Infectious bovine rhinotracheitis virus: studies on the venereal carrier status in range cattle.

Genital samples collected at autopsy from 193 beef cows representing 22 different herds in Northern Australia yielded only one isolate of infectious bovine rhinotracheitis (IBR) virus. Serological evidence showed 59 per cent of similar cows had prior infection with this virus and of 19 sero-positive cows tested, 11 (58-2 per cent) shed detectable IBR virus from the vagina after treatment with corticosteroids. Transitory lesions of the vagina and vulva developed in five of the treated cows. Twenty-six (65 per cent) of 40 sero-positive bulls shed detectable IBR virus into the prepuce after corticosteroid treatment. Except for one bull, virus was not isolated after corticosteroid treatment of sero-negative animals. IBR virus and mucosal disease (MD) virus were not isolated from nasal swabs before or after corticosteroid administration. No correlation was observed between initial circulating antiboyd titre and virus excretion after treatment. There were no significant changes in levels of serum antibody during the virus excretion period.