PATHOGENESIS AND CLINICAL SIGNS OF EQUINE HERPESVIRUS-1 IN EXPERIMENTALLY INFECTED PONIES IN-VIVO

Equine herpesvirus-l (EHV-1) causes respiratory disease, neonatal deat h, abortion and neurologic disease. The main purpose of this study was to identify viral antigen in respiratory tract samples by immunoperox idase staining. Six pony foals were selected on the basis of demonstra ting seronegativity to EHV-1 by virus neutralization and housed in iso lation. They were infected experimentally by administering EHV-1 nebul ized ultrasonically through a face mask. Successful infection was clin ically apparent as each of the foals had febrile responses, nasal disc harge, and enlarged submandibular lymph nodes. Sporadic coughing was a lso heard. EHV-1 was isolated from nasopharyngeal swabs of 4/6 ponies and seroconversion was demonstrated in all foals. Bronchoscopic examin ation of the large airways revealed hyperemia. The incidence of recove ry of Actinobacillus suis from nasopharyngeal swabs increased initiall y, with recovery of Streptococcus zooepidemicus isolates predominating at 3 wk post-infection. Cytology brushes were used to sequentially sa mple the respiratory tract of the infected ponies at the nasopharynx, mid-trachea and the mainstem bronchus. Bronchoalveolar lavage provided lung cells. Immunocytochemistry techniques were applied to both types of samples to locate EHV-1 antigen. Indirect immunoperoxidase stainin g of samples utilizing monoclonal antibodies specific for EHV-1 demons trated viral antigen associated with cellular debris, primarily in the nasopharyngeal samples on days 3-9 post-infection.