore, the term “malaria case” evolves to
apply to both symptomatic and asymptomatic infections.
In the current recommendation for parasitological confirmation of malaria when an
individual presents with illness that is suspected to be malaria, WHO recommends that
all “cases” be confirmed with the available diagnostic tools.
As there was no unanimous agreement on the definition or on a proposal to modify
the definition of “case” for the transition from control to elimination, the Drafting
Committee decided to propose two options to a wider audience to obtain additional
comment:
WHO MALARIA TERMINOLOGY
7
Draft definition 1: Occurrence of malaria illness or disease in a person in
whom the presence of malaria parasites in the blood has been confirmed
by parasitological testing.
Note: A malaria case can be classified as suspected, presumed or
confirmed and as autochthonous, indigenous, induced, introduced or
imported (depending on the origin of infection) or as relapsing.
Draft definition 2: Occurrence of malaria infection (symptomatic or
asymptomatic) in a person in whom the presence of parasites in the blood
has been confirmed by parasitological testing.
Note: A malaria case can be classified as autochthonous, indigenous,
induced, introduced or imported (depending on the origin of infection) or
as relapsing.
The results of the external survey, additional review by the Drafting Committee and
the advice of the Malaria Policy Advisory Committee showed general consensus for
a single definition of “malaria case”, as proposed in this glossary, for surveillance
purposes, which would be applicable to various areas in countries, including those for
malaria elimination. The definition proposed below reflects the action required for
malaria elimination, which is increasingly the aims of all malaria programmes within
the Global Technical Strategy for Malaria: 2016–2030.
3
It has already been adopted
and is in widespread use in malaria elimination programmes, with related terms (e.g.
“case investigation”, “index case”, “case follow-up”). It is in line with the requirement
that countries report only laboratory-confirmed cases as “malaria cases” and has the
advantage of continuity with the definition of the past.
Malaria case. Occurrence of malaria infection in a person in whom the
presence of malaria parasites in the blood has been confirmed by a
diagnostic test
Note: A suspected malaria case cannot be considered a malaria case until
parasitological confirmation. A malaria case can be classified as imported,
indigenous, induced, introduced, relapsing or recrudescent (depending
on the origin of infection); and as symptomatic or asymptomatic. In
malaria control settings, a “case” is the occurrence of confirmed malaria
infection with illness or disease. In settings where malaria is actively being
eliminated or has been eliminated, a “case” is the occurrence of any
confirmed malaria infection with or without symptoms.
There is strong consensus that, to reduce confusion, all malaria data sets should
include the malaria case definition.
References
1. Terminology of malaria and of malaria eradication: report of a drafting committee.
Geneva, World Health Organization; 1963 (https://extranet.who.int/iris/restricted/
bitstream/10665/39007/1/9241540141_eng.pdf).
2. Dorland’s Illustrated Medical Dictionary. Philadelphia: Elsevier Saunders; 2012.
3. Global Technical Strategy for Malaria 2016–2030. Geneva: World Health Organization; 2015.
8
adherence Compliance with a regimen (chemoprophylaxis or treatment) or with
procedures and practices prescribed by a health care worker
adverse drug reaction A response to a medicine that is harmful and unintended and which
occurs at doses normally used in humans
adverse event Any untoward medical occurrence in a person exposed to a biological
or chemical product, which does not necessarily have a causal
relationship with the product
Note: During malaria interventions, adverse events may be reported
following treatment with anti malarial medicines and/or exposure
to insecticides. The standard definition in the good clinical practice
guidelines of the International Conference on Harmonisation of
Technical Requirements for Registration of Pharmaceuticals for Human
Use refers to pharmaceutical products only.
adverse event, serious Any untoward medical occurrence in a person exposed to a biological
or chemical product, which is not necessarily causally related to the
product, and results in death, requirement for or prolongation of
inpatient hospitalization, significant disability or incapacity or is life-
threatening
aestivation A process by which mosquitoes at one or several stages (eggs, larvae,
pupae, adults) survive by means of behavioural and physiological
changes during periods of drought or high temperature
age group Subgroup of a population classified by age. The following grouping is
usually recommended:
• 0–11 months
• 12–23 months
• 2–4 years
• 5–9 years
• 10–14 years
• 15–19 years
• ≥ 20 years
Note: Reporting on age groups can be modified, as appropriate, to local
transmission, whereby certain age groups may be of specific interest (e.g.
for passive immunity or assessment of ongoing transmission, 0–5 months
and 6–11 months; young migrant work force, ≥ 20–29 years; elderly > 60
years, because of the risk for complications).
age, physiological Adult female mosquito age in terms of the number of gonotrophic
cycles completed: nulliparous, primiparous, 2-parous, 3-parous et seq.
Note: Vector age is typically assessed by age grading instead of days.
age-grading, of female
adult mosquitoes
Classification of female mosquitoes according to their physiological
age (number of gonotrophic cycles) or simply as nulliparous or parous
(parity rate)
Note: Vectors are age-graded mainly to assess the impact of
environmental changes (natural or intended for control) on vector
populations. In epidemiological studies, age-grading of vectors is used
to estimate the mean probability of their survival, a key variable for
calculating the basic reproduction number, R
0
, and vectorial capacity.
Glossary
WHO MALARIA TERMINOLOGY
9
age-grading, of
mosquito larvae
Classification of mosquito larvae as instars (development stages) 1, 2,
3 and 4
annual blood
examination rate
The number of people receiving a parasitological test for malaria per
unit population per year
Anopheles, infected Female Anopheles mosquitoes with detectable malaria parasites
Anopheles, infective Female Anopheles mosquitoes with sporozoites in the salivary glands
anopheline density Number of female anopheline mosquitoes in relation to the number of
specified shelters or hosts (e.g. per room, per trap or per person) or to
a given period (e.g. overnight or per hour), specifying the method of
collection
Note: This term refers strictly to the population density or abundance of
adult female Anopheles mosquitoes. Anopheline mosquito density is a
highly insensitive measure of malaria transmission.
anthropophilic Description of mosquitoes that show a preference for feeding on
humans, even when non-human hosts are available
Note: A relative term requiring quantification to indicate the extent of
preference for anthropophily versus zoophily; usually expressed as the
human blood index (proportion of mosquitoes that have fed on humans
out of total fed)
antimalarial medicine A pharmaceutical product used in humans for the prevention,
treatment or reduction of transmission of malaria
artemisinin-based
combination therapy
A combination of an artemisinin derivative with a longer-acting
antimalarial drug that has a dierent mode of action
basic reproduction
number
The number of secondary cases that a single infection (index case)
would generate in a completely susceptible population (referred to as
R
0
)
Note: The “adjusted reproduction number”, R
c
, is the reproduction number
in the presence of a range of interventions, e.g. insecticide-treated nets,
indoor residual spraying and access to treatment.
bioassay In applied entomology, experimental testing of the biological
eectiveness of a treatment (e.g. infection, insecticide, pathogen,
predator, repellent) by deliberately exposing insects to it
Note: When bioassays are used for periodic monitoring of the continued
ecacy of residual insecticide deposits on sprayed surfaces in houses (as
in indoor residual spraying), attention should be paid to the environmental
conditions and possible adverse factors (e.g. washing, re-plastering, soot)
that aect the deposits on treated surfaces; these factors may reduce the
eectiveness of treatment dierently from the intrinsic rate of decay of the
insecticide.
biting rate Average number of mosquito bites received by a host in a unit time,
specified according to host and mosquito species (usually measured
by human landing collection)
Note: Human malariology mainly requires the “human biting rate” of
vectors.
