Rift Valley fever vector diversity and impact of meteorological and environmental factors on Culex pipiens dynamics in the Okavango Delta, Botswana

BACKGROUND : 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. 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. METHODS : Using 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). RESULTS : More 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. CONCLUSIONS : Our 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.Additional file 1: Serological analysis (Sampling strategy, laboratory analysis and results).Additional file 2: Mapping flooding extent method. Figure in Additional file 2. Maps of Modified Normalized Difference Water Index (MNDWI) derived from MODIS imagery at different dates corresponding to the study period.Additional file 3 Detail of the ordinary differential equation system.Funding was provided by FAO. Award Number: LoA OSRO/INT/602/USA/B1.http://www.parasitesandvectors.comam2016Zoology and Entomolog

The sequential aerosol technique : a major component in an Iitegrated strategy of intervention against riverine Tsetse in Ghana

An integrated strategy of intervention against tsetse flies was implemented in the Upper West Region of Ghana (9.62u–11.00u N, 1.40u–2.76u W), covering an area of <18,000 km2 within the framework of the Pan-African Tsetse and Trypanosomosis Eradication Campaign. Two species were targeted: Glossina tachinoides and Glossina palpalis gambiensis. METHODOLOGY/PRINCIPAL FINDINGS: The objectives were to test the potentiality of the sequential aerosol technique (SAT) to eliminate riverine tsetse species in a challenging subsection (dense tree canopy and high tsetse densities) of the total sprayed area (6,745 km2) and the subsequent efficacy of an integrated strategy including ground spraying (<100 km2), insecticide treated targets (20,000) and insecticide treated cattle (45,000) in sustaining the results of tsetse suppression in the whole intervention area. The aerial application of low-dosage deltamethrin aerosols (0.33–0.35 g a.i/ha) was conducted along the three main rivers using five custom designed fixed-wings Turbo thrush aircraft. The impact of SAT on tsetse densities was monitored using 30 biconical traps deployed from two weeks before until two weeks after the operations. Results of the SAT monitoring indicated an overall reduction rate of 98% (from a pre-intervention mean apparent density per trap per day (ADT) of 16.7 to 0.3 at the end of the fourth and last cycle). One year after the SAT operations, a second survey using 200 biconical traps set in 20 sites during 3 weeks was conducted throughout the intervention area to measure the impact of the integrated control strategy. Both target species were still detected, albeit at very low densities (ADT of 0.27 inside sprayed blocks and 0.10 outside sprayed blocks). CONCLUSIONS/SIGNIFICANCE: The SAT operations failed to achieve elimination in the monitored section, but the subsequent integrated strategy maintained high levels of suppression throughout the intervention area, which will contribute to improving animal health, increasing animal production and fostering food security.The work was funded by the Pan-African Tsetse and Trypanosomosis Eradication Campaign/Ghana and the International Fund for Agricultural Development (IFAD) (project GCP/RAF/442/IFA).http://www.plosntds.org /home.actionam2013ab201

Additional file 2: of Rift Valley fever vector diversity and impact of meteorological and environmental factors on Culex pipiens dynamics in the Okavango Delta, Botswana

Mapping flooding extent method. Figure in Additional file 2. Maps of Modified Normalized Difference Water Index (MNDWI) derived from MODIS imagery at different dates corresponding to the study period. (PDF 3185 kb

Results of the entomological survey conducted in Ghana one year after SAT operations.

<p>The survey was conducted from 6^th to 24th June 2011to monitor the impact of the integrated tsetse control campaign. Tsetse apparent density is expressed as the number of catches per trap per day.</p

Timeline of the preparation and implementation of the integrated intervention strategy against riverine tsetse.

<p>For field operations the bars indicate the start and end date of deployment. More details on the spatial configuration and the frequency of deployment are provided in the text.</p

Tsetse control operations conducted in the Upper West Region of Ghana.

<p>The map represents the situation from March 2010 to December 2011.</p

Temperatures inversion layer measured from Wa airport on 2 April 2010.

<p>Temperatures inversion layer measured from Wa airport on 2 April 2010.</p

Mean daily catch of tsetse before and during the SAT operation in Ghana.

<p>Vertical bars indicate the periods of SAT applications.</p