The pathogenesis of epizootic hemorrhagic disease of deer (EHD) was studied in suckling white mice and white-tailed deer (Odocoileus virginianus) using these approaches: (1) measurement of hematological values, (2) assay of virus in various organs, and (3) detection of viral antigen within tissues using the direct fluorescent antibody technique. An increase in bleeding time was the only hematological change observed in mice. The virus content of the brains of infected mice increased rapidly during the early days of infection but little virus was found in other organs. Fluorescing viral antigen was detected only in the brains of acutely ill mice.

Infected deer had an increase in total erythrocyte counts as well as corresponding changes in erythrocyte-associated values. Although the percentage of neutrophils in the blood increased during infection, total leukocyte counts remained unchanged. Virus was isolated during the clinical illness from 13 of 16 organs tested. No viral antigen was demonstrated in any tissue by the direct fluorescent antibody technique.