Neutralizing antibody to bovine adenovirus serotype 3 in healthy cattle and cattle with respiratory tract disease.

: A serosurvey of healthy cattle for the presence of serum-neutralizing antibody to bovine adenovirus serotype 3 (BAV-3) established the widespread prevalence of this agent in Iowa cattle. Of the animals studied, 19.1% (involving 157 calves that represented 40 outbreaks (herds) of respiratory tract disease) seroconverted to BAV-3. This pathogen was implicated serologically as being involved in the cause of respiratory tract disease in six herds. Bovine adenovirus serotype 3 was isolated from cattle in two of these herds. Based on seroconversion and lack of isolation of other viral agents, it appeared that BAV-3 could have been the sole virus involved in the respiratory tract disease in one of these two herds. In another herd, seroconversion was observed only to BAV-3, but other viral agents as well as BAV-3 were isolated. The remaining four herds presented a problem because the cattle seroconverted to more than one agent and additional viral agents were isolated from some animals. Whether the disease manifestations observed in these six herds were due solely or in part to BAV-3 can only be speculated. Cattle are capable of undergoing a natural infection, as indicated by seroconversion, in the absence of overt clinical signs of illness. It appears that maternal (passive) antibody decreases to a point at which infection by this virus becomes possible and an active immune response occurs.