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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.
Highlights
Increased frequency of arbovirus outbreaks in East Africa necessitated the determination of distribution of risk by entomologic arbovirus surveillance
Mosquito collection and pooling A total of 450,680 mosquitoes were collected mostly by CDC Light trapping. 15,890 mosquito pools each containing up to 25 mosquitoes, were tested by cell culture screening and 158 pools of Aedes aegypti screened by RT-PCR
In West Africa, Ngari virus has been isolated from diverse mosquito species including Anopheles and Culex [21]. These findings demonstrate the risk of Ngari virus and other arboviruses causing outbreaks/infections in multiple locations/populations in Kenya, findings that must be brought to the attention of public health authorities to encourage and improve disease detected and prevention
Summary
Increased frequency of arbovirus outbreaks in East Africa necessitated the determination of distribution of risk by entomologic arbovirus surveillance. Most of these viruses are maintained in zoonotic cycles and humans are usually incidental dead-end host with an insignificant role in maintaining the cycle of the virus [2] They cause clinical syndromes of varying severity in humans and animals, ranging from self-limiting febrile illnesses to life-threatening encephalitis and/or hemorrhagic fever in humans and overt to severe/fatal disease in animals [2]. Mosquitoes were collected and analyzed for arboviruses in eleven selected areas in Kenya as a means of assessing arbovirus distribution, the risk of human exposure to arbovirus disease and the potential for disease outbreaks and incriminating associated vectors for targeted control. This paper reports the arboviruses that were isolated and their associated vectors during the period 2007 to 2012
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