First Record of an Aedes Species Mosquito in North-Western Province of Zambia? Observation during a Yellow Fever Risk Assessment Survey

IntroductionStudies on Aedes species distribution, bionomics and species composition in Zambia are limited and systematic reports date back to 1950s. Mosquito vector studies have tended to focus on vectors of malaria (1, 2). Malaria is ranked among the top ten common causes of illness in the country. In 2013, during a yellow fever risk assessment survey, an entomological survey was conducted to ascertain the availability, density and infectivity of yellow fever vectors in North-Western province of Zambia.MethodsThe study was conducted in North-Western province of Zambia in six districts, namely, Mwinilunga, Mufumbwe, Kabompo, Chavuma, Solwezi and Zambezi. North-Western province is located at 1,354 metres above sea level, latitude -13.0 and longitude 25.0 and has a population of 706,462. The province borders with Angola on the western side and the Democratic Republic of Congo on the northern side. Highest rainfall in the country, with annual rainfall of 1320 mm is recorded in this province. The mean minimum temperature in the dry cold month of June is 6.8°C and the mean maximum temperature in dry hot month of October is 30.6°C (3). The province is located within the Central African plateau.Mosquito samplingSampling was conducted in April-May 2013, in the transition from wet to the drier month (3).Larvae: Larval searches were conducted in rural, urban and peri-urban areas of the province. Both inside and outside house searches for larvae were made. The survey team covered at least 10 households per day. The term household meant one or more people who lived in the same dwelling and also shared meals or living accommodation.Indoor inspection included flower-pots and water storage, whereas outside inspection included wells, discarded Clay-pots, discarded bottles and plastic containers; banana (Musa sapientum) leaf axils, discarded tyres and edges of water canals. The collected mosquito larvae were kept in larval bottles (Figure 1). Mosquito larval data included province, district, locality (urban or rural), house number (randomly allocated during sampling) and date of collection.Adults: Adult mosquitoes were sampled by three research teams consisting of four persons per team. The following sampling methods were used to collect adult mosquitoes: backpack aspirators, aspiration using a mouth aspirator tube, CDC Light trap and the Gravid Light traps. Mosquito collections were made inside and outside households in different ecological locations: rural, urban, forest and plains. Outdoor mosquitoes were captured using backpack aspirator, CDC Light trap and the Gravid Light trap for collecting gravid (egg-laying) females to increase the chance for virus isolation. Sampling mosquitoes using back pack aspirator was conducted outdoor between 16.00 hours and 19.00 hours. Indoor adult resting mosquitoes were collected by various methods such as a mouth aspirator tube using a torch to locate these resting sites and knockdown spray catch with pyrethroid insecticide in randomly selected dwellings which commenced at 06.00 hours. All adult mosquitoes collected from the field were sorted and pooled by site of collection, sex and stored in liquid nitrogen to maintain mosquito morphological features.Mosquito larval rearingSampled mosquito larvae were transported to the Tropical Diseases Research Centre (TDRC) Insectary Laboratory in Ndola, Zambia, to rear them into the adult stage for species identification using entomological keys (5-7). At the TDRC Laboratory, the larvae were fed on fish flakes Tetramin and maintained at relative humidity of 80+2% and temperature 23+2°C. Emerged adult mosquitoes were stored at -80°C to preserve their viability.Shipment, viral tests and vector species identificationSixty adult Aedes species mosquitoes were airfreighted to Institute Pasteur in Dakar (IPD), Senegal to test for the presence of arthropod-borne viral activity in the Aedes specimen vector species by Reverse Transcriptase Polymerase Chain reaction (RT-PCR) technique and to identify and/or validate the sub-sample species. …