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.
The diversity of mosquito arbovirus vectors was investigated to define regional risk of arbovirus transmission in Kenya. Mosquitoes were sampled between April, 2007 and December, 2010 at thirteen sites across seven administrative provinces and ecological zones. CDC light traps were used to collect mosquitoes while human-landing collection was conducted in five of the sites to target dayfeeding Aedes (Stegomyia) species. Over 524,000 mosquitoes were collected and identified into 101 species, 30 of them known vectors of arboviruses endemic to Kenya. Ae. (Neomelaniconion)
Biodiversity and relative abundance of ticks and associated arboviruses in Garissa (northeastern) and Isiolo (eastern) provinces of Kenya were evaluated. Ticks were collected from livestock, identified to species, pooled, and processed for virus isolation. In Garissa, Rhipicephalus pulchellus Gerstacker (57.8%) and Hyalomma truncatum Koch (27.8%) were the most abundant species sampled, whereas R. pulchellus (80.4%) and Amblyomma gemma Donitz (9.6%) were the most abundant in Isiolo. Forty-four virus isolates, comprising Dugbe virus (DUGV; n = 22) and Kupe virus (n = 10; Bunyaviridae: Nirovirus), Dhori virus (DHOV; n = 10; Orthomyxoviridae: Thogotovirus),and Ngari virus (NRIV; n = 2; Bunyaviridae: Orthobunyavirus), were recovered mostly from R. pulchellus sampled in Isiolo. DUGV was mostly recovered from R. pulchellus from sheep and cattle, and DHOV from R. pulchellus from sheep. All Kupe virus isolates were from Isiolo ticks, including R. pulchellus from all the livestock, A. gemma and Amblyomma variegatum F. from cattle, and H. truncatum from goat. NRIV was obtained from R. pulchellus and A. gemma sampled from cattle in Isiolo and Garissa, respectively, while all DHOV and most DUGV (n = 12) were from R. pulchellus sampled from cattle in Garissa. DUGV was also recovered from H. truncatum and Amblyomma hebraeum Koch from cattle and from Rhipicephalus annulatus Say from camel. This surveillance study has demonstrated the circulation of select tick-borne viruses in parts of eastern and northeastern provinces of Kenya, some of which are of public health importance. The isolation of NRIV from ticks is particularly significant because it is usually known to be a mosquito-borne virus affecting humans.
All traditional surveillance techniques for Aedes aegypti have been developed for the cosmopolitan domestic subspecies Ae. aegypti aegypti, and not the sylvatic subspecies, Ae. aegypti formosus. The predominant form in Western Kenya is Ae. aegypti formosus that is rarely associated with human habitations but is linked to transmission of sylvatic dengue virus strains. We compared five surveillance methods for their effectiveness in sampling Ae. aegypti formosus with the goal of determining a sustainable surveillance strategy in Kenya. The methods included larval and pupal surveys, oviposition trapping, BG-Sentinel trapping, resting boxes, and backpack aspirations. Larval and pupal surveys collected the highest number of Ae. aegypti formosus (51.3%), followed by oviposition traps (45.7%), BG-Sentinel traps (3.0%), and zero collected with either backpack aspiration or resting box collections. No Ae. aegypti formosus larvae or pupae were found indoors. The results indicate that oviposition traps and outdoor larval and pupal surveys were better surveillance methods for Ae. aegypti formosus in Western Kenya. Journal of Vector Ecology 40 (2): 301-307. 2015.
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