Arbovirus Prevalence in Mosquitoes, Kenya | CDC EID

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Volume 17, Number 2–February 2011
Research
Arbovirus Prevalence in Mosquitoes, Kenya
A. Desiree LaBeaud,1 Laura J. Sutherland,1 Samuel Muiruri, Eric M. Muchiri, Laurie R. Gray, Peter A. Zimmerman, Amy G. Hise, and Charles H. King

Author affiliations: Children's Hospital Oakland Research Institute, Oakland, California, USA (A.D. LaBeaud); Case Western Reserve University, Cleveland, Ohio, USA (A.D. LaBeaud, L.J. Sutherland, L.R. Gray, P.A. Zimmerman, A.G. Hise, C.H. King); and Ministry of Public Health and Sanitation, Nairobi, Kenya (S. Muiruri, E.M. Muchiri)

Suggested citation for this article

Abstract
Few studies have investigated the many mosquito species that harbor arboviruses in Kenya. During the 2006–2007 Rift Valley fever outbreak in North Eastern Province, Kenya, exophilic mosquitoes were collected from homesteads within 2 affected areas: Gumarey (rural) and Sogan-Godud (urban). Mosquitoes (n = 920) were pooled by trap location and tested for Rift Valley fever virus and West Nile virus. The most common mosquitoes trapped belonged to the genus Culex (75%). Of 105 mosquito pools tested, 22% were positive for Rift Valley fever virus, 18% were positive for West Nile virus, and 3% were positive for both. Estimated mosquito minimum infection rates did not differ between locations. Our data demonstrate the local abundance of mosquitoes that could propagate arboviral infections in Kenya and the high prevalence of vector arbovirus positivity during a Rift Valley fever outbreak.

Emerging zoonotic diseases threaten the health and security of human and animal populations throughout the world (1). Because arthropod-borne viruses, or arboviruses, can be spread by competent mosquito vectors across great distances, they pose substantial risk to other regions in which the disease is currently nonendemic (1). Zoonotic arboviruses circulate in sylvatic and peridomestic cycles involving wild animals and nearby humans. Often these arboviruses remain undetected by health care systems (2–4). Kenya has had multiple arbovirus outbreaks in the past 2 decades resulting in economic and public health distress, including yellow fever in 1992 (5,6) and 1995 (7), chikungunya fever in 2004 (8), and Rift Valley fever (RVF) in 1997 (9) and 2006 (10). Much remains unknown about the true prevalence of arboviruses in Kenya and the mosquito vectors responsible for virus maintenance and transmission. We investigated the local abundance of mosquitoes in Kenya that are infected with RVF virus (RVFV) and West Nile virus (WNV); mosquitoes were collected near human habitation during a period of prolonged heavy rainfall.

Rift Valley fever virus, family Bunyaviridae, genus Phlebovirus, is a vector-borne virus endemic to Africa and the Middle East (11). Recent outbreaks of RVF have resulted in substantial human illness and livestock losses in Kenya (9,10,12). Domestic ungulates are a principal source of transmissible RVFV, and human infection has been associated with direct animal contact, specifically with cattle, sheep, and goats (2,9,12). It is unclear which, if any, animal species maintain RVFV during interepidemic periods, and it is possible that RVFV is maintained solely within arthropod vectors during these periods (13).

West Nile virus, family Flaviviridae, genus Flavivirus, is a vector-borne virus that is maintained in nature between mosquitoes and birds (11). Humans and other mammals are incidental hosts and do not play a role in the natural preservation of WNV (11). Because most WNV infections are self-limiting and subclinical, human infections in Kenya are often misdiagnosed (14). As a result, the true prevalence of WNV in the country is probably underestimated (15). Further clarification of the true presence and circulation of WNV in mosquito vectors could enhance human WNV case detection in the region.

Few studies have investigated the many mosquito species that harbor arboviruses in Kenya (16–21). Entomologic surveys have demonstrated that mosquitoes that usually facilitate outbreaks of arboviral diseases, specifically Aedes spp., Anopheles spp., and Culex spp., flourish in Kenya (16,18,19,22–26). At least 40 different mosquito species can harbor RVFV, although their ability to transmit RVFV varies (14,20,21,27–29). Furthermore, although many species are susceptible to RVFV infection, studies of mosquito vectors in northeastern Kenya have shown that the proportion of positivity in individual species differs greatly (5.9% An. squamosus, 30% Ae. ochraceus, 42% Ae. mcintoshi) (R. Sang, pers. comm.). RVFV can also be transovarially transmitted in at least 1 mosquito species, Ae. mcintoshi (17). The isolation of WNV from a non–blood-feeding male Cx. univattatus mosquito trapped in northwestern Kenya indicates that WNV also transmits transovarially in that region (23).

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Arbovirus Prevalence in Mosquitoes, Kenya | CDC EID


Suggested Citation for this Article
Suggested citation for this article: LaBeaud AD, Sutherland LJ, Muiruri S, Muchiri EM, Gray LR, Zimmerman PA. Arbovirus prevalence in mosquitoes, Kenya. Emerg Infect Dis [serial on the Internet]. 2011 Feb [date cited]. http://www.cdc.gov/EID/content/17/2/233.htm
DOI: 10.3201/eid1702.091666



1These authors contributed equally to this article.


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A. Desiree LaBeaud, Children's Hospital Oakland Research Institute, 5700 Martin Luther King Jr. Way, Oakland, CA 94609, USA; email: alabeaud@chori.org