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United States Department of Agriculture

Agricultural Research Service

Research Project: BITING ARTHROPODS: INTEGRATED PEST MANAGEMENT

Location: Mosquito and Fly Research Unit

Title: Rift Valley fever virus-infected mosquito ova and associated pathology: possible implications for endemic maintenance

Authors
item Romoser, William -
item Oveido, Marco Neira -
item Lerdthusnee, Kriangkrai -
item Patrican, Lisa -
item Turell, Michael -
item Dohm, David -
item Linthicum, Kenneth
item Bailey, Charles -

Submitted to: Journal of Research and Reports in Tropical Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 15, 2011
Publication Date: September 16, 2011
Citation: Romoser, W.S., Oveido, M., Lerdthusnee, K., Patrican, L.A., Turell, M.J., Dohm, D.J., Linthicum, K., Bailey, C. 2011. Rift Valley fever virus-infected mosquito ova and associated pathology: possible implications for endemic maintenance. Journal of Research and Reports in Tropical Medicine. 2:121-127.

Interpretive Summary: Rift Valley fever virus is an important disease of livestock and people in Africa and the Middle East. The virus is thought to remain in nature by being passed from female Aedes micintoshi mosquitoes to her eggs and then on to subsequent generations. This study examined the ovaries of mosquitoes artificially infected with the virus. Virus was specifically stained with dye to determine the location of the virus in the ovaries. Various tissues in the ovaries were found to be infected, including the eggs. These findings support the hypothesis that Aedes mcintoshi is involved in the survival of Rift Valley fever in nature.

Technical Abstract: Background: Endemic/enzootic maintenance mechanisms like vertical transmission, pathogen passage from infected adults to their offspring, are central in the epidemiology of zoonotic pathogens. In Kenya, Rift Valley fever virus (RVFV) may be maintained by vertical transmission in ground-pool mosquitoes such as Aedes mcintoshi. RVFV can cause serious morbidity, and mortality in humans and livestock. Past epidemics/ epizootics were in sub-Saharan, but since the late 1970’s RVFV has also appeared in North Africa and the Middle East. Preliminary results revealed RVFV-infected eggs in Ae. mcintoshi following virus injection into the hemocoel after the first of two blood meals, justifying further study. Methods: Mosquitoes were collected from an artificially flooded water-catching depression along a stream in Kenya, shipped live to the U.S., and studied using an immunocytochemical method for RVFV antigen localization in mosquito sections. Results and Conclusions: Following virus injection into the hemocoel we found RVFV-infected reproductive tissues, particularly follicular epithelia and oocyte/nurse cells. Ovarian infection from the hemocoel is a crucial step in establishing a vertically transmitting mosquito line. Ovarian follicles originate from germarial cells, primordia located distally in each ovariole and infection of these cells is expected to be requisite for long-term vertical transmission. However, we found no germarial cell infection, so establishing a new line of vertically transmitting mosquitoes may require two generations. Our findings support the hypothesis that Ae. mcintoshi is involved in the endemic maintenance of RVFV by vertical transmission. Detection of distinct pathology in infected eggs raises the possibility of virus-laden eggs being deposited among healthy eggs, thereby providing an exogenous source of infection via ingestion by mosquito larvae and other organisms. This has potentially significant epidemiological implications. Possible modes of entry of virus from the hemocoel into the ovaries and routes by which larvae might become infected by ingesting virus are discussed.

Last Modified: 4/17/2014
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