Bovine Viral Diarrhea Virus (BVDV)

BOVINE VIRAL DIARRHEA VIRUS (BVDV)

What is BVDV and What Diseases Does It Cause?

BVD is an RNA virus that is classified into two different genotypes known as type 1 and type 2. Within each genotype there are several different strains of BVD virus that can differ significantly in their ability to cause disease. In addition, there are 2 different biotypes of BVDV called cytopathic and non-cytopathic with 99% of the field strains of BVDV being non-cytopathic. Infection with BVDV is most often inapparent or subclinical, but the virus can cause one or more of the following problems:

Abortion or early embryonic death (most important)
Pneumonia
Fever (temperature 105*F or greater)
Diarrhea
Lameness
Immunosuppression

How is BVDV Infection Spread?

If BVDV has not previously been on the farm, the virus is usually brought in by replacement animals or their unborn calves. Replacement animals can shed the virus in the air, manure and in body secretions. Susceptible animals typically become ill 10-14 days after exposure and usually develop a fever with signs of pneumonia. Often animals will also develop diarrhea and occasionally have ulcers and erosions in their mouths. Pregnant animals may abort beginning as soon as 1 month after exposure. Sometimes BVDV is introduced into a herd by people with contaminated footwear and/or clothing and occasionally by fence line contact with your neighbor's cattle.

Persistently Infected (PI) or Carrier Animals

How does an animal become persistently infected with BVDV?
An animal becomes persistently infected with BVD virus if the fetus is exposed to a slow-growing, non-cytopathic strain of virus between days 30 and 125 of gestation. Fetuses exposed to BVDV after 125 days of gestation will mount an immune response against the virus (which clears the infection) and usually develop quite normally. Fetuses exposed to a rapidly growing or "hot" strain of virus are usually killed, and the dairyman notices abortions or early embryonic death. It is important to remember that a persistently infected or PI animal is the only permanent carrier of BVD virus. Animals that are exposed to BVD virus (acute disease) may become infected and shed the virus for a few days but recover and become immune.

Do PI animals shed a lot of virus?
Yes, PI animals shed several billion viral particles a day and serve as a reservoir of BVDV in a herd.

Do PI animals remain in herds for a long time?
Yes and No. Ninety percent of PI animals are culled from dairy herds before they reach 2 years of age but some PI animals can remain in the herd for several years. However, new PI animals are constantly developing as a result of fetal exposure to BVDV from PI animals. Remember that a persistently infected or PI animal is the only permanent carrier of BVD virus.

Can I tell a PI animal by looking at it?
Some PI animals are stunted and are poor doing but many appear normal and cannot be distinguished from non-PI animals. You must test an animal to determine if it is persistently infected with BVD virus.

Can't I control BVDV infection in my herd with a good strategic vaccination program?
Yes and No. Vaccination usually protects animals from disease (illness and death) but does not protect them from becoming infected with the virus (subclinical infection). Subclinically infected animals can shed the virus in their blood (viremia) and hence expose the fetus to BVDV.

How common are PI animals?
About 1% or less of all cattle tested at the Wisconsin Animal Health Laboratories (WAHL) are persistently infected with BVDV. However, studies indicate that approximately 15% of the dairy herds in Wisconsin contain at least one PI animal. Some of the PI herds tested at WAHL contained 5% or more PI animals.

How do I find out if I have BVD virus present in my herd?
If you suspect acute BVDV infection or if you are concerned about the possibility of a PI animal(s) being present in your herd contact your veterinarian. He or she will know the proper samples to sent to the laboratory to confirm BVDV infection. If your veterinarian has any questions, he or she may contact the Wisconsin Animal Health Laboratory in Madison 800-608-8387 or Barron 800-771-8387.

Prevention and Management

Do not purchase BVDV infected cattle, especially bulls. Test all replacement animals for persistent infection prior to admission to the herd. In addition, the unborn calves carried by the replacement animals should be tested for persistent infection soon after birth.
Isolate all newly purchased cattle for at least 30 days, preferably on another farm.
Purchase only animals from herds with a known effective vaccination program. Get specific information about the vaccination history such as what vaccine was used and when it was given. If killed vaccines were used, make sure that a primary series (two doses given a few weeks apart) was given.
Make certain your own cattle are properly vaccinated according to the manufacturer's recommendations before bringing new cattle into the herd. Consult your herd veterinarian when developing a vaccination program.
Control farm traffic. Do not allow people to enter your barn without wearing clean footwear and coveralls. For more detailed information about biosecurity please read Biosecurity for Dairy Farms.

Additional information can be obtained by contacting your local veterinarian or the Wisconsin Department of Agriculture, Trade and Consumer Protection, Division of Animal Health, Wisconsin Animal Health Laboratories (Madison 800-608-8387 or Barron 800-771-8387).