Unravelling the relationships between Anopheles darlingi (Diptera: Culicidae) densities, environmental factors and malaria incidence: understanding the variable patterns of malarial transmission in French Guiana (South America)

Abstract

Anopheles darlingi, one of the main malaria vectors in the Neotropics, is widely distributed in French Guiana, where malaria remains a major public-health problem. Elucidation of the relationships between the population dynamics of An. darlingi and local environmental factors would appear to be an essential factor in the epidemiology of human malaria in French Guiana and the design of effective vector-control strategies. In a recent investigation, longitudinal entomological surveys were carried out for 2-4 years in one village in each of three distinct endemic areas of French Guiana. Anopheles darlingi was always the anopheline mosquito that was most frequently caught on human bait, although its relative abundance (as a proportion of all the anophelines collected) and human biting rate (in bites/person-year) differed with the study site. Seasonality in the abundance of human-landing An. darlingi (with peaks at the end of the rainy season) was observed in only two of the three study sites. Just three An. darlingi were found positive for Plasmodium (either P. falciparum or P. vivax) circumsporozoite protein, giving entomological inoculation rates of 0·0-8·7 infectious bites/person-year. Curiously, no infected An. darlingi were collected in the village with the highest incidence of human malaria. Relationships between malaria incidence, An. darlingi densities, rainfall and water levels in the nearest rivers were found to be variable and apparently dependent on land-cover specificities that reflected the diversity and availability of habitats suitable for the development and reproduction of An. darlingi.

Figure 1

A map showing the locations of the Camopi, Apatou and Régina mosquito-collection sites and the meteorological and limnimetric stations close to them.

Figure 2

In these three graphs, the bars show Anopheles darlingi human biting rates at the Camopi study site while the lines show rainfall at Camopi (a), maximum river levels at Saut Maripa (b), and the number of malaria cases presenting at the Camopi health centre (c).

Figure 3

In these three graphs, the bars show Anopheles darlingi human biting rates in Midenangalanti and Bois Martin while the lines show rainfall at Apatou (a), maximum river levels at Langatabiki (b), and the number of malaria cases presenting at the Apatou health centre (c).

Figure 4

In these three graphs, the bars show Anopheles darlingi human biting rates in ‘Village Inéri’ (Régina) while the lines show rainfall at Régina (a), maximum river levels at Saut Athanase (b), and the number of malaria cases presenting at the Régina health centre (c).

Figure 5

Percentage of each land-cover class, as a function of buffer size, at the study sites of Camopi (▪), Régina (▴) and Apatou (•).

Figure 6

Lengths of river bank within the Camopi (▪), Régina (▴) and Apatou (•) study sites, as a function of buffer size.