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Malaria transmission patterns
11/8/04. By Caroline Cross
The transmission of malaria involves many types of mosquito, complicating the picture of human infection and disease.
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Malaria is transmitted between people by mosquitoes, and more than 60 species have been incriminated in the transmission of infection. Some species are more significant than others as vectors because of variations in susceptibility to the parasite or the propensity of the mosquito to bite humans and to enter houses when looking for a blood meal. Anopheles gambiae sensu lato is the
vector of most significance in Africa.
The local form(s) of the vector are an important determinant of the transmission dynamics of infection. Together with the local climatic conditions, this can have profound effects on how malaria impacts on the human population. In many areas, successive infections with malaria occur repeatedly from birth. This regular exposure leads to the acquisition of a level of immunity
against the more severe outcomes of infection. But nature's 'vaccine' is paid for by an unacceptable level of infant and childhood mortality.
Where exposure to infection is more sporadic, the clinical manifestations of malaria are more evenly spread across age-groups and epidemics may occur.
Table 1
Malaria transmission patterns
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Stable malaria transmission
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Unstable malaria transmission
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Immunity in adults
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High
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Low
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Clinical manifestations
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Primarily in young children and pregnant women
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Affecting all ages
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Local mosquito species
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Efficient vectors
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Inefficient vectors
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Main parasite
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Plasmodium falciparum
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Usually Plasmodium vivax
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Climate
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Favourable for rapid development in mosquito
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Not favourable for rapid development in mosquito
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Level of transmission
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Moderate to very high
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Low (high when epidemic)
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Seasonal changes in incidence
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Not very pronounced - possibly short dry season
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Pronounced
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Fluctuations in incidence
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Not marked - related to seasons
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Very marked
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Epidemics
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Unlikely in the indigenous population
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Likely when climatic conditions suitable
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End the table here
Page of 2; 2/9/04
[WTD023873] Malaria transmission patterns.doc
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