capture site Site selected for periodic sampling of the mosquito population of a
locality for various purposes
10
case, confirmed Malaria case (or infection) in which the parasite has been detected
in a diagnostic test, i.e. microscopy, a rapid diagnostic test or a
molecular diagnostic test
Note: On rare occasions, the presence of occult malaria infection in a
blood or organ donor is confirmed retrospectively by the demonstration of
malaria parasites in the recipient of the blood or organ.
case, fever The occurrence of fever (current or recent) in a person
Note: Fever is often used as a screening criterion before performing a
diagnostic test to detect malaria.
case, imported Malaria case or infection in which the infection was acquired outside
the area in which it is diagnosed
case, index A case of which the epidemiological characteristics trigger additional
active case or infection detection. The term “index case” is also used
to designate the case identified as the origin of infection of one or a
number of introduced cases.
case, indigenous A case contracted locally with no evidence of importation and no
direct link to transmission from an imported case
case, induced A case the origin of which can be traced to a blood transfusion
or other form of parenteral inoculation of the parasite but not to
transmission by a natural mosquito-borne inoculation
Note: in controlled human malaria infections in malaria research, the
parasite infection (challenge) may originate from inoculated sporozoites,
blood or infected mosquitoes.
case, introduced A case contracted locally, with strong epidemiological evidence
linking it directly to a known imported case (first-generation local
transmission)
case, locally acquired A case acquired locally by mosquito-borne transmission
Note: Locally acquired cases can be indigenous, introduced, relapsing or
recrudescent; the term “autochthonous” is not commonly used.
case, malaria Occurrence of malaria infection in a person in whom the presence of
malaria parasites in the blood has been confirmed by a diagnostic test
Note: A suspected malaria case cannot be considered a malaria case
until parasitological confirmation. A malaria case can be classified as
imported, indigenous, induced, introduced, relapsing or recrudescent
(depending on the origin of infection); and as symptomatic or
asymptomatic. In malaria control settings, a “case” is the occurrence
of confirmed malaria infection with illness or disease. In settings where
malaria is actively being eliminated or has been eliminated, a “case” is the
occurrence of any confirmed malaria infection with or without symptoms.
For more discussion on “malaria case”, see the section on “The special case
of malaria case”, above.
case, presumed Case suspected of being malaria that is not confirmed by a diagnostic
test
Note: The designation “presumed case” is reserved for uncommon
situations in which a diagnostic test cannot be performed in a timely
manner.
case, recrudescent Malaria case attributed to the recurrence of asexual parasitemia
after antimalarial treatment, due to incomplete clearance of asexual
parasitemia of the same genotype(s) that caused the original illness.
A recrudescent case must be distinguished from reinfection and relapse,
in case of P. vivax and P. ovale.
WHO MALARIA TERMINOLOGY
11
case, relapsing Malaria case attributed to activation of hypnozoites of P. vivax or
P. ovale acquired previously
Note: The latency of a relapsing case can be > 6–12 months. The
occurrence of relapsing cases is not an indication of operational failure,
but their existence should lead to evaluation of the possibility of ongoing
transmission.
case, suspected
malaria
Illness suspected by a health worker to be due to malaria, generally on
the basis of the presence of fever with or without other symptoms
case detection One of the activities of surveillance operations, involving a search for
malaria cases in a community
Note: Case detection is a screening process in which the indicator is either
the presence of fever or epidemiological attributes such as high-risk
situations or groups. Infection detection requires use of a diagnostic test to
identify asymptomatic malaria infections.
case detection, active Detection by health workers of malaria cases at community and
household levels, sometimes in population groups that are considered
at high risk. Active case detection can consist of screening for fever
followed by parasitological examination of all febrile patients or as
parasitological examination of the target population without prior
screening for fever.
Note: Active case detection may be undertaken in response to a confirmed
case or cluster of cases, in which a population potentially linked to such
cases is screened and tested (referred to as “reactive case detection”), or
it may be undertaken in high-risk groups, not prompted by detection of
cases (referred to as “proactive case detection”).
case detection, passive Detection of malaria cases among patients who, on their own
initiative, visit health services for diagnosis and treatment, usually for a
febrile illness
case follow-up Periodic re-examination of patients with malaria (with or without
treatment)
Note: Follow-up may involve blood examination and treatment if the
patient did not respond to previous medicines. Case follow-up is part of
surveillance.
case investigation Collection of information to allow classification of a malaria case by
origin of infection, i.e. imported, indigenous, induced, introduced,
relapsing or recrudescent
Note: Case investigation may include administration of a standardized
questionnaire to a person in whom a malaria infection is diagnosed
and screening and testing of people living in the same household or
surrounding areas.
case management Diagnosis, treatment, clinical care, counselling and follow-up of
symptomatic malaria infections
case notification Compulsory reporting of all malaria cases by medical units and
medical practitioners to either the health department or the malaria
control programme, as prescribed by national laws or regulations
catchment area A geographical area defined and served by a health programme or
institution, such as a hospital or community health centre, which is
delineated on the basis of population distribution, natural boundaries
and accessibility by transport
12
cerebral malaria Severe P. falciparum malaria with impaired consciousness (Glasgow
coma scale < 11, Blantyre coma scale < 3) persisting for > 1 hour after
a seizure
Note: The initial neurological symptoms are often drowsiness, confusion,
failure to eat or drink or convulsions (see current WHO definition of severe
malaria in the Guidelines for the treatment of malaria. 2015, Third edition).
certification of
malaria-free status
Certification granted by WHO after it has been proved beyond
reasonable doubt that local human malaria transmission by
Anopheles mosquitoes has been interrupted in an entire country for
at least 3 consecutive years and a national surveillance system and a
programme for the prevention of reintroduction are in place
chemoprevention,
seasonal malaria
Intermittent administration of full treatment courses of an antimalarial
medicine during the malaria season to prevent malarial illness. The
objective is to maintain therapeutic concentrations of an antimalarial
drug in the blood throughout the period of greatest risk for malaria.
Note: This intervention is recommended only for areas with highly seasonal
malaria, where transmission occurs during a few months of the year.
chemoprophylaxis Administration of a medicine, at predefined intervals, to prevent either
the development of an infection or progression of an infection to
manifest disease
cluster Aggregation of relatively uncommon events or diseases in space
and/or time in numbers that are considered greater than could be
expected by chance
combination therapy A combination of two or more classes of antimalarial medicine with
unrelated mechanisms of action
coverage A general term referring to the fraction of the population of a specific
area that receives a particular intervention
coverage, universal Access to and use of appropriate interventions by the entire population
at risk of malaria
cure Elimination from an infected person of all malaria parasites that
caused the infection
Note: When applied to P. vivax and P. ovale malaria, the term is equivalent
to radical cure.
cure, radical Elimination of both blood-stage and latent liver infection in cases of P.
vivax and P. ovale infection, thereby preventing relapses
Note: The term is used only for P. vivax and P. ovale infections, to reflect
the use of anti-hypnozoite medicines.
cure rate Percentage of treated individuals whose infection is cured
cyto-adherence Propensity of malaria-infected erythrocytes to adhere to the
endothelium of the micro vasculature of the internal organs of the host
diagnosis The process of establishing the cause of an illness (for example, a
febrile episode), including both clinical assessment and diagnostic
testing
diagnosis, molecular Use of nucleic acid amplification-based tests to detect the presence of
malaria parasites
WHO MALARIA TERMINOLOGY
13
diagnosis,
parasitological
Diagnosis of malaria by detection of malaria parasites or
Plasmodium-specific antigens or genes in the blood of an infected
individual
diapause Condition of suspended animation or temporary arrest in the
development of immature and adult mosquitoes
dosage regimen (or
treatment regimen)
Prescribed formulation, route of administration, dose, dosing interval
and duration of treatment with a medicine
dose
Quantity of a medicine to be taken at one time or within a given period
Note: The quantities of antimalarial medicines should be expressed as
base (when applicable) and fractions of a gram or milligrams.
