Annual variations in the number of malaria cases related to two different patterns of Anopheles darlingi transmission potential in the Maroni area of French Guiana

Abstract

BackgroundWith an Annual Parasite Incidence (API) of 132.1, in the high and moderate risks zones, the Maroni area of French Guiana has the second highest malaria incidence of South-America after Guyana (API = 183.54) and far above Brazil (API = 28.25). Malaria transmission is occurring despite strong medical assistance and active vector control, based on general WHO recommendations. This situation is generated by two main factors that are the social and cultural characteristics of this border area, where several ethnic groups are living, and the lack of understanding of transmission dynamics of the main mosquito vector, Anopheles darlingi. In this context, entomological data collected in two villages belonging to two different ethnic groups of the French border of the Maroni River, were retrospectively analysed to find out how the mosquito bionomics are related to the malaria transmission patterns.MethodsData were provided by human landing catches of mosquitoes carried out each month for two years in two villages belonging to two ethnic groups, the Amerindians Wayanas and the Aloukous of African origin. The mosquitoes were sorted by species, sex, date, hour and place of collection and processed for Plasmodium sp. parasite detection. The data were compiled to provide the following variables: human biting rates (HBR), parity rates (PR), numbers of infective bites (IB), entomological inoculation rates (EIR) and numbers of infected mosquitoes surviving enough to transmit (IMT). Spatial and temporal differences of variables between locations and during the night were tested by the Kruskall-Wallis analysis of variance to find out significant variations.ResultsThe populations of the main mosquito vector An. darlingi showed significant variations in the spatial and temporal HBR/person/night and HBR/person/hour, IB/person/month and IB/person/hour, and IMT/village/night and IMT/village/hour. In the village of Loca (Aloukous), the IMT peaked from June to August with a very low transmission during the other months. The risks were higher during the first part of the night and an EIR of 10 infective bites per person and per year was estimated. In the village of Twenke (Wayanas), high level of transmission was reported all year with small peaks in March and October. The risk was higher during the second part of the night and an EIR of 5 infective bites per person and per year was estimated.ConclusionFor the first time in the past 40 years, the mosquito bionomics was related to the malaria transmission patterns in French Guiana. The peak of malaria cases reported from August to October in the Maroni region is concomitant with the significant peak of An. darlingi IMT, reported from the village of Loca where transmission is higher. However, the persistent number of cases reported all year long may also be related to the transmission in the Amerindian villages. The An. darlingi bionomics for these two close populations were found significantly different and may explain why a uniform vector control method is inadequate. Following t...

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

“…As suggested by Moreno et al (2007) and Fouque et al (2010), it seems probable that the longevity of An. darlingi populations may play an important role in malaria-transmission dynamics in certain situations.…”

“…Previous research on An. darlingi bionomics and malarial transmission dynamics in French Guiana has focused on Surinamese and French villages along the Maroni riverbecause of the high incidence of malaria historically reported in such communities (Hudson, 1984;Rozendaal, 1992;Girod et al, 2008;Fouque et al, 2010;Hiwat et al, 2010). The results have allowed the risks of malarial transmission along the Maroni river to be estimated but most of the contributory factors, such as the bionomics and behavioural characteristics of the An.…”

Incrimination of Anopheles (Anopheles) intermedius Peryassú, An. (Nyssorhynchus) nuneztovari Gabaldón, An. (Nys.) oswaldoi Peryassú as natural vectors of Plasmodium falciparum in French Guiana

“…darlingi was collected in high densities, had a high sporozoite index and was the only species naturally infected by the four Plasmodium sp. and variants, especially along the border with suriname in the Maroni valley (Girod et al 2008, Hiwat et al 2009, Fouque et al 2010). In our study, specimens of this species infected by P. vivax were found along the Oyapock River, where this parasite causes most cases of malaria (Carme et al 2009, Girod et al 2011, whereas the other anophelines carried P. falciparum.…”

Confirmation of the Occurrence of Anopheles (Nyssorhynchus) Marajoara in French Guiana

“…marajoara reference specimens. Since then extensive studies have been conducted along the littoral and the main inland rivers of French Guiana, but no member of Albitarsis Complex has ever been collected (Fauran 1961, Fauran and Pajot 1974, Pajot et al 1978, Degallier and Claustre 1980, Claustre et al 2001, Girod et al 2008, Hiwat et al 2009, Fouque et al 2010, Girod et al 2011, Dusfour et al 2012.…”