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Malaria Glossary

This glossary is provided as a help to understanding some of the special terms that are used with malaria and malaria vectors. The glossary is for the use of students and others who are interested. The definitions will be expanded as time allows. If you can't find a term here, try Google.
  • ABER - Annual Blood Examination Rate. Calculated as (number of slides examined/population) x 100. WHO recommendation for malarious areas is that the number of slides examined per month should equal at least 1% of the population.
  • Anaemia - decrease in number of red blood cells and/or quantity of hemoglobin. Malaria causes anemia through rupture of red blood cells during merozoite release. The anaemia caused may be extreme. Pallor may be visible in the patient.
  • Animal trap - A cage, generally made of cloth, that is baited with an animal such as a cow, goat, etc. Collections of mosquitoes are made on the walls of this trap to assess and compare populations biting domestic animals with populations in dwellings.
  • Anthropophagy - the process of feeding on people. Similar to anthropophilic. Anthropophilic species prefer to feed on people as opposed to animals.
  • API - Annual Parasite Incidence. API = (confirmed cases during 1 year/population under surveillance) x 1000.
  • Autochthonous - locally transmitted by mosquitoes. Differentiated from imported, congenital, or blood-borne malaria.
  • Cerebral malaria - this grave complication of malaria happens at times with P. falciparum infection and involves malaria infection of the very small capillaries that flow through the tissues of the brain. This complication has a fatality rate of 15% or more, even when treated and is extremely serious.
  • Congenital malaria - malaria acquired from the mother at birth.
  • Cryptic - an isolated case of malaria not associated with secondary cases, as determined by appropriate epidemiologicinvestigations.
  • Diurnal - during the daytime. The diurnal resting places of mosquitoes, especially newly-fed females, may be important in malaria control.
  • EIR = Entomological Inoculation Rate = mas, where ma = number of mosquito bites per night and s = proportion of those bites positive for sporozoites.
  • Elimination - The process of removing something on a temporary or semipermanent basis.
  • ELISA - enzyme-linked immunosorbent assay. ELISA is now often used to determine whether mosquito salivary glands are positive for sporozoites.
  • Endophagic - feeds indoors.
  • Endophilic - tends to inhabit/rest in indoor areas. Examples of endophilic anopheline species include Anopheles darlingi and An. funestus. Endophilism makes the blocking of malaria transmission through application of residual insecticides to walls easier to accomplish. (MacDonald 1956).
  • Eradication - The process of removing something permanently.
  • Erythrocyte - a red blood cell
  • Erythrocytic schizogony - the process of asexual reproduction of malaria parasites within red blood cells
  • Exerythrocytic schizogony - the process of asexual reproduction of malaria parasites outside of red blood cells, usually in the liver. This process is asymptomatic.
  • Exit trap - A trap constructed to capture mosquitoes that are exiting a house or structure. Exit traps are often used in studies that compare the tendency of mosquitoes to rest indoors after feeding versus to fly outside after feeding.
  • Exophagic - feeds outdoors.
  • Exophilic - tends to inhabit/rest in outdoor areas. After biting, an exophilic mosquito flies outside and rests woods, grass, or other outside areas. Exophilism makes use of residual insecticides in buildings less effective.
  • GIS - Geographic Information System
  • GPS - Global Positioning System. Common GPS systems receive data that is sensitive enough to map blocks of a city.
  • Gametocyte - the sexual reproductive stage of the malaria parasite. Gametocytes [macro- and micro-gametocytes] circulate in the blood stream, are picked up by the Anopheles mosquito, undergo sexual reproduction in the midgut of the mosquito, and attaches to the mosquito's midgut, where they form an oocyst that eventually produces sporozoites.
  • Gametocyte rate - percentage of persons in an area who carry gametocytes. Expressed as a percentage. The less the gametocyte rate of an area, the fewer infective humans are available for mosquitoes, and the less likely that transmission is to occur. (MacDonald 1956).
