Saving Lives, Buying Time Economics of Malaria Drugs in an Age of Resistance (2004) / Chapter Skim
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6 The Parasite, the Mosquito, and the Disease
6 The Parasite, the Mosquito, and the Disease
Pages 136-167
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From page 136... ...
Plasmodium vivax, which is prevalent in temperate as well as tropical and subtropical zones, has the widest geographical range because it can survive at lower temperatures within a mosquito than the other three parasites that infect humans. Plasmodium falciparum, the most lethal strain, is the most prevalent species throughout the tropics and subtropics.
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Plasmodium ovale is found in tropical Africa, and occasionally in Asia and the western Pacific. Biologic and Genetic Diversity One of the remarkable features of human plasmodia is their biology, which allows these small yet genetically complex microbes to survive and exploit several different environments: the liver and blood cells of humans as well as the gut, vascular system, and salivary glands of mosquitoes.
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falciparum schizonts attach to blood vessels in the brain, cerebral malaria can result (Adams et al., 2002) , while in the placenta, adherent schizonts may reduce fetal blood supply and thus contribute to impaired fetal growth (Scherf et al., 2001)
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Chronically Infected Humans and Malaria Transmission In order to sustain malaria transmission, new female anophelines must be continuously infected. This requires a human reservoir containing abundant circulating gametocytes.
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contained in the liver. Plasmodium falciparum and P
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nets (ITNs) offer little protection against malaria infection.
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argyritarsis A.(A.) aztecus the South American A.(N.)
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THE PARASITE, THE MOSQUITO, AND THE DISEASE 143 TABLE 6-1 Continued Main Local or Zone Extension Malaria Vectors Secondary Vectors A.(C.) tesselatus 9 Indo-Chinese A triangular area A.(C.)
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have developed mathematical models of malaria transmission which attempt to correlate human infection with the prevalence of malaria infection in mosquitoes. The entomologic inoculation rate (EIR)
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. There is, however, a shift from severe malarial disease in children younger than 5 years toward severe disease in older age groups when entomological inoculation rates fall below 10 to 20 bites per year (Snow et al., 1997)
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. Subclinical Infections in Areas of Stable Transmission New evidence for chronic, subpatent malaria infection in areas of stable transmission has recently come from studies employing highly sensitive polymerase chain reaction (PCR)
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CLINICAL FEATURES OF FALCIPARUM MALARIA Falciparum malaria gives rise to a broad spectrum of disease from asymptomatic infection to fatal syndromes such as cerebral malaria, severe anemia, and multi-organ failure. The principal determinant of outcome is the immune status of the infected patient.
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, anemia develops within days of the initial paroxysm. Additional clinical features and/or laboratory findings predictive of a "severe" or life-threatening course are prostration, shock, altered consciousness, respiratory distress (from acidotic breathing or pulmonary edema)
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Transactions of the Royal Society of Tropical Medicine and Hygiene. 94 (suppl 1)
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. Common hallmarks of severe malaria in African children are altered consciousness, convulsions, hypoglycemia, acidosis, and anemia.
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Third, low birth weight -- frequently the consequence of malaria infection in pregnant women -- is the major risk factor for death in the first month of life. WHO, Africa Malaria Report, 2003 Children with severe anemia tend to be younger than those with cerebral malaria, but the two conditions often overlap.
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Irene Agyepong, Ghana Health Service (2002) African children with cerebral malaria usually enter a coma following a 1- to 3-day history of fever.
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. Epilepsy and EEG abnormalities following cerebral malaria have probably been underestimated in past studies; recent data suggest that the relative risk of epileptic discharges following cerebral malaria or malaria plus seizures is increased nearly twofold compared to children who have not suffered severe malaria (Otieno et al., 2002)
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Whereas children are more likely to develop severe anemia, hypoglycemia, or convulsions, adults with severe malaria are more likely to develop jaundice, acute kidney damage, or acute pulmonary edema. Recovery from cerebral malaria in adults is slower than in children although neurologic sequelae are less frequent (occurring in less than 3 percent of adult cases compared with 10 percent of pediatric cases)
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. Complications to which pregnant malaria-infected women with low immunity are especially susceptible include high fever, low blood sugar, severe hemolytic anemia, cerebral malaria, and pulmonary edema (Looareesuwan et al., 1985)
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, and two studies found higher death rates due to severe malaria in HIV-1 positive adults (Leaver et al., 1990; Niyongabo et al., 1994)
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. NON-FALCIPARUM MALARIA Plasmodium vivax Plasmodium vivax malaria is widely distributed throughout the world-predominantly in Asia, the Western Pacific, and the Americas -- and accounts for over half of all malaria infections outside Africa, and roughly 10 percent of infections in Africa (Mendis et al., 2001)
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vivax malaria on pregnancy, although some investigators have linked it to maternal parasitemia and anemia, as well as low birth weight (Nosten et al., 1999; Singh et al., 1999)
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American Journal of Tropical Medicine and Hygiene 66(3)
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American Journal of Tropical Medicine and Hygiene 67(3)
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American Journal of Tropical Medicine and Hygiene 56(5)
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American Journal of Tropical Medicine and Hygiene 66(1)
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falciparum malaria in African children with a proposed classification and grading sys tem. Transactions of the Royal Society of Tropical Medicine and Hygiene 93(6)
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American Journal of Tropical Medicine and Hygiene 26(6 Pt 2)
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American Journal of Tropical Medicine and Hygiene 65(5)
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American Journal of Tropical Medicine and Hygiene 31(1)
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1987. Hypoglycaemia in African children with severe malaria.
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