dose, loading One or a series of doses that may be given at the start of therapy with
the aim of achieving the target concentration rapidly
drug ecacy Capacity of an antimalarial medicine to achieve the therapeutic
objective when administered at a recommended dose, which is well
tolerated and has minimal toxicity
drug resistance The ability of a parasite strain to survive and/or multiply despite the
absorption of a medicine given in doses equal to or higher than those
usually recommended
Note: Drug resistance arises as result of genetic changes (mutations or
gene amplification) that confer reduced susceptibility
drug safety (See Medicine safety)
drug, gametocidal A drug that kills male and/or female gametocytes, thus preventing
them from infecting a mosquito
drug, schizontocidal A drug that kills schizonts, either in the liver or the blood
endemic area An area in which there is an ongoing, measurable incidence of
malaria infection and mosquito-borne transmission over a succession
of years
endemicity, level of
Degree of malaria transmission in an area
Note: Various terms have been used to designate levels of endemicity, but
none is fully satisfactory. Parasite rate or spleen rate has been used to
define levels of endemicity in children aged 2–9 years, i.e. hypoendemic:
0–10%; mesoendemic: 10–50%, hyperendemic: constantly > 50% and
holoendemic: constantly ≥ 75% with a low adult spleen rate Parasite
density decreases rapidly between 2 and 5 years of age.
endophagy
Tendency of mosquitoes to blood-feed indoors
Note: Contrasts with exophagy
endophily Tendency of mosquitoes to rest indoors.
Note: Contrasts with exophily; usually quantified as the proportion resting
indoors; used in assessing the eect of indoor residual spraying
entomological
inoculation rate
Number of infective bites received per person in a given unit of time, in
a human population
Note: This rate is the product of the “human biting rate” (the number
of bites per person per day by vector mosquitoes) and the sporozoite
rate (proportion of vector mosquitoes that are infective). At low levels of
transmission, the estimated entomological inoculation rate may not be
reliable, and alternative methods should be considered for evaluating
transmission risk.
14
epidemic Occurrence of a number of malaria cases highly in excess of that
expected in a given place and time
Note: Seasonal increases in the incidence of malaria should not be
confused with epidemics.
epidemiological
investigation
Study of the environmental, human and entomological factors that
determine the incidence or prevalence of infection or disease
Note: In malaria elimination, epidemiological investigation is a part of
surveillance operations and involves ascertaining the origin and means of
transmission of any malaria case discovered. It involves epidemiological
surveys, localized mass blood examinations and entomological surveys
to ascertain the existence and nature of any malaria foci in surrounding
areas, to establish whether transmission is taking place and, if it is, its
source and potential to spread.
erythrocytic cycle Portion of the life cycle of the malaria parasite from merozoite
invasion of red blood cells to schizont rupture. The duration is
approximately 24 h in P. knowlesi, 48 h in P. falciparum, P. ovale and
P. vivax and 72 h in P. malariae.
exophagy Tendency of mosquitoes to feed outdoors
Note: Contrasts with endophagy; usually quantified as the proportions
biting hosts outdoors versus indoors, conveniently assessed by
comparative human landing catches outdoors and indoors or by
observation of biting rates on non-human hosts outdoors
exophily Tendency of mosquitoes to rest outdoors
Note: Contrasts with endophily; usually quantified as proportions resting
outdoors and indoors; used in estimating outdoor transmission risks
experimental
huts
For vector investigations, simulated house with entry and exit traps
for sampling mosquitoes entering and exiting, blood-feeding indoors
(when a host is present) and surviving or dying in each sub-sample,
per day or night
Note: Experimental huts are used in standard protocols to evaluate indoor
treatments (indoor residual spraying and insecticide-treated nets) against
endophilic mosquitoes.
fixed-dose
combination
A combination in which two antimalarial medicines are formulated
together in the same tablet, capsule, powder, suspension or granule
focus, malaria A defined circumscribed area situated in a currently or formerly
malarious area that contains the epidemiological and ecological
factors necessary for malaria transmission
Note: Foci can be classified as active, residual non-active or cleared.
gametocyte Sexual stage of malaria parasites that can potentially infect
anopheline mosquitoes when ingested during a blood meal
gametocyte rate Percentage of individuals in a defined population in whom sexual
forms of malaria parasites have been detected
Note: This term is generally used to refer to
P. falciparum. The detection method used should be mentioned when
citing a gametocyte rate. The percentage of cases of falciparum malaria
with gametocytes is an indicator of the timeliness of diagnosis and
treatment of malaria.
WHO MALARIA TERMINOLOGY
15
geographical
reconnaissance
Censuses and mapping to determine the distribution of the human
population and other features relevant for malaria transmission in
order to guide interventions
Note: Geographical reconnaissance provides the basis for selecting field
centres and depots, for designing schedules and itineraries of operations,
planning deployment of transport and assessing completion of planned
activities. It can also be used to define, as accurately as possible, the
geographical limits of malaria-endemic areas and to assess epidemic
potential.
gonotrophic
cycle
Each complete round of ovarian development in the female mosquito,
usually after ingestion of a blood meal, to yield a batch of eggs.
Gonotrophic harmony is achieved when every blood meal results in
one batch of eggs from the gonotrophic cycle.
Note: Temperature and other environmental factors aect the duration
of the gonotrophic cycle, which takes a few days or weeks, strongly
influencing vectorial capacity. Before completion of the first gonotrophic
cycle, the adult female mosquito is nulliparous; after laying eggs, she is
parous; after successive gonotrophic cycles, she is primiparous, 2-parous,
3-parous, 4-parous, et seq.
gonotrophic
discordance
(dissociation)
Female mosquitoes that take more than one blood meal per
gonotrophic cycle
hibernation Process in which mosquitoes at one or several stages (eggs, larvae,
pupae, adults) survive by means of behavioural or physiological
changes during cold periods
house Any structure other than a tent or mobile shelter in which humans sleep
household The ecosystem, including people and animals occupying the same
house and the accompanying vectors
house-spraying Application of liquid insecticide formulation to specified (mostly
interior) surfaces of buildings
human landing catch
A method for collecting vectors as they land on individuals
Note: The purpose is to monitor exposure of the human population to
vector populations. It is used for estimating the “human biting rate”, a basic
factor for calculating the basic reproduction number and the vectorial
capacity in epidemiological studies.
hyperparasit aemia A high density of parasites in the blood, which increases the risk that a
patient’s condition will deteriorate and become severe malaria
Note: See the current WHO definition (Guidelines for the treatment of
malaria. Third edition)
hypnozoite Persistent liver stage of P. vivax and P. ovale malaria that remains
dormant in host hepatocytes for variable periods, from 3 weeks to 1
year (exceptionally even longer), before activation and development
into a pre-erythrocytic schizont, which then causes a blood-stage
infection (relapse)
importation rate Rate of influx of parasites via infected individuals or infected Anopheles
spp. mosquitoes
Note “Infected individuals” includes residents infected while visiting
endemic areas as well as infected immigrants. This term replaces the term
vulnerability.
