Evaluation of white-tailed deer host resistance factors to epizootic hemorrhagic disease viruses

Epizootic hemorrhagic disease (EHD), caused by viruses (EHD virus serotypes 1 and 2) in the epizootic hemorrhagic disease virus serogroup (Reoviridae: Orbivirus), is one of the most important infectious diseases of white-tailed deer (Odocoileus virginianus). Great variation in the frequency and severity of EHD epizootics in North America have been observed. Variation in clinical response also has been reported in white-tailed deer experimentally infected with EHD viruses. Potentially important host-related resistance factors affecting severity of this disease in white-tailed deer include innate host resistance, protection by maternal antibodies, and antibody-conferred immunity. Experimental studies were performed to determine if these host-related factors can contribute to the variation seen in the frequency and severity of EHD epizootics or in the severity of disease in individual deer infected with EHD viruses.; At an enzootic site studied in Texas, 100% of fawns had maternal antibodies to EHD and BT viruses and were naturally exposed to EHD and/or BT viruses while maternal antibodies were present. Maternal antibodies may have contributed to the lack of clinical disease seen during natural exposure, but did not prevent infection nor viremia.; Results of experimental infections of deer with both EHD virus serotypes 1 and 2 suggest that innate resistance to EHD does occur in deer from Texas and possibly parts of North Carolina. Should innate resistance extend to deer from other southern latitudes it may explain why severe clinical disease and mortality are seen in EHD in northern latitudes, while epizootics in southern latitudes often result in mild or inapparent disease.; Experimental infection of deer with EHDV-2 lessened clinical disease severity in fawns subsequently challenged with EHDV-1, but did not reduce EHDV-1 viremia. Field data suggests that reciprocal cross protection also occurs. Although cross-protection occurs between these two viruses, it does not prohibit deer from acting as virus amplifying hosts.; Maternal antibodies, innate resistance, and cross-protection between EHD viruses all may contribute to white-tailed deer host-resistance and explain much of the observed temporal and spatial variation previously reported from the filed.