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AnophelesAnopheles is a genus of mosquito (Culicidae). Anopheles contains several species which are vectors of malaria (e.g. Anopheles gambiae or Anopheles funestus).
Anopheles gambiaeAnopheles gambiae is the principal vector of malaria in sub-Saharan Africa.
Anopheles funestusAnopheles funestus is one of the most anthropophil vectors of malaria in Africa (Gillies and de Meillon 1968).
asymptomaticIn medicine, a disease is asymptomatic while the patient does not experience symptoms. Asymptomatic diseases may not be discovered until the patient undergoes medical tests.
bThe mosquito-to-human transmission effieciency, i.e. the proportion of sporozoite-positive mosquito bites which infect susceptible humans. The force of malaria infection is being directly proportional to the entomological inoculation rate (EIR). The factor of proportionality is defined as parameter b (Macdonald 1957). Since parameter b has not been officially termed various names are found in the literature, e.g. transmission efficiency (Gu et al. 2003b, Smith and McKenzie 2004), infectivity success rate (Robert et al. 2003), infectivity index (Vercruysse et al. 1983), human susceptibility (Martens et al. 1999), proportion of suscessful inoculations (Beier et al. 1994) or proportion infective (Krafsur and Armstrong 1978).
cThe human-to-mosquito transmission efficiency, i.e. the proportion of mosquito bites on infectious humans which infect susceptible mosquitoes. Note the transmission-efficiency parameter is usually termed c in the literature. Since parameter c has not been officially termed various names are found in the literature, e.g. transmission efficiency (Smith and Mckenzie 2004) or mosquito infection probability (Burkot et al. 1990).
climateClimate represents an averaged weather which is observed over a long lasting period. In meteorology climate is classical defined via a 30 year climate normal period (e.g. 1961-1990).
climate changeThe term climate change refers to a statistically significant variation of the mean state or of its variability. This variations has to hold on for an extended period of a decade or even longer. A change in climate can be affected by natural causes or it can be triggered by human activity. In this study climate change can be attributed to enhanced human greenhouse gas emissions as well as alterations in the land vegetation cover.
climate suitability index of malariaThe climate suitability index of malaria is representing the suitability of temperature and rainfall conditions for the transmission of malaria. A value of 1 means that atmospheric condition is suitable for malaria transmission; a value of 0 means a unsuitable condition. Fractions from 0 to 1 indicate an increasingly suitable climate for malaria (cp. Craig et al. 1999).
degree-dayThe time needed to complete a temperature dependent process can be expressed in the term dd/(T-Ts). Here the "degree-day (dd)" is representing the accumulation of temperature units (T-Ts) over the time (e.g. if dd is 110 K and if (T-Ts) is 10 K, the process would last 11 days). At temperatures below the temperature threshold (Ts) the process is not accomplished.
EIRThe entomological inoculation rate is the number of infective mosquito bites received per person over a certain time period (typically a day, month or year).
endemicMalaria transmission is endemic, when the disease is constantly present to a greater or lesser degree in the population living in a particular location. Such populations usually acquire a certain level of disease immunity.
epidemicMalaria transmission is epidemic, when occasional malaria outbreaks occur in normally non-malaria regions. Because of low or no immunisation of such populations epidemics often cause high rates of mortality and morbidity. The malaria epidemic is spreading rapidly and is affecting many individuals in an area at the same time. Malaria studies also often refer epidemic malaria to unusual high seasonal transmission levels.
gametocytaemiaThe presence of gametocytes in the peripheral blood is called gametocytaemia. After the initial asexial wave gametocytes of Plasmodium falciparum arise after 7 to 15 days (Day et al. 1998; Diebner et al. 2000; Eichner et al. 2001).
gametocyteA gametocyte, either male or female, is a cell that is specialised in the transmission of the malaria parasite between humans and mosquitoes. Five different maturation stages of Plasmodium falciparum gametocytes are known (Talman et al. 2004).
gametocyte fractionThe fraction between humans carrying sexual malaria parasites (gametocytes) and humans carrying asexual parasites after the period during that gametocytogenesis would occur. Note, this parameter is not measured in malaria studies. However, parasitological studies measure the ratio between sexual and asexual parasite prevalence (see SAR), which is assumed to give roughly the save value as the gametocyte fraction.
gametocytogenesisAn asexual parasite goes through a series of changes, which will lead to the generation of a sexually competent parasite. The production of mature male and female gametocytes is termed gametocytogenesis (Talman et al. 2004).
greenhouse gasesAtmospheric gases which absorb and emit infrared terrestrial radiation at special given wavelengths. Primary greenhouse gases of the atmosphere are carbon dioxide, water vapour, nitrous oxide, methane and ozone. In climate scenarios the amount of greenhouse gases are changed as anticipated by the IPCC.
gonotrophic cycleThe gonotrophic cycle denotes the time for preparation of a brood in female Anopheles. It includes the development of eggs within the mosquito female as well as the time between the egg deposition and the blood meal of the mosquito female. The gonotrophic cycle primarily depends on temperature and, to a lesser degree, on external humidity.
HBIThe human blood index depicts the proportion of mosquito bites which are taken from humans.
hostA host is a human, animal or plant on which or in which another organism lives (e.g. a human which harbours the malaria parasite).
human infectious ageThe duration in days after that a human becomes infectious starting from the mosquito bite (cp. infectious human).
incidenceIn this study incidence is regarded as the daily number of new malaria infections (transmission of sporozoites from the mosquito vector to the human host) within a given population (e.g. 100 humans). Note, the 10-day-incidence is therefore the number of new infections within the last 10 days.
incubation periodThe incubation period is the time between infection and the appearance of symptoms of the disease (e.g. the period between the infective mosquito bite and occurrence of malaria fever).
infectious humanA necessary condition for the malaria transmission from a human host to a mosquito is the presence of male and female gametocytes in the host's blood. Under that condition a human is called infectious. However, gametocytes are not infectious for one to four days after their appearance and possibly not at the end of an infection if only macrogamteocytes are present (Nedelman 1989).