  • Gametocyte count - number of gametocytes per mm3 of blood. The lower the gametocyte count, the lower the infectivity of the human to the mosquito Hypnozoite - a stage of malaria parasites found in liver cells. After sporozoites invade liver cells, some develop into latent forms called hypnozoites. They become active months or years later, producing a recurrent malaria attack. Only P. vivax and P. ovale species that infect humans develop latent stage hypnozoites. Primaquine is the only available drug active against hypnozoites.
  • Hypoglycaemia - hypoglycemia -blood glucose less than the lower value of normal (70-110 mg/dl [3.9-6.1 mmol/L in SI reference units]). Glucose levels of 40 and below constitute severe hypoglycemia, a life-threatening emergency. Hypoglycemia is common in malaria, as malaria parasitized red blood cells utilize glucose 75 times faster than uninfected cells. In addition, treatment with quinine and quinidine stimulate insulin secretion, reducing blood glucose.
  • Imported malaria - A case of malaria that is brought into an area by someone who has become infected somewhere else. The person could be either a tourist or immigrant.
  • Induced malaria - Malaria acquired through artificial means (e.g. blood transfusion, dirty syringes, or malariotherapy).
  • Introduced malaria - malaria acquired by mosquito transmission from an imported case in an area where malaria is not a regular occurrence.
  • Infant parasite rate - The percentage of infants below one year old who show parasites in their blood films. If the infant parasite rate is zero for three consecutive years in a locality, this is regarded as absence of local transmission, provided that the survey is done every year and enough slides have been examined.
  • Longevity - the longevity, or length of lifespan of the mosquito is of considerable importance in malaria control. There are two reasons for this. The first is that the reproductive cycle of malaria in the mosquito takes 10-11 days, and the second is that if the mosquito lives a long time, it will be able to take several blood meals, and will have a higher chance of biting a human who has malaria parasites.
  • Macrogametocyte - the female form of the gametocyte.
  • Malaise - subjective feeling of being sick, ill, or not healthy. The feeling is generalized, varying from mild to severe in intensity. It may be the lone clinical manifestation of malaria, or may accompany other signs and symptoms, such as fever, headache, or nausea. This may be expressed as "feel achey all over," "flu-like symptoms," etc.
  • Microgametocyte - the male form of the gametocyte.
  • Oocyst - oocysts are Plasmodium cysts located in the outer stomach wall of mosquitoes, where sporozoite development takes place. When mature, the oocysts rupture and release sporozoites. Sporozoites subsequently migrate to the mosquito's salivary gland, and are injected into the host when the mosquito feeds.
  • Orthostatic hypotension - decrease in blood pressure occurring when an individual arises from a seated or lying position. A small decrease in blood pressure is normal, but large decreases are abnormal, especially if accompanied by clinical manifestations such as faintness, light-headedness, dizziness, or increased pulse. Orthostatic hypotension is a common finding in patients with malaria infections. The patient may complain of notable tiredness after conducting light office work, etc.
  • Parasitaemia - the status of having parasites. This term is often used to express the quantity of parasites in the blood. If no fever or other symptoms are present, the condition is referred to as 'asymptomatic parasitaemia.'
  • Paroxysm - paroxysm - a sudden attack or increase in intensity of a symptom, usually occurring in intervals. Malaria is classically described as producing fever paroxysms; sudden severe temperature elevations accompanied by profuse sweating. Paroxysms occurring at 48-hr intervals are typical of Plasmodium vivax infection, particularly in semi-immune persons.
  • Proportional case rate - The number of cases diagnosed as clinical malaria for every 100 patients attending hospitals and dispensaries [used in India].
  • Protozoan - A member of the Kingdom Protista. Protozoa are single-celled organisms [eukaryotes]. The single cell performs all necessary functions of metabolism and reproduction. Some protozoa are free-living, while others, including malaria parasites, depend on other organisms for their nutrients and life cycle. Malaria parasites are members of the Phylum Apicomplexa.
