Pathological changes associated with equine arteritis virus infection of the reproductive tract in prepubertal and peripubertal colts.

The nature and extent of changes associated with equine arteritis virus (EAV) infection of the reproductive tract was documented in 21 prepubertal and 15 peripubertal colts. This study was part of an investigation into the relationship between stage of reproductive tract maturity and susceptibility to the experimental establishment of persistent infection with EAV. After intranasal challenge with a field isolate of EAV, all colts developed clinical signs of equine viral arteritis (EVA) from which they recovered rapidly. Clinical signs during the acute phase consisted of fever, serous to mucopurulent ocular and nasal discharge, oedema of the limbs, scrotum or prepuce, scleral injection, conjunctivitis, icterus, cough, diarrhoea, stiff gait, lethargy, inappetence and depression. At necropsy, the most significant macroscopic lesions included excessive accumulation of fluid within the thoracic and abdominal cavities, lymph node enlargement and oedema of the reproductive tract. Colts killed 7 to 14 days after challenge had acute necrotizing vasculitis involving the testes, epididymides, vasa deferentia, ampullae, prostatic lobes, vesicular glands and bulbourethral glands. Vasculitis was characterized by striking fibrinoid necrosis of small muscular arteries with extravasation of erythrocytes and proteinaceous material into the media, adventitia and perivascular tissues. Colts examined on days 28-180 had lymphocytic and plasmacytic inflammatory cell infiltrates in the lamina propria and muscularis of the epididymides and accessory sex glands. The vascular lesions found during the acute phase of EAV infection contrasted with the multifocal lympho-plasmacytic infiltrates found within the parenchyma of the reproductive tract during the chronic phase. One peripubertal colt was found to be persistently infected with EAV 15 months after challenge. This colt had marked lympho-plasmacytic infiltrates in the ampullae at necropsy.