Vectorial capacities for malaria in eastern Amazonian Brazil depend on village, vector species, season, and parasite species

Abstract

Background The vector species in the Amazon River Basin are regionally and locally diverse, which makes it imperative to understand and compare their roles in malaria transmission to help select appropriate methods of intervention and evaluation. The major aim of this study was to measure the vectorial capacity of five Anopheles species in three neighbouring villages, for two Plasmodium parasite species affecting humans. Methods From 32 consecutive months of sampling in three villages, 1.5–7.0 km apart, on the Matapi River, Amapá State, Brazil, vectorial capacities (C) were estimated as time series for An. darlingi, An. marajoara, An. nuneztovari, An. triannulatus, and An. intermedius. Monthly parity measurements for each vector species were used to estimate daily survivorship and compared to estimates of survivorship from mark-release-recapture experiments. Gonotrophic cycle lengths were estimated through a time-series analysis of parity data, and durations of sporogony at study site temperatures for the two malaria parasite species were estimated from previous literature. Results The absolute abundances of five vector species were strongly tracked by the spatial variation in C among villages. Temporally, C varied between wet and dry seasons, with An. darlingi, An. marajoara and An. triannulatus exhibiting higher C in the dry season from August to December, and An. nuneztovari its highest C early in the rainy season in January and February. Anopheles intermedius exhibited higher C in the rainy season from April to June than in the dry season. Significant differences in overall survival for each independent variable, and a significant difference in C between wet and dry seasons, among villages, and among vector species for both Plasmodium falciparum and Plasmodium vivax. A generalized linear mixed model (GLMM) analysis by village showed significant effects of vector species on C in only one village, but significant effects of parasite species in all three. Although the GLMM analysis detected no significant parasite x vector species interaction effects on C, effects on C of spline regressions of C dynamics x vector species interactions were significant in all villages. Conclusions These detailed analyses of entomological and parasitological variables revealed hidden complexities of malaria epidemiology at local scales in neighbouring riverine villages of the Amazon Region.

Optimizing malaria vector control: A systematic review and mathematical modelling study to identify desirable characteristics of novel tools in different settings

“…Previous vectorial capacity modelling studies have been summarised by Catano-Lopez et al [19]. These studies have taken into account some of these factors: the ability of mosquitoes to transmit a pathogen after exposure (known as vector competence) [84,85], age-dependent vector mortality [86][87][88], or temperature related transmission parameters [89][90][91][92]. To extend our model, a comprehensive review of these factors is recommended.…”

Bionomics and population dynamics of anopheline larvae from an area dominated by fish farming tanks in northern Brazilian Amazon

“…In Brazil, ~99.7% of human malaria cases occur in the Amazon rainforests, where the transmission occurs mainly by Plasmodium vivax (>90%) [1]. The complex environment of the Amazon rainforests favors the development of mosquito populations, which is directly associated with the annual flood cycle and river flow regimes [1,2]. This pattern allied to the tropical climate of the region, among other factors, favors the high density of anopheline mosquitoes [1][2][3].…”

“…The complex environment of the Amazon rainforests favors the development of mosquito populations, which is directly associated with the annual flood cycle and river flow regimes [1,2]. This pattern allied to the tropical climate of the region, among other factors, favors the high density of anopheline mosquitoes [1][2][3].…”

“…From January to June 2019, these municipalities contributed to approximately 54% of the malaria cases in the state and approximately 43% in the same period of 2020 [4]. This scenario can be attributed to the high density of the main malaria vector, Anopheles darlingi [2,[5][6][7][8]. In addition, entomological investigations conducted in Amapa ´have reported the association of Anopheles marajoara and Anopheles nuneztovari s.l.…”

“…In addition, entomological investigations conducted in Amapa ´have reported the association of Anopheles marajoara and Anopheles nuneztovari s.l. with malaria transmission [2,[7][8][9], contributing to the complexity of the malaria transmission patterns in the region. Further investigations on the vector composition in Amapa ´can help implement appropriate methods of intervention.…”