Causative agent: Bovine Herpes Virus
IBR is very common in cattle. It is also seen in white-tailed deer, mule deer, and antelope (9). Nasal exudate, semen and fetal fluids spread the disease. Aerosol spread from coughing is thought to be the most important method of transmission (9).
A serologic survey of bison from Yellowstone National Park in Wyoming in 1991-1992 demonstrated antibodies in 31% of bison tested (26).
Clinical signs:
The clinical signs of IBR in bison have not been described. In cattle, IBR often occurs in very explosive outbreaks (9). It is very contagious, 100% of the animals in a herd can be infected. Clinical signs in cattle include: fever, anorexia, reddening of the nasal mucosa, ocular discharge, nasal discharge, an increase in respiratory rate, and a cough. Some animals may develop reddened eyes that may be mistaken for pinkeye.
Cattle less than 1 week of age may develop a systemic form of the disease that is associated with a very high mortality rate. Cattle less than 6 months of age can develop encephalitis, characterized by incoordination and convulsions associated with a high mortality rate. In adult cattle, abortion is a common sequella of the disease, occurring up to 90 days after infection.
Postmortem findings:
The pathological changes associated with IBR in bison have not been reported. Postmortem findings in cattle include lesions in the nasal cavities, pharynx, larynx , trachea, and on the muzzle (9).
Diagnosis:
The virus may be isolated in swabs taken from nasal and ocular exudate. Most commonly the diagnosis is made on postmortem examination of aborted fetuses and submission of samples or the whole fetus to a pathology laboratory for histopathology and virus isolation.
Blood testing may be done to detect rising titers to IBR virus. Two blood samples must be taken 2 to 3 weeks apart.
Treatment:
Protocols have not been reported for treating IBR in bison. Because of the contagious nature of the virus, infected bison should be separated from non-infected bison. In cattle, vaccinating with a modified live intranasal vaccine in the face of an outbreak may reduce the spread of the disease (9).
Control:
There have been no protocols reported for controlling IBR in bison. In Canada and the United States there are many commercially available modified live and killed IBR vaccines. None of them have been approved for use in bison. Most of these vaccines provide good protection against the occurrence of IBR in cattle, but their efficacy in bison has not been established.
The effect of modified live virus IBR vaccines on young bison has not been studied. Because of this it may be advisable to refrain from using a modified live IBR vaccines on recently weaned bison calves.
The nature of killed virus vaccines is such that a booster vaccine must be administered roughly 3 weeks after the initial vaccination in order for adequate protection to be provided. Meeting these requirements for recently weaned bison calves may be difficult. The stress associated with handling of bison is greatest in bison calves at the time of weaning.
Also, the injuries and mortalities associated with handling of bison is greatest in bison calves of weaning age.
Killed virus vaccines should be administered to bison on a yearly basis in order to provide adequate protection. Modified live virus, intramuscularly administered IBR vaccines may provide adequate protection to bison. The duration of the protection is unknown , but it may not be for the entire life of a bison.
Modified live virus, intranasal, IBR vaccines provide adequate protection to cattle. They are difficult to administer properly to bison. If they are to be used in bison it may be prudent to vaccinate the entire herd every year or every second year to ensure that all animals are vaccinated adequately.