The Pathogenesis and Pathology of Infection in Calves with a Strain of Bovine Adenovirus Type 3

Abstract

SUMMARY Eight colostrum-deprived calves were inoculated intranasally on the day of birth with 10 ml. of a strain (IVBR 1) of bovine adenovirus Type 3, and with a further 10 ml. of the same virus given intratracheally 24 hr. later. The inoculum had a mean infectivity titre of 104·0 TCID50 per ml. Three calves were killed at 4 days, 3 at 7 days and the remaining 2 calves at 3 months. A further 2 calves were inoculated in the same way with trypsin-treated WBR 1 virus and both were killed at 7 days. This inoculum had an infectivity titre comparable with that of the untreated virus. All calves showed a mild clinical reaction comprising some conjunctival and nasal discharge and a degree of pyrexia. Two calves exhibited respiratory embarrassment. In 6 calves, the onset of pyrexia was accompanied by a diarrhoea lasting 2 to 4 days. Swabs were made daily from conjunctiva, nose and rectum; virus was recovered from the faeces up to 10 days after infection and from the eye and nose up to 11 days. Virus was recovered from the nose of 1 calf after 3 weeks. No viraemia was demonstrated in any of the calves. At necropsy, gross lesions were confined principally to the lungs, which showed areas of collapse, consolidation and emphysema, and were especially marked in those calves inoculated with untreated virus and killed at 4 or 7 days. Lesions were discrete in the lungs of calves killed at 3 months and in those inoculated with trypsin-treated virus. Histological changes in the lungs of calves killed on the fourth and seventh days consisted of a proliferative bronchiolitis and necrosis with bronchiolar occlusion which resulted in alveolar collapse. Typical adenovirus intranuclear inclusions were observed in a variety of tissues including lung, tonsils, tracheal mucosa and in retropharyngeal, mediastinal and bronchial lymph nodes. Residual lesions consisting of scar tissue and some degree of lympho-reticular hyperplasia were seen in the lungs of calves killed 3 months after infection. Virus was recovered from the lung lobes of the calves inoculated with untreated virus and killed at 4 or 7 days, but not from those killed at 3 months or those infected with trypsin-treated virus. Precipitating antibody to the group reactive antigen of adenoviruses was demonstrated by immunodiffusion in the sera of calves 3 to 4 weeks following infection. Such antibody persisted until the animals were killed at 3 months. Two control calves inoculated with virus-free fluid and maintained in pens adjacent to the infected calves remained healthy, free of virus and showed no evidence of disease when killed at 4 and 7 days respectively. The role of adenoviruses in bovine respiratory disease and their possible implication in pneumo-entcritis of calves is discussed.