Mosquito-borne arbovirus surveillance at selected sites in diverse ecological zones of Kenya; 2007 – 2012

Abstract

BackgroundIncreased frequency of arbovirus outbreaks in East Africa necessitated the determination of distribution of risk by entomologic arbovirus surveillance. A systematic vector surveillance programme spanning 5 years and covering 11 sites representing seven of the eight provinces in Kenya and located in diverse ecological zones was carried out.MethodsMosquitoes were sampled bi-annually during the wet seasons and screened for arboviruses. Mosquitoes were identified to species, pooled by species, collection date and site and screened for arboviruses by isolation in cell culture and/or RT-PCR screening and sequencing.ResultsOver 450,000 mosquitoes in 15,890 pools were screened with 83 viruses being detected/isolated that include members of the alphavirus, flavivirus and orthobunyavirus genera many of which are known to be of significant public health importance in the East African region. These include West Nile, Ndumu, Sindbis, Bunyamwera, Pongola and Usutu viruses detected from diverse sites. Ngari virus, which was associated with hemorrhagic fever in northern Kenya in 1997/98 was isolated from a pool of Anopheles funestus sampled from Tana-delta and from Aedes mcintoshi from Garissa. Insect only flaviviruses previously undescribed in Kenya were also isolated in the coastal site of Rabai. A flavivirus most closely related to the Chaoyang virus, a new virus recently identified in China and two isolates closely related to Quang Binh virus previously unreported in Kenya were also detected.ConclusionActive transmission of arboviruses of public health significance continues in various parts of the country with possible undetermined human impact. Arbovirus activity was highest in the pastoralist dominated semi-arid to arid zones sites of the country where 49% of the viruses were isolated suggesting a role of animals as amplifiers and indicating the need for improved arbovirus disease diagnosis among pastoral communities.

Entomological Coinfections of Arboviruses Dengue and Chikungunya Viruses along the Coastline of Kenya

“…The rates of arboviral infection in the Aedes species did not vary significantly along the coastline. This might mean all serotypes of Dengue virus are in circulation (Ochieng et al, 2013) and human infection can occur in similar proportions.…”

“…DENV specific RNA was amplified in a total of 25 µl reaction mixture (12.5 μl of Amplitaq Gold 360 PCR master mix-Applied bio systems, USA, 50 picomoles each of forward and reverse primer, 2 μl of the cDNA and 9.5 μl of DEPC treated water to top up to 25 μl). The list of primers used (Table 1) were adapted from (Konongoi et al, 2016); (Normile, 2013) and (Ochieng et al, 2013). The PCR plates were placed in the real time thermo cycler and were cycled at 50°C for 20 minutes, 95°C for 5 minutes, followed by 40 cycles of 95°C for 15 seconds, 60°C for 30 seconds, and 70°C for 1 minute, and a final extension for 10 minute at 72°C.…”

“…The PCR program consisted of an initial denaturation at 95°C for 2 min and 40 cycles of 30 seconds denaturation at 95°C, 30 seconds annealing at 55°C, 1 minute elongation at 72°C and final extension at 72°C for 5 minutes. Presence of flaviviruses was screened in all the amplified products using the pan-flavivirus primer (Ochieng et al, 2013) in Table 2. Samples testing positive with flavivirus family primers were further tested with the conventional primers for Chikungunya virus (Redd et al, 2012).…”

“…These viruses are maintained in the zoonotic cycle with humans as incidental dead-end host with limited role in the maintenance of this cycle (Ochieng et al, 2013). In the ecosystem, the viruses are incubated through intrinsic and extrinsic incubation.…”

Usutu virus: current knowledge and future perspectives

“…47 Later on, the virus has been isolated from several mosquito species throughout the African continent, mainly in countries where surveillance programs are implemented, such as Senegal, CAR, Burkina Faso, Cote d´Ivorie, Nigeria, and Uganda, 48 and more recently in Kenya. 49 Experimental oral infection of C. neavei has been demonstrated and, although virus transmission to bitten mice was not initially observed, USUV infection, dissemination, and transmission rates were later on reported, showing the importance of high virus titers in the blood meal for virus infection. 50 In addition to C. neavei, USUV has been also isolated from other Culex species, including Culex quinquefasciatus, an anthropophilic vector that was directly implicated in the emergence of the virus in Europe, 48 and from Aedes mosquitoes.…”