Location: Foreign Animal Disease Research2011 Annual Report
1a. Objectives (from AD-416)
1: Assess the role of insect vector transmission on the pathogenesis of VSV and generate scientific information to understand the epidemiology and trade significance of VSV infection.
1b. Approach (from AD-416)
The assessment of the role of insect vector transmission will be accomplished by; a.) Examining the transmission of Vesicular Stomatitis Virus New Jersey (VSVNJ) to cattle by infected S. vittatum (black fly) bite. b.) Examining the effect of salivary gland extracts on VSV infection in cattle. c.) Evaluating cattle as amplifying hosts for VSV transmission by black flies.
3. Progress Report
During FY 2011 we were able to establish a system to measure the effect of black fly salivary gland extracts (SGE) on bovine primary cells. We confirmed for the first time that SGE decrease the expression of type I IFN activity. This is relevant as it provides a likely mechanism to explain previous observations in-vivo where animals inoculated with VSV by allowing bites from infected insects developed more severe disease with less virus than animals inoculated through needle scarification of the skin. We also continued work started in 2010, analyzing samples and data from cattle experiments carried out both at PIADC and at the University of Georgia. We confirmed our previous finding that, despite the absence of viremia, cattle can serve as amplifying hosts in at least two ways by serving as a source of virus to insects feeding at or near lesions and in as an unconventional amplifying host by horizontal transmission among flies while co-feeding on the same cattle host, regardless of the disease status of the animals. This information is pivotal in implementing effective control programs for the control of VSV incursions in the US. Additionally, continued a collaborative study in endemic areas of Mexico showing that seroconversion of cattle occurs during periods of high insect activity and that specific viral lineages dominate the transmission of VSV in northern Mexico and likely serve as the source of outbreaks in the US. Our findings continue to provide valuable information for disease ecology and modeling of the disease and its control methods. The research conducted in FY 2011 addresses objective 1). “Assess the role of insect vector transmission on the pathogenesis of VSV and generate scientific information to understand the epidemiology and trade significance of VSV infection” of this project. This research addresses the biodefense research of foreign animal diseases objective 1) “development and/or improvement of surveillance tools”.
1. Determined mechanism for increased insect transmission of vesicular stomatitis virus infection. Vesicular stomatitis (VS), a disease that resembles foot-and-mouth disease (FMD), occurs sporadically in the US causing economic losses. Unlike FMD, VS is insect transmitted but the mechanisms of transmission and disease spread are poorly understood. ARS researchers at PIADC, Greenport, NY, in collaboration with scientists at the University of Georgia-Athens have previously shown that insect transmission to cattle results in more severe disease than needle inoculation. They have now shown that factors in the insect saliva decrease the ability of cattle to respond to viral infection and that is why transmission is increased. This information is relevant to USDA-APHIS veterinary services by focusing control of VSV outbreaks in limiting animal exposure to biting insects. This information is also useful in understanding the effect of insect bites on the immune system of livestock species.
Adell, A.D., Perez, A.M., Navarro, R., Lopez, I., Paz, P., Rodriguez, L.L. 2010. Estimation of the time of seroconversion to the New Jersey serotype of vesicular stomatitis virus in sentinel cattle of dairy herds located at high and low elevations in southern Mexico. American Journal of Veterinary Research. 71(12):1451-1456.