Bovine Viral Diarrhea
Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100
Reprinted from The Tracker, volume 4, issue 4, April 2000
Bovine Viral Diarrhea (BVD) has been diagnosed in bison but our knowledge of the disease in this species is limited because it occurs relatively infrequently. This article discusses how the disease affects cattle and discusses how to prevent it all species.
Bovine Viral Diarrhea (BVD) is a contagious and potentially fatal disease of cattle that can also affect elk and bison. In cattle it causes death, reproductive losses, increased incidence of other diseases, and slow growth. It appears that bison are affected much the same as cattle while elk are more resistant to the virus. Elk that are infected can shed the virus and form antibodies to it but don’t seem to get sick. There is one report of the virus causing abortion in some elk cows. My discussion will be based on our understanding of the disease in cattle. Prevention of the disease in all species would follow the same principles.
As the name implies Bovine Viral Diarrhea is caused by a virus. There are two types of BVD virus: type 1 and type 2 and numerous strains within each type. Type 1 BVD is less severe and is the form that is typically seen in western Canada. Animals that come in contact with this virus generally develop a mild form of the disease consisting of fever, poor appetite and diarrhea. This often passes in a few days and many times it is not even noticed by the owner. This transitory BVD causes problems in a couple of ways. The first problem occurs when an infection occurs in a pregnant animal because it can spread to the unborn fetus. Different outcomes occur depending on the stage of pregnancy. Infection in the first part of pregnancy can result in embryonic death, abortion, mummified fetuses, or birth defects. If the fetus is infected in the middle of the pregnancy it can become a carrier of the virus. The calf's immune system does not recognize the virus as a foreign material and therefore will not try to destroy it. These calves appear normal at birth and continue to shed the virus throughout their life. Almost all of these calves will come down with Mucosal Disease (a form of type 1 BVD) before they are 12 months old. They develop fever, diarrhea, sores in their mouth and die in a few days or weeks. A small number of these carrier animals survive to maturity and continue to be a source of infection to other animals.
The second problem with transitory BVD is that it can make the animal more susceptible to other diseases by suppressing the immune system. In most cases this is not a problem but if the animal is in a stressful situation or exposed to a lot of other pathogens at the same time, it can develop other diseases such as pneumonia.
A newer form of the disease (Type 2) has been seen over the past 10 years in Eastern Canada and US. This virus has the ability to cause severe disease and death in both adults and calves. There were many herds with high death losses in all age groups several years ago but the same disease syndrome hasn't been recognized in Western Canada yet.
Prevention of the disease involves vaccinating your herd and limiting exposure to the virus. Vaccinating your herd is the most important step in BVD prevention. In a herd that has been well vaccinated the chance of BVD becoming a problem is minimal. For this reason, I recommend that BVD vaccination be a part of every bison producers herd health program. Vaccination of elk could also be considered if the chance of exposure is high. Remember to use the vaccines properly because the herd must be properly vaccinated in order for your protection to be effective.
Limiting exposure to BVD can be difficult to accomplish unless you operate a closed herd that has no contact with other bison, elk, or cattle. The virus can spread by fence line contact or by bringing persistently infected animals into your herd. To minimize the chance of introducing BVD into our herd, keep new additions separate for a few weeks to be sure that they are healthy before putting them in a pasture with your own animals. Another option is to blood test new animals to determine if they carry the virus before they are mixed with your herd. Consult you veterinarian to determine the best way to prevent BVD in your herd.