Malaria Control During Mass Population Movements and Natural Disasters (2003) / Chapter Skim
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3. Epidemiology of Malaria
3. Epidemiology of Malaria
Pages 24-51
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From page 24... ...
The following section presents information on areas at risk of malaria transmission, the mechanics of how malaria is transmitted within a population, the range of clinical manifestations of malaria, antimalarial drug resistance, and the mosquito vector. The information presented is by no means exhaustive but should aid in basic decision making or in recognizing when expert assistance is needed.
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From page 25... ...
Duffy antigens, which are required by the parasite to invade red blood cells, are lacking in many ethnic groups, especially in West Africa. Vivax malaria, however, is the predominant species in Central America, most of malarious South America, and the Indian subcontinent (Miller et al., 19771.
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From page 27... ...
MALARIA VECTORS AND VECTOR BEHAVIOR Human malaria is transmitted by the bite of female mosquitoes belonging to the genus Anopheles. Of the 400 or so species of Anopheles in the world, approximately 60 are important vectors of malaria.
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28 MALARIA CONTROLDURINGMASSPOPULATIONMOVEMENTS TABLE 3-1 Characteristics of the Four Species of Human Malaria P? falcipar?
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MALARIA ILLNESS The normal incubation period from infective mosquito bite to onset of clinical symptoms is 9 to 30 days or longer, depending on such parameters as species of parasite, immune status, infecting dose, and use of antimalarial drugs. The clinical symptoms associated with malaria parasites are produced by increases in cytokines (particularly tumor necrosis factor)
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From page 30... ...
Although malaria prevalence in endemic areas decreases with increasing age, suggesting an acquired ability to clear malaria infections, immunity to malaria typically also involves the development of a tolerance for the presence of malaria parasites in the blood with a minimum of symptoms and relative protection from severe illness and death. EPIDEMIOLOGY OF CLINICAL MALARIA Malaria transmission intensity, levels of acquired immunity in a population, and manifestations of malaria illness are intimately linked (see Table 3-2; Snow et al., 1994; Slutsker et al., 19941.
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From page 31... ...
, mortality rates associated with malaria can be paradoxically low, probably due to high incidence of clinical symptoms, rapid treatmentseeking behavior of the population, and the high efficacy and ready availability of CQ. Examples: Central America, some parts of the Indian subcontinent, parts of Central Asia, parts of eastern Europe.
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From page 32... ...
MALAY DURING PREGNANCY Among nonimmune women, acute malaria during pregnancy carries a high risk of maternal and fetal death if not treated promptly and adequately. Among semiimmune pregnant women, however, malaria parasites preferentially sequester in the placenta, with minimal increase in overt clinical disease.
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From page 33... ...
ANTIMALARIAL DRUG RESISTANCE Simply defined, antimalarial drug resistance occurs when malaria parasites gain the ability to survive what should be an effective dose of antimalarial drugs. Resistance occurs because of naturally occurring mutations that affect the susceptibility of the parasite to a given drug.
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From page 45... ...
treatment failures, raise concern that this class of antimalarial drug is not "immune" to the development of resistance (Wongsrichanalai et al., 1999; Sahr et al.,20011. In many areas where population displacement occurs, national treatment policies of the host and source countries may not necessarily reflect the drug resistance patterns of a given region or population.
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From page 46... ...
In general, malaria parasites in western sub-Saharan Africa are less resistant to drugs like CQ and SP than malaria parasites in eastern or southern Africa. In Southeast Asia the distribution of drug resistance is highly variable and focal.
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From page 47... ...
In situations where breeding sites are small, dispersed, or not easily identified, however, larval control would be inappropriate. As mentioned previously, some malaria vectors (such as An.
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From page 48... ...
F FIR N F R N F F F HAL, ON F F F Resistan South A Border resistant variable Greatest transmit NOTES: Reports of resistance to a given agent occurring in an area do not necessarily mean that occurrence is frequent enough to pose a significant public health risk. "F" indicates agents to which frequent resistance occurs in a given area (although actual risk may be highly focal e.g., Southeast Asia, where MQ resistance, while very frequent in
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From page 49... ...
"N" indicates that resistance has not been reported to date or occurs at a rate low enough to not present a substantial public health threat.
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