2013 Annual Report
1a.Objectives (from AD-416):
To characterize the susceptibility, pathogenesis, and virus-vector-host interactions in bluetongue virus (BTV) and vesicular stomatitis virus (VSV) animal infections.
1b.Approach (from AD-416):
Animal infection studies will be conducted with vesicular stomatitis virus (VSV)and exotic bluetongue virus (BTV). The role of Culicoides sonorensis midge saliva in the ability of vesicular stomatitis virus to establish infection, replicate, and persist, will be examined using feral pigs. The physiological variations in VSV infected bats and guinea pigs and their affect on vector-host selection will be determined. The susceptibility of U.S. sheep and white-tailed deer to infection by exotic BTV serotype 8 will be determined. Bite rates, viral transmission, infection rates and pathogenesis will be measured by methods to include: clinical disease observations, virus isolation/plaque assay, polymerase chain reaction, ELISA, ethogram cataloging, videography, necropsy, histopathology, and immunohistochemistry. For all studies, scientists with complementary expertise from both parties will work together to obtain, analyze, and interpret the research data.
The major accomplishment of this agreement was the completion of processing and testing all samples from the BTV-8 North American sheep susceptibility study in the BSL-3Ag Biosecurity Research Institute facility. To summarize, eight sheep yearlings were inoculated with bluetongue serotype 8 (BTV-8) obtained from the Central Veterinary Institute of Wageningen, The Netherlands. Temperatures and clinical signs were monitored daily during the peak of disease and then periodically thereafter for 28 days. Blood was collected at varying intervals throughout the study and tested by real time polymerase chain reaction for BTV RNA (developed by ABADRU), and for BTV specific antibody by competitive ELISA (developed by ABADRU). Virus isolation and PCR analyses were performed on day 8 (peak disease) tissue samples from two sheep. Additionally, histopathological examinations were performed on Kidney, liver, spleen, adrenal gland, heart, lung, intestine, lymph node tissues. Highest blood virus titers were detected between 7 and 14 days post inoculation. Virus distribution in tissues was widespread with the highest titers found in the spleen and draining lymph nodes of the head and neck.
The disease level seen was similar to our domestic BTV virus types and less severe than what has been reported for European sheep species with this specific virus type. Our results indicate that if BTV-8 were to be introduced into the U.S., our sheep populations would be highly susceptible to infection, but clinical disease would not be more severe than outbreaks resulting from many of our domestic BTV types.