16
importation risk Probability of influx of infected individuals and/or infective anopheline
mosquitoes
Note: Also referred to as “vulnerability”
incidence, malaria Number of newly diagnosed malaria cases during a defined period in
a specified population
incubation period Period between inoculation of malaria parasites and onset of clinical
symptoms
Note: The shortest incubation period in mosquito-borne infections ranges
from 7 days for
P. falciparum to 23 days for P. malariae malaria. The
long incubation for P. vivax and P. ovale malaria (from 3 weeks to 1 year
and exceptionally many years) is due to activation of hypnozoites. The
incubation period may be shorter in blood-induced infections than in
sporozoite-induced infections, depending on the size of the inoculum.
index, host preference Proportion of blood-fed female Anopheles mosquitoes that fed on the
host species and/or individual of interest
Note: Blood-fed female Anopheles mosquitoes are sampled at
representative resting sites, and the blood meal of each host species
or individual is identified. The methods include “precipitin testing” and
molecular assays.
index, human blood Proportion of mosquito blood meals from humans
index, parasite-density Mean parasite density on slides examined and found positive for
a sample of the population; calculated as the geometric mean of
individual parasite density counts
indoor residual
spraying
Operational procedure and strategy for malaria vector control
involving spraying interior surfaces of dwellings with a residual
insecticide to kill or repel endophilic mosquitoes
indoors Inside any shelter likely to be used by humans or animals, where
mosquitoes may feed or rest
Note: Where indoor-resting mosquitoes can be targeted for indoor
residual spraying
infection, chronic Long-term presence of parasitaemia that is not causing acute or
obvious illness but could potentially be transmitted
infection, mixed Malaria infection with more than one species of Plasmodium
infection, reservoir of Any person or animal in which plasmodia live and multiply, such that
they can be transmitted to a susceptible host
infection,
submicroscopic
Low-density blood-stage malaria infections that are not detected by
conventional microscopy
infectious Capable of transmitting infection, a term commonly applied to human
hosts
infective Capable of producing infection, a term commonly applied to parasites
(e.g. gametocytes, sporozoites) or to the vector (mosquito)
infectivity
Ability of a given Plasmodium strain to establish infection in susceptible
humans and develop in competent Anopheles mosquitoes
WHO MALARIA TERMINOLOGY
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insecticide Chemical product (natural or synthetic) that kills insects. Ovicides
kill eggs; larvicides (larvacides) kill larvae; pupacides kill pupae;
adulticides kill adult mosquitoes. Residual insecticides remain active
for an extended period
Note: Insecticides used for malaria vector control are approved by the
WHO Pesticide Evaluation Scheme (WHOPES, http://www.who.int/
whopes/).
insecticide, cross-
resistance
Resistance to one insecticide by a mechanism that also confers
resistance to another insecticide, even when the insect population has
not been selected by exposure to the latter
insecticide
discriminating dose,
or diagnostic dose for
resistance
Amount of an insecticide (usually expressed as the concentration
per standard period of exposure), which, in a sample of mosquitoes
containing resistant individuals, distinguishes between susceptible and
resistant phenotypes and determines their respective proportions
Note: When the genetic factor for resistance is either dominant or
recessive, only one discriminating dose operates. When it is semi-
dominant, two such doses may operate: a lower discriminating dose that
kills susceptible mosquitoes only and an upper diagnostic dose that kills
both susceptible mosquitoes and heterozygous (but not homozygous)
resistant mosquitoes.
insecticide, dose Amount of active ingredient of insecticide applied per unit area of
treatment (mg/m
2
) for indoor residual spraying and treated mosquito
nets, or per unit of space (mg/m
3
) for space spraying and per unit
area of application (g/ha or mg/m
2
) or per volume of water (mg/L) for
larvicides
insecticide, mixture Insecticide product consisting of two or more active ingredients mixed
as one formulation so that, when applied, the mosquito will contact
both simultaneously
insecticide mosaic Strategy for mitigating resistance, whereby insecticides with dierent
modes of action are applied in dierent parts of an area under
coverage (usually in a grid pattern), so that parts of the mosquito
populations are exposed to one insecticide and others to another
Note: This is ideally combined with insecticide rotation, whereby the
treatments of the mosaic are switched between areas periodically.
insecticide resistance Property of mosquitoes to survive exposure to a standard dose
of insecticide; may be the result of physiological or behavioural
adaptation
Note: The emergence of insecticide resistance in a vector population
is an evolutionary phenomenon due to either behavioural avoidance
(e.g. exophily instead of endophily) or physiological factors whereby the
insecticide is metabolized, not potentiated, or absorbed less than by
susceptible mosquitoes.
insecticide rotation Strategy involving sequential applications of insecticides with dierent
modes of action to delay or mitigate resistance
insecticide tolerance Less-than-average susceptibility to insecticide but not inherited as
resistance
insecticide, contact Insecticide that exerts a toxic action on mosquitoes when they rest on a
treated surface; the insecticide is absorbed via the tarsi (feet).
insecticide, fumigant Insecticide that acts by releasing vapour from a volatile substance
18
insecticide, residual Insecticide that, when suitably applied onto a surface, maintains
its insecticidal activity for a considerable time by either contact or
fumigant action
integrated vector
management
Rational decision-making for optimal use of resources for vector
control
Note: The aim is to improve the ecacy, cost-eectiveness, ecological
soundness and sustainability of vector control activities against vector-
borne diseases.
intermittent preventive
treatment in infants
A full therapeutic course of sulfadoxine-pyrimethamine delivered to
infants in co-administration with DTP2/Penta2, DTP3/Penta3 and
measles immunization, regardless of whether the infant is infected with
malaria
intermittent preventive
treatment in
pregnancy
A full therapeutic course of antimalarial medicine given to pregnant
women at routine prenatal visits, regardless of whether the woman is
infected with malaria
invasive species
A non-native species that establishes in a new ecosystem, and causes,
or has the potential to cause, harm to the environment, economy, or
human health.
Note: In malaria, it refers to Anopheles species.
larval source
management
Management of aquatic habitats (water bodies) that are potential
habitats for mosquito larvae, in order to prevent completion of
development of the immature stages
Note: The four types of larval source management are: habitat
modification, which is a permanent alteration of the environment, e.g.
land reclamation; habitat manipulation, which is a recurrent activity, e.g.
flushing of streams; larviciding, which is regular application of biological
or chemical insecticides to water bodies; and biological control, which
consists of the introduction of natural predators into water bodies.
larvicide Substance used to kill mosquito larvae
Note: Larvicides are applied in the form of oils (to asphyxiate larvae and
pupae), emulsions or small pellets or granules of inert carrier impregnated
with insecticide, which is released gradually when they are placed in
water.
latent period For P. vivax and P. ovale infections, the period between the primary
infection and subsequent relapses. This stage is asymptomatic;
parasites are absent from the bloodstream but present in hepatocytes.
long-lasting
insecticidal net
A factory-treated mosquito net made of material into which insecticide
is incorporated or bound around the fibres. The net must retain its
eective biological activity for at least 20 WHO standard washes
under laboratory conditions and 3 years of recommended use under
field conditions.
malaria case (See Case, malaria)
malaria, cerebral (See Cerebral malaria)
malaria control Reduction of disease incidence, prevalence, morbidity or mortality to
a locally acceptable level as a result of deliberate eorts. Continued
interventions are required to sustain control.
WHO MALARIA TERMINOLOGY
19
malaria elimination Interruption of local transmission (reduction to zero incidence of
indigenous cases) of a specified malaria parasite in a defined
geographical area as a result of deliberate activities. Continued
measures to prevent re-establishment of transmission are required.
