Deforestation and vectorial capacity of Anopheles gambiae Giles mosquitoes in malaria transmission, Kenya.
Bottom Line: Deforested sites had higher temperatures and relative humidities, and the overall infection rate of mosquitoes was increased compared with that in forested sites.Sporozoites appeared on average 1.1 days earlier in deforested areas.Vectorial capacity was estimated to be 77.7% higher in the deforested site than in the forested site.
Affiliation: Kenya Medical Research Institute, Kisumu, Kenya.
We investigated the effects of deforestation on microclimates and sporogonic development of Plasmodium falciparum parasites in Anopheles gambiae mosquitoes in an area of the western Kenyan highland prone to malaria epidemics. An. gambiae mosquitoes were fed with P. falciparum-infected blood through membrane feeders. Fed mosquitoes were placed in houses in forested and deforested areas in a highland area (1,500 m above sea level) and monitored for parasite development. Deforested sites had higher temperatures and relative humidities, and the overall infection rate of mosquitoes was increased compared with that in forested sites. Sporozoites appeared on average 1.1 days earlier in deforested areas. Vectorial capacity was estimated to be 77.7% higher in the deforested site than in the forested site. We showed that deforestation changes microclimates, leading to more rapid sporogonic development of P. falciparum and to a marked increase of malaria risk in the western Kenyan highland.
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Mentions: The number of oocysts in a mosquito ranged from 1 to 98. The proportion of mosquitoes that carried P. falciparum infection (either oocysts or sporozoites) differed significantly among the sites (F2,30 = 12.1, p<0.0001) (Figure 2, panel A), and post hoc contrast indicated a significant forested–deforested difference within the highland site (F1,30 = 16.5, p<0.0001). Mean oocyst intensity was affected by land use type (F2,30 = 6.5, p<0.01) (Figure 2, panel B). Time for sporozoite development differed between sites (F2,13 = 9.1, p<0.01), and post hoc contrasts indicated a significant difference between forested and deforested areas in the highland site (F1,13 = 6.9, p<0.05) (Figure 2, panel C), and the lowland site exhibited the shortest sporozoite development time. Post hoc contrasts did not result in different conclusions from the alternative approach of reducing the number of factor levels in the dataset (e.g., comparing forested with deforested sites in the absence of lowland data).