  • Radical Cure - treatment intended to achieve cure of P. vivax or P. malariae malaria. These two species have exoerythrocytic [outside of red blood cells i.e. in the liver] stages. Requires primaquine treatment, which destroys latent exoerythrocytic stage parasites (hypnozoites). Typical case patient: a returned traveller from Central America who has had a relapse of malaria.
  • Recrudescense - a repeated attack of malaria (short term relapse or delayed), due to the survival of malaria parasites in red blood cells. Characteristic of P. malariae infections.
  • Recurrence - a repeated attack weeks, months, or occasionally years, after initial malaria infection, also called a long-term relapse. Due to re-infection of red blood cells from malaria parasites (hypnozoites) that persisted in liver cells (hepatocytes).
  • Relapsing malaria - Renewed manifestation (of clinical symptoms and/or parasitemia) of malaria infection that is separated from previous manifestations of the same infection by an interval greater than any interval resulting from the normal periodicity of the paroxysms.
  • Refractory malaria - malaria that is not responsive to residual treatment. The cause of the lack of response to residual treatment is usually defined to be factors other than physiological insecticide resistance. Examples of causes of refractory malaria are vector exophily and zoophily with failure to enter houses. An example of refractory malaria occurred in the Jordan Valley during the early 1950s. Anopheles sergenti and Anopheles superpictus were evading residual treatment of dwellings by resting in caves and natural fissures in earth (Farid 1954).
  • Reproduction rate - Reproduction rates > 1.0 indicate an expansion of infections in a population while those < 1.0 indicate a decline in infections in the population. The goal of malaria control is to decrease the reproduction rate. This can be accomplished by altering mosquito numbers, longevity of female anophelines, biting habits, and recovery rate of gametocytemic person. Reduction of mosquito numbers through larval control is less effective by itself than causing mosquito mortality through adult control. The reason is that not only does adult control cause a reduction in mosquito numbers, but it also causes reduction in longevity of female anophelines [larval control doesn't do that]. The fewer gonotrophic cycles that a female mosquito has, the less likely that it is to transmit sporozoites (MacDonald 1956, p. 620).
  • Residual treatment - treatment of houses, animal sheds, and other buildings where people or animals spend nighttime hours with insecticide that has residual efficacy. The goal of residual treatment is to block transmission by stopping human-vector contact.
  • Splenomegaly - an enlarged spleen. A common finding in malaria patients that sometimes can be detected by physical examination. May occur in otherwise asymptomatic patients and is of use in conducting malaria surveys of a community, although it should not be the only factor considered when counting cases.
  • Sporozoite - the infective stage of the malaria parasite that is passed to the human host from the salivary glands of the mosquito. Sporozoites infect liver cells, disappearing from bloodstream within 30 minutes. The mechanism for this amazingly rapid disappearance from the bloodstream to the liver is still unknown. Sporozoites are delicate and spindle-shaped stages that are released into the haemocoel of the mosquito when the oocyst ruptures. Some eventually find their way to the salivary glands of the mosquito.
  • Sporozoite rate - The percentage of female anopheline mosquitoes of a particular species that bear sporozoites in their salivary glands. Expressed as a percentage.
  • Temperature - the optimal temperature for development of P. falciparum is 30oC [86oF], while the optimal temperature for development of P. vivax is 25oC [77oF]. The time required for development of the sexual phases of the malaria parasite in the mosquito is 10-11 days at these temperatures.
  • Tinnitus - ringing sound in the ears, a common side effect of quinine treatment.
  • Vector competence - the ability to transmit malaria. Said of Anopheles mosquitoes.
  • Zoophagy - the process of feeding on animals (example: cattle).
  • Zoophilous - prefers to feed on animals.


References

  1. Farid, M.A. 1954. Ineffectiveness of DDT residual spraying in stopping malaria transmission in the Jordan Valley. Bull. W.H.O. 11:765-783.
  2. MacDonald, G. 1956. Epidemiological basis of malaria control. Bull. W.H.O. 15:613-626.
  3. Pampana, E. 1964. A Textbook of Malaria Eradication.

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