Vectors and environmental factors in malaria

Malaria is a major risk for more than two billion human beings on Earth, an d is the cause of 700,000 to 2.5 million deaths per year. The causative fac tor, Plasmodium (four species), involves an asexual cycle in man and a sexu al one in anopheline mosquitoes. The four species of Plasmodium are pathoge nic for man but P. falciparum accounts for more than 90% of deaths. Only bl ack Africans are refractory to P. vivax, a characteristic Linked to the lac k of Duffy antigen. Among the 400 species of anophelines so far recorded, l ess than 50 are recognized malaria vectors. Every one has its own geographi c and ecological characteristics, which locally induce the epidemiological trends and its biodiversity. In a given site transmission depends on compet ent anopheline species, their infective rate and their biting rate. Inhabit ants of endemic areas develop during infancy immunity which protect them du ring the rest of their Lives. This immunity (premunition) between parasite and its host is acquired at an heavy price of infant mortality. It can decr ease rapidly when people leave endemic areas. Because inhabitants of endemi c areas continue to harbor asymptomatic parasites they become good parasite reservoirs. The diversity of epidemiological situations needs a diversific ation of malaria control measures. The prognosis of the evolution of malaria depends on control measures, appl ied or not, and on the evolution of climatic and anthropic environment, whi ch are very hard to predict for the time being. (C) 1999 Elsevier, Paris.