2009 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.
In FY 2009 we continued research on the pathogenesis of vesicular stomatitis virus in cattle, particularly focusing on insect-transmitted infection, early events in viral infection and host responses. Due to the small size of this project, most of the research activities are done through two collaborative agreements with colleagues at the University of Georgia-Athens (UGA).
A cattle infection model utilizing infected black flies developed under this project was used to study pathogenesis, host responses and the ability of cattle to serve as amplifying host to VSV infection. Coronary band inoculation in cattle using infected fly bite resulted in clinical disease with 1,000 – 10,000 lower viral dose those than that needed when direct inoculation by scarification was used. Fly bite inoculation resulted in presence of viral RNA in the draining lymph node earlier and in greater amounts than direct scarification. Using negative sense riboprobe in situ hybridization, this detected RNA is positive sense, indicating that the virus is undergoing replication in the draining lymph node at this early time after infection. Results indicate that fly bites possess factor for potentiating viral infection, enabling VSV to infect and cause disease with a much lower dose of virus. In addition research was conducted at UGA to complete the studies initiated at PIADC in 2008. Specifically the ability of VSV infected cattle to serve as source of virus to uninfected black flies feeding in their lesions was demonstrated. These experiments complement research demonstrating that black flies can be a source of infection to cattle and cattle can serve as amplifying hosts for VSV infection. Manuscripts describing these results are under preparation.
Demonstrated that cattle can serve as amplifying hosts for Vesicular Stomatitis Virus New Jersey Virus (VSNJV). In this series of studies we demonstrated transmission from VSNJV-infected black flies to naive black flies while co-feeding on non-infected cattle. We also showed that black flies can infect cattle resulting in clinical disease and that naïve black flies feeding in cattle lesions can become infected. Together these findings demonstrate that cattle can be amplifying hosts during VSV epidemics. These findings are significant since the little is known regarding VSNJV transmission and infection (pathogenesis) in cattle. Our results represent the first report of clinical VS occurring in cattle following the bite of a VSNJV-infected black fly.
Described the early stages of Vesicular Stomatitis Virus (VSV) infection cattle after infection by fly bite or scarification. The viral replication kinetics in vivo and the influence of fly bite in lesion development after VSV infection were described. Studies involving the early phages of VSV infection had not been previously described comparing fly bite and scarification inoculation methods. At 12 HPI lesions were present only in small focal areas of the CB epidermis whereas at 24 HPI, there was widespread and coalescing intra- and inter-epithelial edema predominantly in the midzone of the stratum spinosum. From 72 to 120 HPI there was extensive epithelial necrosis with cleft formation and loss of the epidermis. In situ hybridization revealed intense cytoplasmic signal in keratinocytes from 12 until 48 HPI in both FB and SC groups, with faint staining at 72 and 96 and no staining at 120 HPI. In the lymph nodes, ISH highlighted scattered cells at cortical and subcapsular areas at 24 HPI only. Immunohistochemistry in coronary band showed intense cytoplasmic labeling of keratinocytes until 72 HPI, with faint staining at 96 and 120 HPI. In the lymph nodes, in contrast to what was observed with ISH, there was positivity until 120 HPI, with positive cells stained in the subcapsular regions at 24 HPI and at perifollicular regions after 48 HPI. Positive VI and rRT-PCR were restricted to the site of inoculation and draining LNs. Inoculation by scarification or fly bite resulted in very similar disease, despite the fact that flies inoculum was 3-4 log10 lower than scarification dose. These results suggest that there may be factors facilitating infection induced by the fly bite.
Reis, J.L., Mead, D., Rodriguez, L.L., Brown, C.C. 2009. Transmission and pathogenesis of vesicular stomatitis viruses. Brazilian Journal of Veterinary Pathology. 2(1):49-57.
Mead, D.G., Lovett, K.R., Murphy, M.D., Pauszek, S.J., Smoliga, G.R., Gray, E.W., Noblet, R., Overmyer, J., Rodriguez, L.L. 2009. Experimental Transmission of Vesicular Stomatitis New Jersey Virus From Black Flies (Simulium vittatum) To Cattle: Clinical Outcome Is Determined By Site of Insect Feeding. Journal of Medical Entomology. 46(4):866-872.