Note: The certification of malaria elimination in a country will require that
local transmission is interrupted for all human malaria parasites.
malaria eradication Permanent reduction to zero of the worldwide incidence of infection
caused by human malaria parasites as a result of deliberate activities.
Interventions are no longer required once eradication has been
achieved.
malaria infection Presence of Plasmodium
parasites in blood or tissues, confirmed by
diagnostic testing
Note: Diagnostic testing could consist of microscopy, rapid diagnostic
testing or nucleic acid-based amplification (e.g. polymerase chain
reaction assays to detect parasite DNA or RNA).
malaria mortality rate Number of deaths from malaria per unit of population during a
defined period
malaria pigment
(haemozoin)
A brown-to-black granular material formed by malaria parasites
as a by-product of haemoglobin digestion. Pigment is evident in
mature trophozoites and schizonts. It may also be phagocytosed by
monocytes, macrophages and polymorphonuclear neutrophils.
malaria prevalence
(parasite prevalence)
Proportion of a specified population with malaria infection at one time
malaria receptivity
Degree to which an ecosystem in a given area at a given time allows
for the transmission of Plasmodium spp. from a human through a
vector mosquito to another human.
Note: This concept reflects vectorial capacity, susceptibility of the
human population to malaria infection, and the strength of the health
system, including malaria interventions. Receptivity depends on vector
susceptibility to particular species of Plasmodium, and is influenced by
ecological and climatic factors.
malaria reintroduction Malaria reintroduction is the occurrence of introduced cases (cases
of the first-generation local transmission that are epidemiologically
linked to a confirmed imported case) in a country or area where the
disease had previously been eliminated
Note: Malaria reintroduction is dierent from re-establishment of malaria
transmission (see definition).
malaria risk
stratification
Classification of geographical areas or localities according to factors
that determine receptivity and vulnerability to malaria transmission
malaria stratification Classification of geographical areas or localities according to
epidemiological, ecological, social and economic determinants for the
purpose of guiding malaria interventions
malaria, cross-border Malaria transmission associated with the movement of individuals or
mosquitoes across borders
malaria-free Describes an area in which there is no continuing local mosquito-
borne malaria transmission and the risk for acquiring malaria is
limited to infection from introduced cases
20
malariogenic potential
Potential level of transmission in a given area arising from the
combination of malaria receptivity, importation rate of malaria
parasites and infectivity.
Note: The concept of malariogenic potential is most relevant for
elimination and prevention of re-establishment when indigenous
transmission is mostly or entirely eliminated.
malariometric survey Survey conducted in a representative sample of selected age groups
to estimate the prevalence of malaria and coverage of interventions
Note: Current standards for such surveys are malaria indicator surveys
and related demographic and health surveys or multiple indicator cluster
surveys.
malarious area Area in which transmission of malaria is occurring or has occurred
during the preceding 3 years
mass drug
administration
Administration of antimalarial treatment to all age groups of a
defined population or every person living in a defined geographical
area (except those for whom the medicine is contraindicated) at
approximately the same time and often at repeated intervals
mass screening Population-wide assessment of risk factors for malaria infection to
identify subgroups for further intervention, such as diagnostic testing,
treatment or preventive services
mass screening,
testing and treatment
Screening of an entire population for risk factors, testing individuals at
risk and treating those with a positive test result
mass testing and focal
drug administration
Testing a population and treating groups of individuals or entire
households in which one or more infections is detected
mass testing and
treatment
Testing an entire population and treating individuals with a positive
test result
medicine safety Characteristics of a medicine that reflects its potential to cause harm,
including the important identified risks of a drug and important
potential risks
Note: The medicine safety specification should also address the
populations potentially at-risk (where the product is likely to be used), and
outstanding safety questions which require further investigation to refine
the benefit-risk profile during the post-approval period (Adapted from
ICH E2E definition).
merozoite Extracellular stage of a parasite released into host plasma when a
hepatic or erythrocytic schizont ruptures; the merozoites can then
invade red blood cells.
monotherapy Antimalarial treatment with a single active compound or a synergistic
combination of two compounds with related mechanisms of action
national focus register Centralized database of all foci of malaria infection in a country, which
includes relevant data on physical geography, parasites, hosts and
vectors for each focus
national malaria case
register
Centralized database with individual records of all malaria cases
registered in a country
WHO MALARIA TERMINOLOGY
21
net, insecticide-
treated
Mosquito net that repels, disables or kills mosquitoes that come into
contact with the insecticide on the netting material. The two categories
of insecticide-treated net are:
• conventionally treated net: a mosquito net that has been treated
by dipping it into a WHO-recommended insecticide. To ensure
its continued insecticidal eect, the net should be re-treated
periodically.
• long-lasting insecticidal net: a factory-treated mosquito net
made of netting material with insecticide incorporated within
or bound around the fibres. The net must retain its eective
biological activity for at least 20 WHO standard washes under
laboratory conditions and 3 years of recommended use under
field conditions.
Note: Untreated mosquito nets can also provide substantial protection
against mosquito bites, but they have less eect against vectorial capacity
and transmission rates. See also Long-lasting insecticidal net.
oocyst The stage of malaria parasite that develops from the ookinete; the
oocyst grows on the outer wall of the midgut of the female mosquito.
oocyst rate Percentage of female Anopheles mosquitoes with oocysts on the
midgut
ookinete Motile stage of malaria parasite after fertilization of macrogamete
and preceding oocyst formation
parasitaemia Presence of parasites in the blood
Note: If this condition is not accompanied by symptoms of malaria, it is
known as asymptomatic parasitaemia
parasitaemia,
asymptomatic
The presence of asexual parasites in the blood without symptoms of
illness
parasite clearance
time
Time between first drug administration and the first examination in
which no parasites are present in the blood by microscopy
Note: The time depends on the sensitivity of the method used to detect the
parasite.
parasite density Number of asexual parasites per unit volume of blood or per number
of red blood cells
Note: Any parasite density can lead to clinical illness; however, the
likelihood of clinical illness generally increases with increasing parasite
density.
parasite density, low Presence of Plasmodium parasites in the blood at parasite density
below 100 parasites/μl
Note: The term should be accompanied by a description of the method
of quantification. The terms “asymptomatic, submicroscopic and low
density” are dierent and should not be used inter-changeably.
patent period Period during which malaria parasitaemia is detectable
Plasmodium Genus of protozoan blood parasites of vertebrates that includes the
causal agents of malaria.
P. falciparum, P. malariae, P. ovale and
P. vivax cause malaria in humans. Human infection with the monkey
malaria parasite P. knowlesi and very occasionally with other simian
malaria species may occur in tropical forest areas.
