Identification of a mutant bovine herpesvirus-1 (BHV-1) in post-arrival outbreaks of IBR in feedlot calves and protection with conventional vaccination.
Outbreaks of infectious bovine rhinotracheitis (IBR) have recently been observed in vaccinated feedlot calves in Alberta a few months post-arrival. To investigate the cause of these outbreaks, lung and tracheal tissues were collected from calves that died of IBR during a post-arrival outbreak of disease. Bovine herpesvirus-1 (BHV-1), the causative agent of IBR, was isolated from 6 out of 15 tissues. Of these 6 isolates, 5 failed to react with a monoclonal antibody specific for one of the epitopes on glycoprotein D, one of the most important antigens of BHV-1. The ability of one of these mutant BHV-1 isolates to cause disease in calves vaccinated with a modified-live IBR vaccine was assessed in an experimental challenge study. After one vaccination, the majority of the calves developed humoral and cellular immune responses. Secondary vaccination resulted in a substantially enhanced level of immunity in all animals. Three months after the second vaccination, calves were either challenged with one of the mutant isolates or with a conventional challenge strain of BHV-1. Regardless of the type of virus used for challenge, vaccinated calves experienced significantly (P < 0.05) less weight loss and temperature rises, had lower nasal scores, and shed less virus than non-vaccinated animals. The only statistically significant (P < 0.05) difference between the 2 challenge viruses was the amount of virus shed, which was higher in non-vaccinated calves challenged with the mutant virus than in those challenged with the conventional virus. These data show that calves vaccinated with a modified-live IBR vaccine are protected from challenge with either the mutant or the conventional virus.
van Drunen Littel-van den Hurk
S
S
Veterinary Infectious Disease Organization, University of Saskatchewan, Saskatoon, Canada. vandenhurk@sask.usask.ca
Myers
D
D
Doig
P A
PA
Karvonen
B
B
Habermehl
M
M
Babiuk
L A
LA
Jelinski
M
M
Van Donkersgoed
J
J
Schlesinger
K
K
Rinehart
C
C
D000416:Alberta / Q000453:epidemiology; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002417:Cattle; D004196:Disease Outbreaks / Q000517:prevention & control / Q000662:veterinary*; D007242:Herpesvirus 1, Bovine / Q000145:classification / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D007111:Immunity, Cellular; D007117:Immunization, Secondary / Q000662:veterinary; D007241:Infectious Bovine Rhinotracheitis / Q000453:epidemiology / Q000517:prevention & control / Q000821:virology*; D009154:Mutation; D011897:Random Allocation; D013997:Time Factors; D014765:Viral Vaccines; D017201:Virus Shedding
D000914:Antibodies, Viral; D014765:Viral Vaccines