Note in this study a human infection means that the parasite is developing but the infectious stage is not obtained.
infectious mosquitoThe malaria parasite is transmitted from mosquitoes to humans by sporozoites. Female mosquitoes are infectious, when they are carrying sporozoites in their salivary glands.
By contrast in this study a malaria infection of a mosquito means that the parasite is developing to sporozoites in the mosquito.
infectedIn this study the term infected will mean infected with malaria parasites but not infectious to mosquitoes. On the other hand, when transmission is possible, the term infectious is used.
latent periodIn case of malaria the latent period represents the time between infection, i.e. when the mosquito transmits sporozoites on humans, and the moment when humans become infectious, i.e. when gametocytes have been developed in the human host.
malaria parasite cycleThe duration for the production of asexual parasites for Plasmodium falciparum, that are detectable by standard microscopy, lasts about two weeks (??). This process starts with the transmission of the malaria parasite from the female mosquito to a human via sporozoites. After the infection of a human sporozoites invade and reside within hepatocytes (liver cells). After several days sporozoites mature into schizonts, which rupture and release numerous merozoites. The merozoites enter the bloodstream and are infecting erythrocytes (red blood cells). The ring-cell stage trophozoites mature into schizonts, and produce again merozoites. The development of Plasmodium falciparum parasites within human red blood cells lasts 48 hours, at the end of which the parasitised red blood cells burst, liberating on average 16 merozoites (Eichner et al. 2001).
Blood stage parasites are responsible for clinical manifestations of the disease (Talman et al. 2004). The mature asexual stages of Plasmodium falciparum are mostly absent from the peripheral circulation. This is due to the sequestration of asexual parasites, i.e. the adherence of infected erythrocytes to microvascular endothelia of many organs and tissues such as heart, lung, liver, skin and brain (MacPherson et al. 1985). The process is often leading to a severe affection of the body (e.g. cerebral malaria). On the other hand bursting erythrocytes cause malaise and fever. A prolonged infection is sometimes leading to a severe anaemia.
The sexual stages of the parasite play a minor role in terms of morbidity, but an essential one for the transmission of the parasite. The production of the sexual form of the parasites starts when a successful merozoite invades another red blood cell and it either goes into another round of schizogony or develops male and female gametocytes. Maturing gametocytes are preferentially sequestered in the bone marrow and spleen (Thomson and Robertson 1935; Smalley et al. 1980). The maturation of gametocytes lasts about one week (Diebner et al. 2000; Eichner et al. 2001). The male and femal gametocytes are finally released in the circulation and can be picked up by an anopheline vector.
When the gametocytes are ingested by the mosquito vector, the so-called sporogonic cycle starts. Gametocytes first fuse within the gut and are generating zygotes. These zygotes become mobile and transform into elongated ookinetes. The ookinetes invade the midgut wall and turn into oocysts. Those oocysts increase in size, rupture and release sporozoites. The sporozoites finally reach the salivary glands and the life cycle of the malaria parasite is perpetuated.
morbidityMorbidity is defined as the rate of occurrence of disease within a population and given time period.
mortalityMortality is the rate of occurrence of death due to a disease within a population and time period.
mosquitoAccording to Reiter (2001) a mosquito is an insect of the family Culicidae and order Diptera (two-winged flies). Mosquitoes consist of about 3,500 species which lay their eggs into or in the vicinity of water. The egg, larvae and pupal stages are entirely aquatic. A salivary secretion serves as a vehicle for the transmission of pathogens such as malaria.
parasite ratioThe parasite ratio is the proportion of the survey population that is confirmed positive for the malaria parasite. Naturally, it is determined by taking standard thick and thin blood smear from volunteers, staining the slides with Giemsa, and examine the slides by a microscope (Beier et al. 1999). The malaria parasites are identified and counted canonical by immature ring stage trophozoites (Hay und Snow 2006).
person-monthPerson-months describe the number of people within a population group or geographic region multiplied with the number of malaria transmission month of a given year.
Plasmodium falciparumPlasmodium falciparum is one of the most important tropical monad, the causative agent of tropical malaria.
reproduction numberVarious classic malaria models are based on differential equations describing transmission potential. The equilibrium solutions of these equations are expressed via the basic reproduction number, which must equal at least 1 for disease persistence (Rogers and Randolph 2000).
scenarioA scenario is a description of the future state of e.g. climate or land cover. Scenarios are based upon observations of the past and try to extrapolate the actual trends into the future.
sporogonic cycleThe sporogonic cycle denotes the development of the malaria parasite to a stage that is transmittable from mosquitoes to humans. The cycle starts when a mosquito is receiving gametocytes from the human blood and it ends when sporozoites reach the salivary glands. The sporogonic cycle is governed by temperature and requires temperatures above a certain minimum temperature, the so-called sporogonic temperature threshold.
sporogonic temperature thresholdThe sporogonic temperature threshold is the minimum temperature needed to start the sporogonic cycle.
superinfectionA superinfection of malaria means that different infections proceed simultaneously (Gu et al. 2003). A given individual may receives more than one infective inoculation of parasites via multiple infectious bites (Anderson and May 1991).
vectorThe term vector denotes e.g. mosquitoes which are able to transfer the malaria parasite from infected humans to noninfected ones. The transfer includes the incubation period (the sporogonic cycle) in which the malaria parasite is proliferated and finally stored in the salivary glands.