22
population at risk Population living in a geographical area where locally acquired
malaria cases have occurred in the past 3 years
population, target An implementation unit targeted for activities or services (e.g.
prevention, treatment)
pre-erythrocytic
development
Development of the malaria parasite from the time it first enters the
host and invades liver cells until the hepatic schizont ruptures
Note: After sporozoites are inoculated into a human by a female
anopheline mosquito, they invade hepatocytes in the host liver and
multiply there for a period ranging from 5.5 (
P. falciparum) to 25 days
(P. malariae), forming exoerythrocytic schizonts. These then rupture,
liberating merozoites into the bloodstream, where they subsequently
invade red blood cells. In vivax and ovale infections, some sporozoites
remain dormant in the liver in the form of hypnozoites for periods of 3
weeks to 12 months and exceptionally several years.
pre-patent period Period between inoculation of parasites and the first appearance of
parasitaemia
prequalification Process to ensure that health products are safe, appropriate and meet
stringent quality standards for international procurement
Note: Health products are prequalified by an assessment of product
dossiers, inspection of manufacturing and testing sites, quality control
testing in the case of vaccines and medicines, validation of the
performance of diagnostic tests and verification that the products are
suitable for use in the destination countries.
preventive
chemotherapy
Use of medicines either alone or in combination to prevent malaria
infections and their consequences
Note: Preventive chemotherapy includes chemoprophylaxis, intermittent
preventive treatment of infants and pregnant women, seasonal malaria
chemoprevention and mass drug administration.
prophylaxis Any method of protection from or prevention of disease; when applied
to chemotherapy, it is commonly termed “chemoprophylaxis”.
prophylaxis, causal Complete prevention of erythrocytic infection by destroying the pre-
erythrocytic forms of the parasite
rapid diagnostic test Immunochromatographic lateral flow device for rapid detection of
malaria parasite antigens
rapid diagnostic test,
combination
Malaria rapid diagnostic test that can detect a number of dierent
malaria species
rapid diagnostic test
positivity rate
Proportion of positive results among all rapid diagnostic tests
performed
reactive focal
screening, testing,
treating or drug
administration
Screening, testing, treating or administering drugs to a subset of a
population in a given area in response to the detection of an infected
person
receptivity Receptivity of an ecosystem to transmission of malaria
Note: A receptive ecosystem should have e.g. the presence of competent
vectors, a suitable climate and a susceptible population.
WHO MALARIA TERMINOLOGY
23
recrudescence Recurrence of asexual parasitaemia of the same genotype(s) that
caused the original illness, due to incomplete clearance of asexual
parasites after antimalarial treatment.
Note: Recrudescence is dierent from reinfection with a parasite of
the same or dierent genotype(s) and relapse in P. vivax and P. ovale
infections.
recurrence Reappearance of asexual parasitaemia after treatment, due to
recrudescence, relapse (in
P. vivax and P. ovale infections only) or a
new infection
reinfection A new infection that follows a primary infection; can be distinguished
from recrudescence by the parasite genotype, which is often (but not
always) dierent from that which caused the initial infection
reintroduction risk The risk that endemic malaria will be re-established in a specific area,
after its elimination
Note: The risk is typically determined by factors including climate, altitude,
vector populations, human susceptibility, socio-economic status, urban or
rural and coverage of interventions.
relapse Recurrence of asexual parasitaemia in P. vivax or P. ovale infections
arising from hypnozoites
Note: Relapse occurs when the blood-stage infection has been eliminated
but hypnozoites persist in the liver and mature to form hepatic schizonts.
After an interval, generally from 3 weeks to 1 year, the hepatic schizonts
rupture and liberate merozoites into the bloodstream.
repellent Any substance that causes avoidance in mosquitoes, especially
substances that deter them from settling on the skin of the host
(topical repellent) or entering an area or room (area repellent, spatial
repellent, excito-repellent)
resistance (See Drug resistance, Insecticide resistance)
ring form (ring stage,
ring-stage trophozoite)
Young, usually ring-shaped malaria trophozoites, before pigment is
evident by microscopy
schizont Stage of the malaria parasite in host liver cells (hepatic schizont)
or red blood cells (erythrocytic schizont) that is undergoing nuclear
division by schizogony and, consequently, has more than one nucleus
screening Identification of groups at risk that may require further intervention,
such as diagnostic testing, treatment or preventive services
selection pressure The force of an external agent that confers preferential survival;
examples are the pressure of antimalarial medicines on malaria
parasites and of insecticides on anopheline mosquitoes
Note: The term is applicable to human populations as well. As a result of
selection pressure by malaria, certain genetic disorders (e.g. sickle-cell
anaemia and glucose 6-phosphate dehydrogenase deficiency) that reduce
the risk of severe malaria are more frequent in malaria-endemic areas.
sensitivity (of a test) Measured as the proportion of people with malaria infection (true
positives) who have a positive result
serological assay Procedure used to measure antimalarial antibodies in serum
severe anaemia
Haemoglobin concentration of < 5 g/100 mL (haematocrit < 15%)
24
severe falciparum
malaria
Acute falciparum malaria with signs of severe illness and/or evidence
of vital organ dysfunction
Note: See current WHO definition (Guidelines for the treatment of malaria.
Third edition)
single-dose regimen Administration of a medicine as a single dose to achieve a therapeutic
objective
slide positivity rate Proportion of blood smears found to be positive for Plasmodium
among all blood smears examined
specificity (of a test) Measured as the proportion of people without malaria infection (true
negatives) who have a negative result
sporozoite Motile stage of the malaria parasite that is inoculated by a feeding
female anopheline mosquito and may cause infection
sporozoite rate Percentage of female Anopheles mosquitoes with sporozoites in the
salivary glands
spray round Spraying of all sprayable structures in an area designated for
coverage in an indoor residual spraying programme during a discrete
period
Note: Depending on the residual activity of the insecticide and also on
the dynamics of transmission, one or more spray rounds a year may be
required in the same area.
sprayable In the context of a malaria vector control programme, a unit (dwelling,
house, room, shelter, structure, surface) suitable for spraying or
required to be sprayed
Note: In house-spraying operations, usually implemented by indoor
residual spraying
spraying cycle Repetition of spraying operations at regular intervals, often designated
in terms of the interval between repetitions, e.g. a 6-month spraying
cycle when spraying is repeated after a 6-month interval
Note: Not to be confused with “spray round”
spraying frequency Number of regular applications of insecticide per house per year,
usually by indoor residual spraying
spraying interval Time between successive applications of insecticide
spraying, focal Spray coverage by indoor residual spraying and/or space spraying of
houses or habitats in a limited geographical area
spraying, residual Spraying the interior walls and ceilings of dwellings with a residual
insecticide to kill or repel endophilic mosquito vectors of malaria
surveillance Continuous, systematic collection, analysis and interpretation of
disease-specific data and use in planning, implementing and
evaluating public health practice
Note: Surveillance can be done at dierent levels of the health care system
(e.g. health facilities, the community), with dierent detection systems (e.g.
case-based: active or passive) and sampling strategies (e.g. sentinel sites,
surveys).
WHO MALARIA TERMINOLOGY
25
testing, malaria Use of a malaria diagnostic test to determine whether an individual
has malaria infection
tolerance A response in a human or mosquito host to a given quantum of
infection, toxicant or drug that is less than expected
transmission intensity The frequency with which people living in an area are bitten by
anopheline mosquitoes carrying human malaria sporozoites
Note: Transmission intensity is often expressed as the annual entomological
inoculation rate, which is the average number of inoculations with
malaria parasites estimated to be received by one person in a given
period. Because of the diculty of measuring entomological inoculation
rate, parasite prevalence in young children is often used as a proxy for
transmission intensity.
transmission season Period of the year during which most mosquito-borne transmission of
malaria infection occurs
transmission,
re-establishment of
Renewed presence of a measurable incidence of locally acquired
malaria infection due to repeated cycles of mosquito-borne infections
in an area in which transmission had been interrupted
Note: A minimum indication of possible re-establishment of transmission
would be the occurrence of three or more indigenous malaria cases of the
same species per year in the same focus, for 3 consecutive years.
transmission,
interruption of
Cessation of mosquito-borne transmission of malaria in a
geographical area as a result of the application of antimalarial
measures
transmission,
perennial
Transmission that occurs throughout the year with no great variation in
intensity
transmission, residual Persistence of malaria transmission following the implementation in
time and space of a widely eective malaria programme
Note: The sources of and risks for “residual transmission” may vary by
location, time and the existing components of the current “eective
malaria programme”.
transmission, seasonal Transmission that occurs only during some months of the year and is
markedly reduced during other months
transmission, stable Epidemiological type of malaria transmission characterized by a
steady prevalence pattern, with little variation from one year to an-
other except as the result of rapid scaling up of malaria interventions
or exceptional environmental changes that aect transmission
Note: In areas with stable transmission, the aected population often has
high levels of immunity, and malaria vectors usually have high longevity
and human-biting rates.
transmission, unstable Epidemiological type of malaria transmission characterized by large
variation in incidence patterns from one year to another
Note: In areas with unstable transmission, epidemics are common and the
population usually has little immunity.
