F100
Bovine Viral Diarrhea (BVD)

Introduction/Causative Agent: BVD is the name of a group of diseases in cattle of all ages that are caused by the Bovine Viral Diarrhea virus. The virus has at least two strains or genotypes, Type I and Type II; and two biotypes, cytopathic (CP-BVD) and noncytopathic (NCP-BVD). The cytopathic and noncytopathic terminology relates to how the different biotypes behave in cell cultures in the laboratory. For example, the CP-BVD virus will destroy/damage cell cultures, while the NCP-BVD will not. Infected animals are also classified as persistently infected (PI) or have the mucosal form of the disease. PI animals are ones that were infected before birth (during day 110-120 of the pregnancy) and survived. PI animals continually shed the virus throughout their lives contaminating their own offspring during pregnancy, other animals, and the environment.

Clinical Signs: The signs associated with BVD depend on the age of the animal at first infection and the genotype they are infected with. Some animals can even be infected with the NCP-BVD at first and then become infected with the CP-BVD later. Five different forms of the BVD disease are often described:

1. Peracute BVD Disease: This is a very fast acting form of BVD, usually caused by Type II NCP-BVD viral infection. It can occur in almost any age of animal. In this form of the disease, the animal has a very high fever (106-110 degres farheniheight) and can sometimes cause respiratory problems, diarrhea, and not eating (anorexia). These animals will often die within 48 hours of the initial infection.
2. Acute BVD Disease: Acute BVD is also a relatively fast acting form of BVD. It can be cause by either biotype of BVD (NCP-BVD or CP-BVD). Animals that develop this type of infection have a fever (104-106), diarrhea (sometimes bloody), and can have lesions or errosions on the muzzle and mouth. Most of these animals will survive the infection, but can easily develop secondary bacterial infections.
3. Chronic BVD Disease: This is more of a long-term BVD viral infection. It causes signs similar to the acute form of BVD; however, the signs are more severe and more of these animals will evenually die from the disease. In addition to the fever, diarrhea, and erosions, these cows will often show signs of weight loss, poor thrift, hair loss, a lack of appetite, poor production and nasal discharge.
4. Calves Infected Before Birth: The signs associated with unborn calf (fetal) infections depends on the age of the fetus. Most fetuses that are exposed to the BVD virus during the first 120 days of pregnancy usually die. The fetus is either mummified, resorbed (broken down and removed within the cow’s body), or aborted. Fetuses infected between days 110-120 often become persistenly infected (PI) animals.
   
   PI animals can look completely normal or may have severe disease. Many times the PI calves have poor hair coats, are smaller than other calves, and do not develop well. These PI animals can develop normally and eventually produce more PI offspring if they are used for replacement animals. Other signs associated with BVD infections include blindness, bone and joint deformities, underdeveloped brains, weakness and diarrhea. If the fetus is infected after it is 120 days old, it often survives and can be a normal, healthy calf.
5. Mucosal BVD Disease: The mucosal form of BVD infections is often caused with a NCP-BVD animal becomes infected with the CP-BVD biotype. The signs associated with this form of BVD are even more severe than the chronic BVD infections. Typical signs include hemorrhage (blood) from the rectum and areas of hemorrhage in the membranes of the mouth and vulva. The bleeding is caused by lesions/erosions that form throughout the digestive tract from the muzzle and mouth out through the intestines and colon. Animals with mucosal disease seldom survive. Type II BVD is most often associated with PI animals and mucosal disease.

Disease Transmission: The virus usually enters through the nose or mouth from direct contact with infected animals or by contact with contaminated objects (boots, vehicles, etc.). Food and water sources that are contamined with manure that contains the virus are a very big source of infection. Other ruminant animals such as buffalo, deer and antelope can also carry the BVD virus. When a pregnant animal is infected, the virus spreads to the fetus causing an abortion, defects, or PI animal.

Diagnosis: Virus isolation of BVD from tissue samples or from an aborted fetus can be used to identify infected animals or herds. Blood samples can be used to find titers and signs of infection. Recent studies indicate that BVD can be detected from milk samples using PCR amplification. New skin tests are also available to detect PI animals.

Treatment: There is really no direct treament for BVD infections. All that can be done is to support the infected animal with fluids, antibiotics (to prevent secondary bacterial infections), vitamin B, and adequate nutrition.

Prevention: Aggressive vaccination programs, utilizing a combination of modified live and killed vaccines, are effective in preventing and controlling the disease. However, these vaccines may not totally prevent fetal infections. Therefore, it is recommended that infected and PI animals be identified and culled as soon as possible.

References: VM121, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. December 10, 2004, E. J. Richey, DVM.