ENTOMOLOGICAL GLOSSARY

This glossary is provided as a help to understanding some of the special terms which are used in relation to malaria vectors.

Annual Blood Examination Rate - ABER - 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.

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.

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.

Autogeny - ability of a female mosquito to lay eggs without the need of taking a blood meal.

Biotope - restricted area characterized by specific ecological features

Bionomics - relation between the mosquito and its environment (includes host preferences and prefered oviposition sites).

Breeding site - in mosquitoes, this generally refers to the larval breeding site (see oviposition)

Chromosome - the self-replicating genetic structures of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins. In many insects, giant chromosomes or polytene can be found in certain tissues.

Chromosomal inversion - regions where gene order has been reversed. Useful in cytotaxonomy.

Chromosomal forms - a taxonomical entity based on fixed chromosomal inversions. For example, An. gambiae is composed of 5 sympatric taxa , which are at least partially reproductively isolated, based on characteristic combinations of paracentric inversions of chromosome 2. These are called: Mopti, Bamako, Savanna, Bissau and Forest.

Cytogenetics - field of taxonomy which uses chromosomal study to distinguish individuals at specific or infra-specific level.

Diapause - another for hibernation. State of suspended animation used by female anopheline of temperate species to survive during the winter months.

Diuresis - while taking a bloodmeal, females produce a sort of clear urine. The process is a way of concentration the blood as it is ingested and allow more blood to be taken up.

Diurnal - during the daytime. The diurnal resting places of mosquitoes, especially newly-fed females, may be important in malaria control

Entomological Inoculation Rate (EIR) = 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.

Enzyme-linked immunosorbent assay. ELISA is now often used for blood meal identification and 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 An. darlingi and An. funestus. Endophilism makes the blocking of malaria transmission through application of residual insecticides to walls easier to accomplish.

Eradication - the process of removing something permanently.

Erythrocytic schizogony - the process of asexual reproduction of malaria parasites within red blood cells

Exoerythrocytic 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.

Gametocyte count - number of gametocytes per mm3 of blood. The lower the gametocyte count, the lower the infectivity of the human to the mosquito.

Glossary - a device for starting futile arguments over definitions.

Gonotrophic cycle - the process of blood-feeding, egg maturation and oviposition is repeated several times throughout the life-cycle of the female mosquito.

Halophily - marked preference for a habitat with high mineral salt content (e.g. mangrove swamps)

Haematophagy - the taking of blood. Only female mosquitoes are haematophagic.

Human blood index - the percentage of human-fed mosquitoes in a sample. To determine the blood index it is necessary to use techniques for bloodmeal identification (e.g. ELISA using host-specific anti-immunoglobulins).

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.

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.

Karyotype - a photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type; used in low-resolution physical mapping to correlate gross chromosomal abnormalities with the specific characteristics.

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.

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.

Orthologs - genes in different species that evolved from a common ancestral gene by speciation. They typically retain the same function in the course of evolution.

Oviposition - the act of finding a suitable pool of water for the female to lay her eggs. Each species will exhibit very specific preferences for oviposition sites

Parity - rate of the number of females which have laid eggs over the total number of examined females. Useful because it makes it possible to evaluate the average physiological age of a population.

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 - 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 P. vivax infection, particularly in semi-immune persons.

Pheromones are those molecules secreted by an organism that evoke a response in individuals of the same species. Not all pheromones attract potential mates. On the one hand, aggregation pheromones summon conspecific predators to a meal of palatable insects. But in the perpetual war between the eaters and the eaten, there are chemical messengers that act as double agents. (E)-¤-Farnesene may induce other aphids to flee, but, at the same time, it is believed to point the wasp Aphidius uzbekistanicus to the aphids' whereabouts. To the aphid, this semiochemical is an alarm bell; to the female Aphidius wasp, looking for a suitable host in which to deposit her eggs, it is a dinner bell.

Polymerase chain reaction (PCR) - a method for amplifying a DNA sequence using heat-stable polymerase and two 20-base primers; PCR can be used to detect the existence of the selected sequence in a DNA sample

Precipitin test - one of the biochemical tests routinely used for identifying the origin of a bloodmeal in a haematophagous insect. The test is based on the immunological recognition of the type of immunoglobulin present in the bloodmeal and can be of a precision up to the species level (alternatively, bloodmeal identification can be performed using ELISA)

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.

Randomly amplified polymorphic DNA (RAPD) - a widely used technique for amplifying anonymous stretches of DNA using PCR with random primers.

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.

Relapse - a repeated attack weeks, months, or occasionally years, after initial malaria infection. Due to re-infection of red blood cells from malaria parasites (hypnozoites) that persisted in liver cells (hepatocytes).

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. An. sergenti and An. superpictus were evading residual treatment of dwellings by resting in caves and natural fissures in earth.

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.

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.

Restriction fragment length polymorphisms (RFLPs) - a technique where the DNA strands are cut by specific endonucleases; the cut fragments are then visualized on an ethidium bromide-stained agarose gel. Sequence changes in the genome, or polymorphisms between different isolates of same same species, show up as variation in banding patterns.

Semiochemistry is the study of chemical signaling between organisms. The two types of semiochemicals described here are pheromones and kairomones.

Sibling species - morphologically similar or identical species (or 'taxa') that are reproductively isolated and can be distinguished using a variety of techniques (e.g. cytotaxonomy). Also referred to as 'cryptic' species.

Species complex - group of sibling species. The 'gambiae complex' consists of 7 species including An. gambiae s.s., An. arabiensis, An. merus, An. melas, An. bwambae and An. quadriannulatus A and B.

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.

Swarming - group of a large number of individals from the same species flying together. Swarming is very often a prelude to mating.

Sympatry - the fact of living in the same geographical area.

Trophic preferences - spectrum of hosts susceptible of providing a bloodmeal for a given species of mosquitoes.

Type-species - the species, which has features that are used to describe a taxon of a higher range (e.g. a genus or a family).

Vector competence - the ability to transmit malaria.

Vectorial capacity: In vector-borne infections such as malaria, the vectorial capacity is a concept analogous to the contact rate in directly-transmitted diseases. It is, thus, a function of (a) the vector's density in relation to its vertebrate host, (b) the frequency with which it takes blood meals on the host species, (c) the duration of the latent period in the vector, and (d) the vector's life expectancy.

Vertical transmission: Vertical transmission occurs when a parent conveys an infection to its unborn offspring, as occurs in syphilis in man or in many arboviruses of arthropods.

Zoophagy - the process of feeding on animals (example: cattle).

Zoophilous - prefers to feed on animals.

For definitions of specialized epidemiological terms, consult the Epidemiology Glossary (Section 9).