Bovine Viral Diarrhea

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Bovine Viral Diarrhea

Introduction

Bovine Virus Diarrhea (BVD) is a worldwide disease that causes mild fever, diarrhea and leukopenia but may also cause fatal hemorrhagic diarrhea. 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.

Cause

BVD virus is closely related to hog cholera virus and ovine border disease virus, all belonging to the genus Pestivirus. 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. The clinical outcome of an infection depends on the time of infection as summarized in the table below.

Time of Infection Clinical Outcome
First 3 months of pregnancy Reabsorption or Abortion, History of repeat breeding with increased interval between estrus
42-145 days If fetus survives, calf born persistently infected with BVD virus
75-150 days Congenital defects: cataracts, retinal degeneration, optic neuritis, skeltal malformations, growth retardation
Late in Pregnancy Calves born with precolostrum antibodies to BVD virus

Diagnosis

Most BVD infections are subclinical with no observed symptoms other than an elevated titer. Abortions occur long after the initial infection and the aborted fetus should be submitted for diagnostic tests. Blood samples can be evaluated for virus isolation in animals suspected of acute infection. Paired samples 30 days apart are required to determine four fold increases in antibody titer. In addition, swabs from nasal or mucosal surfaces can be tested for virus isolation. Aborted fetal tissue and suspected BVD induced congenital defect calves should be tested for both virus isolation and antibody titer. Animals with persistent infection are identified by virus isolation in samples taken 30 days apart. Herd screening can be done by testing a bulk milk sample for BVD by RT-PCR. A negative result does not rule out BVD.

Treatment and Control

There is no treatment to "cure" BVD. Persistently infected animals must be identified and culled. A closed herd or long term quarantine of newly purchased animals can prevent infections. Modified live virus and killed virus vaccines are available depending on the situation.

Other Links

Novartis BVD Funamentals

Washington State University - BVD testing

USDA BVD Information Sheet

YouTube Video on BVD (Cast Pharma)

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