26
trap, mosquito Device designed for capturing mosquitoes with or without attractant
components (light, CO
2
, living baits, suction)
Note: Mosquito traps are used to sample the density of mosquitoes or
to study the eects of attractants, repellents or control interventions;
mosquito trapping may also be intended for their control. This includes:
i) individual devices used to attract mosquitoes with appropriate lures
(light, CO
2
, living baits, etc.); ii) window traps placed on points of entry or
exit of mosquitoes into houses, without any lure and being as unobtrusive
as possible, meant to study factors such as indoor feeding, delayed
mortality or repellency eect of the insecticide used for IRS; iii) killing traps
to attract mosquitoes by powerful attractants, chemical or physical, to their
death.
treatment failure Inability to clear malarial parasitaemia or prevent recrudescence after
administration of an antimalarial medicine, regardless of whether
clinical symptoms are resolved
treatment,
anti-relapse
Antimalarial treatment designed to kill hypnozoites and thereby
prevent relapses or late primary infections with P. vivax or P. ovale
treatment, directly
observed
Treatment administered under the direct observation of a health care
worker
treatment, first-line Treatment recommended in national treatment guidelines as the
medicine of choice for treating malaria
treatment, second-line Treatment used after failure of first-line treatment or in patients who
are allergic to or unable to tolerate the first-line treatment
treatment,
presumptive
Administration of an antimalarial drug or drugs to people with
suspected malaria without testing or before the results of blood
examinations are available
Note: This practice may lead to wrong treatment of the underlying disease
and is only acceptable in exceptional circumstances. It should be reported
to guide appropriate action and improvement of the situation.
treatment, preventive Intermittent administration of a full therapeutic course of an
antimalarial either alone or in combination to prevent malarial illness
by maintaining therapeutic drug levels in the blood throughout the
period of greatest risk.
Note: WHO recommended preventive treatment includes intermittent
preventive treatment of infants and pregnant women and seasonal
malaria chemoprevention.
treatment, radical Treatment to achieve complete cure. This applies only to vivax and
ovale infections and consists of the use of medicines that destroy both
blood and liver stages of the parasite.
trophozoite The stage of development of malaria parasites growing within host
red blood cells from the ring stage to just before nuclear division.
Trophozoites contain malaria pigment that is visible by microscopy.
uncomplicated malaria Symptomatic malaria parasitaemia without signs of severity or
evidence of vital organ dysfunction
Note: See current WHO definition (Guidelines for the treatment of
malaria. Third edition). Malaria-associated disease can be defined more
specifically by criteria for the degree of fever (e.g. temperature > 37.5 °C)
and level of parasitaemia (e.g. > 5000 parasites/µL).
WHO MALARIA TERMINOLOGY
27
vector In malaria, adult females of any mosquito species in which
Plasmodium undergoes its sexual cycle (whereby the mosquito is
the definitive host of the parasite) to the infective sporozoite stage
(completion of extrinsic development), ready for transmission when a
vertebrate host is bitten
Note: Malaria vector species are usually implicated (incriminated) after
field collection and dissection indicates that the salivary glands are
infected with sporozoites; specific assays can be used to detect and
identify circumsporozoite protein, especially where infection rates are low.
vector competence For malaria, the ability of the mosquito to support completion of
malaria parasite development after zygote formation and oocyst
formation, development and release of sporozoites that migrate to
salivary glands, allowing transmission of viable sporozoites when the
infective female mosquito feeds again
Note: Human malarias are transmitted exclusively by competent species of
Anopheles mosquitoes; various plasmodia are transmitted by competent
species of mosquitoes of the genera Aedes, Anopheles and Culex and
other haematophagous Diptera.
vector control Measures of any kind against malaria-transmitting mosquitoes,
intended to limit their ability to transmit the disease
Note: Ideally, malaria vector control results in reduction of malaria
transmission rates, by reducing the vectorial capacity, to a point at which
transmission is interrupted.
vector susceptibility The degree to which a mosquito population is susceptible (i.e. not
resistant) to insecticides
Note: Not to be confused with “vector competence”
vector, principal The species of Anopheles mainly responsible for transmitting malaria
in any particular circumstance
Note: Principal vectors may overlap seasonally or alternate in importance.
vector, secondary or
subsidiary
Species of Anopheles thought to play a lesser role in transmission than
the principal vector; capable of maintaining malaria transmission at a
reduced level
vectorial capacity Number of new infections that the population of a given vector would
induce per case per day at a given place and time, assuming that the
human population is and remains fully susceptible to malaria
vigilance A function of the public health services for preventing reintroduction of
malaria. Vigilance consists of close monitoring for any occurrence of
malaria in receptive areas and application of the necessary measures
to prevent re-establishment of transmission.
28
Age standardization of rates: a new WHO standard. Geneva: World Health
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Core structure for training curricula on integrated vector management. Geneva: World
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th
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Indoor residual spraying: an operational manual for indoor residual spraying for
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global review of evidence and practice. Geneva: World Health Organization; 2013.
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reconnaissance of target populations in malaria elimination zones. Malar J 2010;9:289.
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treatment to eliminate vivax malaria: lessons from the past. Malar J 2014;13:51.
Larval source management – operational manual. Geneva: World Health
Organization; 2013.
Lilienfeld AM, Lilienfeld DE. Foundations of epidemiology. 2
nd
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University Press; 1980.
Lymphatic filariasis: a manual for national elimination programmes. Geneva: World
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nd
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rd
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rd
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30
biting-capture, biting
collection, human bait
collection
Sampling of populations of mosquitoes and other haematophagous
insects by capture when they bite on human bait or other hosts
Note: Discouraged for ethical reasons, to prevent human exposure to
risks of transmission of vector-borne diseases; human landing collection
is the recommended alternative.
breeding site, breeding
place
Obsolete term for larval habitat: site at which developmental stages
of mosquitoes (eggs, larvae, pupae) are found, including sites that
appear to be ecologically suitable for particular species
cure, clinical Relief of symptoms of a malaria attack (e.g. by chemotherapeutic
action against asexual erythrocytic parasites), without complete
elimination of the infection
cure, suppressive Complete elimination of the parasite from the body by means of
continuous suppressive treatment
discharge register List of patients who leave inpatient hospital care. Discharge registers
should contain the date of admission, patient’s name, residence, age,
sex, diagnosis, length of stay and reason for leaving (discharged,
died, transferred, absconded). This information should be abstracted
from the patient file by appropriately trained sta.
drug failure Absence or insuciency of drug action after administration of a
normally eective dose. It is important to discriminate between
such causes of drug failure as deficient absorption, unusual rate of
degradation or excretion of the drug and resistance of the parasite.
infection interval Period elapsing from the time an individual is infected until he or
she becomes infectious to others. In malaria, the infection interval
is the period between the inoculation of a human being with
sporozoites and the appearance of gametocytes potentially infective
to mosquitos. To be distinguished from incubation interval and
incubation period.
malaria baseline The malaria burden that would be present in a specific area if there
were no control activities. Also termed “intrinsic malaria transmission
level”
malaria, refractory Term used by some authors to describe persistence or slow, gradual
reduction in the prevalence of malaria despite total-coverage
spraying
malaria, responsive Term used by some authors to describe malaria that is rapidly
reduced in prevalence by total-coverage spraying soon after the
beginning of the attack phase
malaria, sporadic Term applied to malaria when autochthonous cases are too few and
scattered to have any appreciable eect on the community. Such
cases are often due to relapses of a previous infection. For purposes
of epidemiological classification by origin of infection, the term
“relapsing “ is preferred.
