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Bovine Viral Diarrhea (BVD) Virus

Disease Facts
  • Fluid / Aerosol borne disease caused by Bovine Viral Diarrhea virus
  • Approximately 10 – 15% of U.S. dairy herds have some incidence of BVD
  • Infection results in estimated milk productions loss of $330 to $494 million per year in the U.S., or $1.93/hundredweight, based on a herd size of 150 cows
  • Negatively impacts respiratory, digestive and reproductive systems
  • Losses result from inhibited immune function leading to additional secondary infections, directly and indirectly reduced milk yield, decreased reproductive performance and increased calf morbidity and mortality
  • High risk herd characteristics include: recent expansion, untested additions; no vaccination program; poor reproductive performance; abortions and unthrifty calves; lingering respiratory challenges; recent testing evidence of BVD; frequent cattle movement
  • Vaccination cannot provide complete protection because of continually evolving viral strains, and potential gaps in coverage over an animal’s lifespan.
  • Infection occurs in two forms, persistent and acute:
    • Acute Infection
      • Transmission has occurred outside the critical gestational period
      • Transient infection lasts approximately 3 weeks
      • Infections result in sub-optimal immune function enabling other health challenges (respiratory, reproductive, etc.)
      • Acute outbreaks, identified by abortion storms, fever, depression and diarrhea, are caused by exposure to PI or acutely infected animals
    • Persistent Infection
      • Occurs only in the fetus, during a specific window of development
      • The fetus’s developing immune system cannot recognize BVD virus as foreign, and does not produce a ‘normal’ immune response
      • Infection causes many immune problems; 50% of PI’s die within the first year, and less than 10% survive over two years
      • Survivors continually shed BVD organism into the environment

Virus transmission and control:

  • Transmission can occur vertically and horizontally
    • Vertical transmission:
      • If the dam is introduced to a new strain of BVD virus between 45 and 125 days of gestation her calf will become persistently infected
    • Horizontal transmission:
      • Transiently infected animals shed virus 4 to 10 days, PI’s shed virus throughout life
      • Virus can be shed from all bodily secretions (nasal discharge, saliva, semen, urine, milk and feces)
      • Virus can be transmitted on infected equipment, animal or environmental contact, even in aerosolized (coughed) particles over short distances
      • Virus remains viable in the environment less than two weeks
      • Less than one hour of contact with PI is sufficient to transmit virus, acutely infected animals are not as efficient at transmitting the virus.
  • Control is supported by proper management: good animal hygiene and biosecurity practices
    • Immediately remove any PI positive animals
    • Minimize human vectored transmission by disinfecting equipment and using disposable supplies only once (needles, sleeves, etc.)
    • Minimize animal to animal transmission by quarantine and testing of all herd additions as well as optimizing stocking rates in barns and holding areas
    • Minimize environment to animal transmission by cleaning maternity areas and reducing the number of biting insects

Testing:

  • Infected animals can be detected by the presence of viral RNA in fresh or preserved milk samples (bulk tank or group milk testing) OR by presence of antigen (a molecule that stimulates a response from the immune system) in milk, tissue or serum
  • Begin BVD control programs by surveying the milking herd using bulk tank or group milk tests
    • Perform tests every four months until all cows are represented in screened samples
    • Bulk tank or group samples can detect one PI in a pool of up to 250 animals
    • If your herd IS NOT at high risk of having a BVD outbreak these screens may be sufficient
    • If your herd IS high risk, continue bulk tank/group testing, following up on any positive bulk tank results with individual animal (milk or serum sample) testing, and implement a calf testing program (tissue samples can be collected at birth or any time thereafter)
    • Calf testing is critical to controlling BVD outbreaks because so many PI calves do not survive to adulthood
    • Continue testing programs until herd is no longer considered ‘high risk’
    • Follow-up any positive individual animal sample (milk, tissue or serum) with another test in 3 weeks to rule out the possibility of acute (transient) infection
Copyright © 2002 by [NorthStar Cooperative, Inc.] All rights reserved. Revised: 7/9/07