Infection leads to immunosuppression and can cause signs in multiple body systems in addition to the digestive tract.
Clinical disease associated with BVD virus infection is most common in young cattle (6–24 months old). The clinical presentation can range from inapparent or subclinical infection to acute and severe enteric disease.
BVD is transmitted in a number of ways. Either through a congenital infection of the fetus or after birth. Cattle that are acutely or persistently infected with BVD virus shed the virus in nasal and oral secretions, urine and feces. The virus gains entrance through mucosal membranes and replicated in the epithelial cells. The virus spreads systemically throughout the blood stream, both as free virus in the serum and in infected leukocytes.
It is possible for cattle to become infected via contact with contaminated fomites, such as water buckets, calf feeders, feed bunks, IV equipment, nose leads, clothing or people and cattle trucks.
The incubation period is about three to five days. Signs of acute infection include fever, lethargy, loss of appetite, ocular discharge, nasal discharge oral lesions, and diarrhea. Chronic infection may lead to signs of mucosal disease. Sores or ulceration in the mouth and gums may be present, along with reduced milk production in cows.
The importance of BVD in reproduction is that the virus crosses the placenta and causes intrauterine infections leading to early embryonic death, abortion, congenital defects or persistently infected calves. BVD has been implicated in 2-7% of dairy cattle abortions but has no permanent effect on fertility. Some infected animals may die, while others will recover, usually within one or two weeks.
If pregnant animals recover, they may abort about 2 to 4 weeks after exposure, especially if they are in the second trimester of pregnancy.
Vaccination is routinely practiced for BVD due to the economic impact of the disease in beef and dairy production. Modified live virus (MLV) vaccines can provide reproductive duration of immunity.
Bovine viral diarrhea (BVD)
