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United States Department of Agriculture

Agricultural Research Service

Research Project: Bionomics and Control of Rift Valley Fever Virus Vectors in Kenya

Location: Mosquito and Fly Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
1. Determine the animal and mosquito species that serve as the inter-epizootic maintenance hosts of Rift Valley fever virus (RVFV) virus. 2. Test candidate repellents for biting insects. 3. Test and evaluate efficacy of control treatments.


1b.Approach (from AD-416):
1. Determine mosquito blood meal sources for blood-fed females collected during an outbreak (previously collected) and during an inter-epidemic period. Test collected mosquitoes for the presence of RVFV using RT-PCR. Determine mosquito succession from the onset of rain events leading to flooding until flooded areas are dry. 2. Evaluate the efficacy of a candidate repellent for use on humans in terms of how well it protects against insect bites and how well it would be received and actually used in an emergency distribution situation. 3. Evaluate the efficacy of chemical mosquito control that is applied prior to rain events.


3.Progress Report:

This research relates to the inhouse project Objective 6: Discover and characterize environmental predictors of the distribution of mosquitoes in order to assess the risk of invasive species and pathogen transmission. Apply to the development of methods and techniques to accurately assess mosquito population density, to deploy vector surveillance systems, and to detect exotic invasive species.

Two genes (CO1and cytb genes) found in DNA taken from in the mosquito blood meals were amplified by PCR and sequences of purified amplicons queried in GenBank and Barcode of Life Database (BOLD) to identify blood meal sources. Seventy-three percent of the mosquitoes from Garissa were Aedes ochraceus and 23% Aedes mcintoshi, and both species preferentially fed on goats, cattle, sheep and humans. In Baringo, 38% of Mansonia uniformis had fed on sheep. Eight Rift Valley fever virus isolates were from Ae. ochraceus blood meals from human (1), cattle (1), sheep (4), goat (1) and unidentified host (1). Of these, mosquitoes with blood meals from sheep (3), goat (1) and unidentified host (1) had disseminated infection. The only RVFV positive Aedes mcintoshi (with disseminated infection) blood meal was from donkey. In Baringo all the 4 Mansonia uniformis that fed on sheep had disseminated infection. Ndumu virus (NDUV) was also isolated from blood meals of some mosquitoes in Garissa. Thirteen of the NDUV were from Ae. Ochraceus (7), Ae. mcintoshi (5) and Ae. sudanensis (1). No mixed infections in mosquitoes were detected although both viruses shared the same vectors. These data have shown that RVFV and NDUV were co-circulating during the outbreak. The observation that humans were hosts to RVFV vectors and were possibly involved in human-mosquito-human transmission of the virus is quite significant.


Last Modified: 12/18/2014
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