Pathologic features of horses given avirulent equine arteritis virus intramuscularly

Twenty horses that were seronegative for equine arteritis virus antibodies were inoculated IM with live equine arteritis virus vaccine. The inoculation did not cause clinical signs of disease. A mild, transient febrile reaction developed in 6 horses, 3 of which were in poor condition before inoculation. Six horses, 2 of which were in poor condition before inoculation, experienced mild lymphopenia. Necropsy revealed mild lesions in the lymph nodes of 6 horses (3 of which were in poor condition before inoculation). Maximum concentrations of virus were detected in the lymph nodes and were consistently present from postvaccination day 3 through 8. Lesser concentrations of virus were detected in the spleen of 5 horses, liver and kidney of 4, abdominal fluid of 3, pleural fluid of 2, and lungs and urine of 1, between postvaccination days 3 and 7. Virus was not detected in the brain, nasal tract, or serum of any of the horses.