BVD

Strict biosecurity measures and a robust herd health plan are essential to prevent introduction of BVDv into your herd; effective biocontainment measures are essential on those farms with active infection to reduce the costs of BVD and to, eventually, eradicate BVDv from the herd

Cause

The main transmission route is by direct contact with cattle persistently infected with BVD virus.  It needs only one persistently infected animal to be introduced into a susceptible herd to cause very significant financial losses.

Clinical signs

Cattle exposed to BVD virus may show few clinical signs, producing protective antibodies within three to four weeks. In some situations, BVD virus infection may temporarily lower immunity to other infectious diseases exacerbating these clinical infections particularly in young calves.

BVD virus infection may temporarily lower immunity to other infectious diseases such as

  • Salmonellosis
  • Respiratory infections,
  • coccidiosis

BVD virus during early pregnancy causes embryonic death and return to oestrus, foetal death/abortion, mummification of the foetus, birth defects of the nervous system and eyes, weak/premature calves, and live persistently-infected calves.

BVD virus is most important when it infects susceptible breeding cattle during early pregnancy causing foetal death/abortion, and weak/premature calves.

Infection of the foetus before 110/120 days of pregnancy results in the birth of a live calf but persistently infected (animal carries the virus for life).  This is caused by failure of the developing immune system of the foetus to function properly before 110 days.

After birth these calves carry the virus for life and act as a potent source of BVDV infection for in-contact susceptible cattle.  Virus infection (not necessarily before 110 days), may also lead to various defects of the developing foetus' eyes and brain.  These calves may be born blind and lack co-ordination, respectively. These calves should be culled for welfare reasons, as well as being a source of infection.

 

BVD virus during pregnancy may cause:

  • Embryonic death and return to oestrus,
  • Foetal death/abortion,
  • Mummification of the foetus,
  • Birth defects of the nervous system and eyes,
  • Weak/premature calves,
  • Live persistently-infected calves.

 

Virus infection after 150 days gestation usually has little effect with live calves born at full term.

BVD virus can be spread in semen of persistently infected bulls or in bulls experiencing acute BVD with transient virus infection.

BVD will lead to low pregnancy rate due to embryonic death or later foetal death/abortion.  Bulls are vigorously tested for BVD before entering AI studs. Testing for BVDv is essential for all purchased bulls prior to their use on farm.

In older animals acute BVDv infection can reduce milk yield, increase the risk of clinical mastitis and retained foetal membranes, and increase somatic cell counts.

Mucosal disease

Mucosal disease occurs when persistently infected animals (calves infected before 110 days of pregnancy) become superinfected with cytopathic BVD virus.  The cytopathic BVD virus usually arises from changes in the BVD virus within the PI animal.  Mucosal disease is most commonly seen in 6 to 12 month-old calves, and is usually seen as sudden onset depression, fever and anorexia, with excess salivation.  Ulcers appear in the mouth and on the muzzle. There are purulent discharges from the eyes and nostrils. There is profuse diarrhoea with shreds of gut mucosa/blood present during the terminal stages.  There is rapid weight loss followed by death within 5-10 days.

Diagnosis

Acute BVD infection:

Paired blood samples 3-4 weeks apart to demonstrate rising antibody levels to this virus.

Persistent infection:

PI calves may be clinically normal but commonly present as chronic "ill thriven" or stunted calves due to their susceptibility to bacterial infection such as pneumonia. Testing for virus will identify PI calves. Two virus positive samples taken 3-4 weeks apart will confirm persistent infection, but in the vast majority of cases, particularly in ill-thriven calves one positive test is enough. Virus testing can be done via the blood or, particularly in calves < 12 weeks off age, skin (usually a plug of tissue from the ear). Skin testing is useful in younger calves because detection of the virus is not impaired by the presence of antibodies from the colostrum which may be present in the blood.

 

 

General principles of disease control

Biosecurity and biocontainment are terms describing programs for infectious disease control.

Biosecurity - reduce/prevent the introduction of new diseases onto an operation from outside sources

Biocontainment - reduce/prevent the movement of infectious diseases on the farm once biosecurity has been breached

Biosecurity is the first measure to prevent introduction of disease onto your farm; biocontainment measures may limit the financial losses following introduction of disease onto your farm after management errors have allowed disease to enter.

Johne's disease, Bovine Virus Diarrhoea virus (BVDv), salmonellosis, tuberculosis, Leptospirosis, Infectious Bovine Rhinotracheitis (IBR) are some examples of infectious diseases that can be introduced onto your cattle farm and severely affect the financial viability of your beef or dairy cattle enterprise.

Biosecurity is the first measure to prevent introduction of:

  • Johne's disease,
  • Bovine Virus Diarrhoea virus (BVDv),
  • Salmonellosis,
  • Tuberculosis,
  • Leptospirosis,
  • Infectious Bovine Rhinotracheitis (IBR)

Key Principles of Biosecurity

  • Keep a closed herd
  • If buying in cattle - only purchase from BVDv accredited herds
  • If buying in cattle from non BVDv accredited herds blood  test and isolate before introducing to herd
  • Prevent contact with cattle on neighbouring farms - double perimeter fence