Spatial and Temporal Heterogeneity of Anopheles Mosquitoes and Plasmodium Falciparum Transmission Along the Kenyan Coast

Abstract

The seasonal dynamics and spatial distributions of Anopheles mosquitoes and Plasmodium falciparum parasites were studied for one year at 30 villages in Malindi, Kilifi, and Kwale Districts along the coast of Kenya. Anopheline mosquitoes were sampled inside houses at each site once every two months and malaria parasite prevalence in local school children was determined at the end of the entomologic survey. A total of 5,476 Anopheles gambiae s.l. and 3,461 An. funestus were collected. Species in the An. gambiae complex, identified by a polymerase chain reaction, included 81.9% An. gambiae s.s., 12.8% An. arabiensis, and 5.3% An. merus. Anopheles gambiae s.s. contributed most to the transmission of P. falciparum along the coast as a whole, while An. funestus accounted for more than 50% of all transmission in Kwale District. Large spatial heterogeneity of transmission intensity (< 1 up to 120 infective bites per person per year) resulted in correspondingly large and significantly related variations in parasite prevalence (range ‫ס‬ 38−83%). Thirty-two percent of the sites (7 of 22 sites) with malaria prevalences ranging from 38% to 70% had annual entomologic inoculation rates (EIR) less than five infective bites per person per year. Anopheles gambiae s.l. and An. funestus densities in Kwale were not significantly influenced by rainfall. However, both were positively correlated with rainfall one and three months previously in Malindi and Kilifi Districts, respectively. These unexpected variations in the relationship between mosquito populations and rainfall suggest environmental heterogeneity in the predominant aquatic habitats in each district. One important conclusion is that the highly non-linear relationship between EIRs and prevalence indicates that the consistent pattern of high prevalence might be governed by substantial variation in transmission intensity measured by entomologic surveys. The field-based estimate of entomologic parameters on a district level does not provide a sensitive indicator of transmission intensity in this study.

Concentración de los anticuerpos en contra de proteínas de las glándulas salivares de Aedes aegypti e historia de la exposición al virus del dengue en residentes de una zona endémica colombiana

“…Consequently, it was not possible to test for DENV infection/viremia, which are important to determine both the timing and order of exposure (36). Second, previous studies have shown that entomological parameters, such as the human biting rate, can vary within small geographical areas (37) and that factors that affect individual attractiveness to mosquitoes should be also taken into account (38). We are currently recruiting a larger study population in the same three areas of Norte de Santander to address these issues.…”

Force of infection is key to understanding the epidemiology ofPlasmodium falciparummalaria in Papua New Guinean children

“…On the Kenyan coast, locally estimated EIRs were found to be only weakly or not associated with prevalence of infection (17,18) or incidence of severe disease (17). Except for areas with very low EIR, saturation in the infection rate with increasing transmission was reported from Tanzania and Senegal (19,20).…”

Parasite sources and sinks in a patched Ross–Macdonald malaria model with human and mosquito movement: Implications for control

“…Human and mosquito populations are often spatially clustered [24], causing malaria risk to be heterogeneous across spatial scales [16,6]. Host mediated parasite movement on these landscapes drives source-sink parasite dynamics which elimination programs must account for [9], as areas with enough transmission to sustain parasite populations locally will export excess parasites through host movement, known as transmission foci, supporting parasite populations in sink areas, or areas where parasites would not persist otherwise [9].…”