2011 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 the susceptibility of white-tailed deer study. Eight white-tailed deer yearlings were inoculated with bluetongue serotype 8 (BTV-8) obtained from the Central Veterinary Institute of Wageningen, The Netherlands. Two deer were sham inoculated and housed with the infected deer to verify no direct contact transmission with this isolate. 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). All eight deer became clinically ill. On day 8 at the peak of disease tissues from two deer were examined for virus distribution. Gross necropsy findings and histopathological findings showed severe interstitial pneumonia in these two deer, a common secondary infection in bluetongue outbreaks. Kidney, liver, spleen, adrenal gland, heart, lung, intestine, mandibular lymph node, and mesenteric lymph node tissues were taken at necropsy and formalin fixed for histopathology and frozen for RNA extraction and real time PCR analysis.
Peak viremias, as detected by real time PCR, were from 8-12 days post inoculation (dpi). Peak antibody titers, as detected by cELISA, were from 12-21 dpi and persisted throughout the experiment. Virus was detected by real time PCR in all tissues of all but two deer indicating a widely disseminated infection.
The disease level seen in North American deer was more severe than what has been reported for European deer species with this serotype, both naturally and experimentally infected. However, levels were similar to what we have seen in some outbreaks of our domestic serotypes. Thus, these results do not suggest that this isolate has an increased virulence for our white-tailed deer population as compared to our domestic serotypes. These results suggest that if BTV-8 were to be introduced into the U.S., we would expect our white-tailed deer populations to be highly susceptible to infection. In that bluetongue outbreaks typically last 1-2 months and the majority of surviving deer were still viremia at 28 days suggests they would provide significant virus amplifying reservoirs for subsequent transmission of virus by Culicoides to livestock.
This research supports NP103 Action Plan Components 1. Biodefense Research and 3. Prevent and Control Zoonotic Diseases.
ADODR is directly involved in performance of the research and also monitors activities to evaluate research progress through site visits, meeting at conferences, email and phone calls.