Zika virus in southeastern Senegal: survival of the vectors and the virus during the dry season

Abstract

Background: Zika virus (ZIKV, genus Flavivirus, family Flaviviridae) is transmitted mainly by Aedes mosquitoes. This virus has become an emerging concern of global public health with recent epidemics associated to neurological complications in the pacific and America. ZIKV is the most frequently amplified arbovirus in southeastern Senegal. However, this virus and its adult vectors are undetectable during the dry season. The aim of this study was to investigate how ZIKV and its vectors are maintained locally during the dry season.

Methods: Soil, sand, and detritus contained in 1339 potential breeding sites (tree holes, rock holes, fruit husks, discarded containers, used tires) were collected in forest, savannah, barren and village land covers and flooded for eggs hatching. The emerging larvae were reared to adult, identified, and blood fed for F1 production. The F0 and F1 adults were identified and tested for ZIKV by Reverse Transcriptase-Real time Polymerase Chain Reaction.

Results: A total of 1016 specimens, including 13 Aedes species, emerged in samples collected in the land covers and breeding sites investigated. Ae. aegypti was the dominant species representing 56.6% of this fauna with a high plasticity. Ae. furcifer and Ae. luteocephalus were found in forest tree holes, Ae. taylori in forest and village tree holes, Ae. vittatus in rock holes. ZIKV was detected from 4 out of the 82 mosquito pools tested. Positive pools included Ae. bromeliae (2 pools), Ae. unilineatus (1 pool), and Ae. vittatus (1 pool), indicating that the virus is maintained in these Aedes eggs during the dry season.

Conclusion: Our investigation identified breeding sites types and land cover classes where several ZIKV vectors are maintained, and their maintenance rates during the dry season in southeastern Senegal. The maintenance of the virus in these vectors in nature could explain its early amplification at the start of the rainy season in this area.

Keywords: Aedes; Eggs; Local maintenance; Southeastern Senegal; Vertical transmission; Zika virus.

Fig. 1

Map showing different Aedes egg sampling sites in the Kédougou in December 2015, October 2016 and March 2017. Insets are obtained from ArcGIS Desktop V 10.5 (ESRI 2019, Redlands, CA: Environmental Systems Research Institute; https://desktop.arcgis.com/en/); sampling sites are placed on base map using their respective XY coordinates and ArcGIS Desktop. Base map was obtained from Google earth: Google earth V 7.3.2.5776. (December 14, 2015). Kedougou, Senegal, Image© 2019 Maxar Technologies, Image© 2019 CNES / Airbus, US Dept of State Geographer, http://www.earth.google.com [April 17, 2019]