Abstract
BackgroundIn Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes cohabitate around permanent waters of the Okavango Delta. As in other regions of sub-Saharan Africa, Rift Valley Fever (RVF) virus is known to circulate in that area among wild and domestic animals. However, the diversity and composition of potential RVF mosquito vectors in that area are unknown as well as the climatic and ecological drivers susceptible to affect their population dynamics.MethodsUsing net traps baited with carbon dioxide, monthly mosquito catches were implemented over four sites surrounding cattle corrals at the northwestern border of the Okavango Delta between 2011 and 2012. The collected mosquito species were identified and analysed for the presence of RVF virus by molecular methods. In addition, a mechanistic model was developed to assess the qualitative influence of meteorological and environmental factors such as temperature, rainfall and flooding levels, on the population dynamics of the most abundant species detected (Culex pipiens).ResultsMore than 25,000 mosquitoes from 32 different species were captured with an overabundance of Cx. pipiens (69,39 %), followed by Mansonia uniformis (20,67 %) and a very low detection of Aedes spp. (0.51 %). No RVF virus was detected in our mosquito pooled samples. The model fitted well the Cx. pipiens catching results (ρ = 0.94, P = 0.017). The spatial distribution of its abundance was well represented when using local rainfall and flooding measures (ρ = 1, P = 0.083). The global population dynamics were mainly influenced by temperature, but both rainfall and flooding presented a significant influence. The best and worst suitable periods for mosquito abundance were around March to May and June to October, respectively.ConclusionsOur study provides the first available data on the presence of potential RVF vectors that could contribute to the maintenance and dissemination of RVF virus in the Okavango Delta. Our model allowed us to understand the dynamics of Cx. pipiens, the most abundant vector identified in this area. Potential predictions of peaks in abundance of this vector could allow the identification of the most suitable periods for disease occurrence and provide recommendations for vectorial and disease surveillance and control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1712-1) contains supplementary material, which is available to authorized users.
Highlights
In Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes cohabitate around permanent waters of the Okavango Delta
It should be noticed that a very low number of Aedes (Aedes) was detected (4 species including 134 individuals) mostly represented by Ae. (Neomelaniconion) mcintoshi and Ae. (Neomelaniconion) unidentatus. Despite all these species being able to transmit Rift Valley fever virus (RVFV) [45, 46], no evidence of RVFV or other arboviruses was found in the mosquito pools inoculated to mice
In this paper, we provide original data describing, for the first time, the diversity of mosquito populations in the region of Okavango Delta in northern Botswana where RVFV is suspected to circulate without reports of clinical outbreaks
Summary
In Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes cohabitate around permanent waters of the Okavango Delta. As in other regions of sub-Saharan Africa, Rift Valley Fever (RVF) virus is known to circulate in that area among wild and domestic animals. Transmitted to vertebrates by mosquitoes, mainly of the genera Culex and Aedes, or direct contact with viraemic animal products, it is responsible for Rift Valley fever (RVF), an acute disease considered as a significant global threat to both humans and animals [3, 4]. RVF, which significantly affects the health of animals and/or humans, induces a very heavy economic impact in the societies where it is present, and in developing countries of tropical and sub-tropical areas [10]. In Botswana, as in other regions of subSaharan Africa, RVF virus is suspected to circulate among animals without reports of clinical outbreaks [11]. Each mosquito species requires specific environmental conditions to develop and survive, such as water availability to lay eggs, optimal temperature for aquatic stage development, limited wind (to facilitate hostseeking or breeding-site-seeking behaviour), or specific vegetation for some species [16]
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