Archived terms
WHO MALARIA TERMINOLOGY
31
mass blood
examination
Examination of the blood of all members of a unit of population,
which may be repeated at certain intervals. Blood specimens are
commonly obtained during house-to-house visits. Unlike other
case-detection methods, mass blood examinations are used to
detect all people harbouring malaria parasites, even those who
have no clinical symptoms; they thus supplement routine methods
in problem areas and are useful for demonstrating the proportion
of asymptomatic carriers present in the community examined. Mass
blood examination forms part of case-detection activities and must
be distinguished from malariometric surveys, which are carried out
on a sampling basis in selected groups.
mass primaquine
preventive treatment
Administration of primaquine anti-relapse therapy to each individual
in a defined population or geographical area during the low-trans-
mission season to eliminate long-latency hypnozoites in infected
people, with the aim of reducing P. vivax malaria transmission during
the next transmission season.
Note: For safety reasons, recipients should be tested for glucose
6-phosphate dehydrogenase activity before the intervention.
outbreak A case or a greater number of cases of locally transmitted infection
than would be expected at a particular time and place
Note: The correct term is “epidemic”.
outpatient register List of patients seen in consultation at a health facility. A register may
include the date of consultation, patient’s age, place of residence and
presenting health complaint, tests performed and diagnosis
phase, attack In malaria eradication terminology, the phase during which
antimalarial measures that can be used on a large scale for
interrupting transmission are applied for total coverage of an
operational area. This phase is sometimes called the period of total
coverage spraying.
phase, consolidation In malaria eradication terminology, the phase that follows the attack
phase. It is characterized by active, intense, complete surveillance,
with the objective of eliminating any remaining infections and
proving the eradication of malaria. It ends when the criteria for
eradication have been met.
phase, maintenance In malaria eradication terminology, period that begins when the
criteria for malaria eradication have been met in an operational
area and will continue until worldwide eradication has been
achieved. During this period, vigilance is exercised by the public
health services to prevent the spread of malaria imported from
across the borders of the area concerned.
phase, preparatory In malaria eradication terminology, the time devoted to preparation
for attack operations. It ends when epidemiological and
geographical reconnaissance in the operational area is completed,
central and peripheral stations and essential services are established,
sta are recruited and trained and logistics and reporting systems
are organized.
population, vulnerable Groups of people who are particularly vulnerable to malaria infection
in certain situations or contexts, such as mobile workers. Each country
should define the populations that are particularly vulnerable in the
epidemiological and social context.
population-based blood
survey
Survey in which a blood smear is taken on one or more occasions
from each individual in a given population (irrespective of history
of fever) to assess the prevalence of malaria parasitaemia (both
symptomatic and asymptomatic) in the population. Such surveys may
also provide supportive evidence of the interruption of transmission.
32
potential vector Species with vector competence and appreciable vectorial capacity
pre-eradication
programme
Preliminary operation undertaken in a country in which the general
administrative and health services are not yet able to undertake a
malaria eradication programme
pre-eradication survey Operation for the collection of accurate data on the malaria
situation, preliminary to drafting a complete plan of operations for a
malaria eradication programme. The undertaking of such a survey
presupposes the availability of evidence that transmission can be
interrupted by the methods commonly used in malaria eradication
and the existence of basic operational facilities. The period of the
pre-eradication survey ends when the plan of operations has been
prepared.
prophylaxis, absolute Absolute prevention of infection, implying destruction of inoculated
sporozoites before they can fix themselves in the tissues
prophylaxis, clinical Prevention of clinical symptoms by early destruction of erythrocytic
parasites. It is considered to suppress malaria when it permits the
continued existence of exoerythrocytic forms or of some erythrocytic
forms that will permit subsequent multiplication of the parasite after
discontinuation of the drug. All blood schizontocides are clinical
prophylactic drugs or suppressants, as they destroy merozoites
entering the bloodstream before they can establish schizogony.
This results in prevention of erythrocytic infection, or at least in its
reduction to a sub-patent level while the drug is being taken, but
overt attacks may occur after it is discontinued.
rate, malaria morbidity Number of recorded clinical cases of malaria per unit of population
over a certain period. The malaria morbidity rate is too imprecise to
be of value in malaria eradication.
rate, parasite Percentage of people in a defined age group showing, on a given
date, microscopically detectable parasites in peripheral blood. The
parasite rate should always be defined in terms of the age group
examined.
sub-perennial Transmission occurs throughout the year with peaks of markedly
greater intensity in some months.
surveillance, active A surveillance system in which public health workers seek reports on
a regular basis from participants in the surveillance system, rather
than waiting passively for the reports to be submitted
surveillance, case-
based
Each case is reported and investigated immediately and included in
the weekly reporting system.
Note: Surveillance in which all cases included in the regular reporting
system are investigated
surveillance,
community-based
Surveillance in which notification starts at community level, usually
reported by a community worker. It can be active (looking for cases)
or passive (reporting cases). Community-based surveillance may
be particularly useful during an epidemic and when syndromic case
definitions can be used.
surveillance, hospital-
based
Surveillance in which notification starts with identification by a
hospital of a patient with a particular disease or syndrome
surveillance, passive Surveillance in which reports are awaited and no attempt is made to
seek reports actively from the participants in the system.
surveillance, sentinel Collection and use of data from a random or non-random sample
of collecting sites as indicator data for the population as a whole, in
order to identify cases of a disease early or to obtain indicative data
about trends of a disease or health event that is not malaria specific
WHO MALARIA TERMINOLOGY
33
trap hut Structure adapted for trapping mosquitoes attracted by bait (human
or animal) placed inside it
Note: The purpose of trap huts is to collect a representative portion
of incoming mosquitoes and/or to test the eectiveness of an
insecticide. They are usually of simple design, often built of the
same materials as local habitations, and are provided with trapping
devices – usually one or more window traps – so that mosquitos are
trapped as they enter or leave. See also “Experimental hut”.
treatment, suppressive Treatment to prevent or eliminate clinical symptoms and/or
parasitaemia by early destruction of erythrocytic parasites. It does
not necessarily prevent or eliminate the infection, and malaria may
become overt after drug withdrawal.
treatment, targeted Administration of drugs to a group whose eligibility for treatment is
defined by age, sex or social characteristics, irrespective of infection
status (exclusion criteria may apply)
vector eciency Imprecise way of ranking vector species or populations as relatively
more or less important in transmission
Note: More dicult to calculate than vectorial capacity
vulnerability
The frequency of influx of infected individuals or groups and/or
infective anopheline mosquitoes
Note: Also referred to as “importation risk”. The term can also be applied
to the introduction of drug resistance in a specific area.
For further information please contact:
Global Malaria Programme
World Health Organization
20 Avenue Appia
CH-1211 Geneva 27
Switzerland
Email: infogmp@who.int
