SYSTEMIC VACCINATION WITH INACTIVATED BOVINE VIRUS DIARRHEA VIRUS PROTECTS AGAINST RESPIRATORY CHALLENGE

Inactivated bovine virus diarrhoea virus, strain 11249nc, inoculated s ubcutaneously three times with Quil-A into calves protected against in tranasal challenge with the same strain. Virus was isolated from nasop haryngeal swabs taken 4 to 8 days post challenge and blood taken 4 to 6 days post challenge from control calves but not from vaccinated calv es. A second strain of virus, Ky1203nc, was selected on the basis of p reviously established data on its antigenicity and the amount of viral antigen produced by five cell cultures compared using an ELISA. Cultu res of one cell line, MDBK, yielded a greater amount of viral antigen than the others. Strain Ky1203nc grown in MDBK cells was inactivated w ith beta-propiolactone, mixed with adjuvant and used as a vaccine inoc ulated into calves subcutaneously three times. All of 5 calves were pr otected against intranasal challenge with a heterologous strain. In co ntrast virus was isolated from nasopharyngeal swabs taken from 5 contr ol calves and from the blood of 4 controls. All 5 control calves, but none of the vaccinates, had a leukopenia after challenge. We conclude that the selected strain and system of vaccine preparation provide an effective means of protecting calves against respiratory infection and that live vaccines are not required to protect against challenge via the respiratory tract.