Bovine Virus Diarrhea Virus / Peste Virus
This is a disease which has been around in the cattle industry for a long time, but regarded as a disease which only occasionally causes a problem. In recent year’s there has been a lot of discussion about the effects of this disease on production in our dairy and beef herds. It has become a disease that is talked about a lot more than in the past- why? The answer is that some countries have eradicated the disease, others have started eradication programs and some have set up control programs. Therefore it may one day have an impact on our export markets. Also this disease can have significant economic impact when introduced into a herd, and can be the underlying problem in many herds. Producers have become so aware of it that they are using it in bull sale catalogues to market their animals as BDV free.
The disease is caused by a virus called pestevirus. The virus can cause two different diseases 1) BVDV or BVD 2) mucosal disease. There are different strains of the virus some more aggressive than others but all cause significant disease.
The disease is widespread throughout Australia. In some areas there is greater knowledge about the prevalence than there is in other areas. Overtime herds become naive to the virus and when a carrier animal is brought into the herd a ‘train wreck’ occurs. In other herds the virus is active as carriers are in the herd keeping the virus going and causing low grade problems. In the second instance the disease may go unnoticed, but the economical impact can be significant.
Signs of infection;
Poor fertility or conception rate (usually detected at pregnancy testing)
Weak or stunted calves
Abnormalities of the brain and eyes of newborn calves
Lesions on the nose and mouth (mucosal disease)
If young non-pregnant animals become infected some may not show signs of the virus but instead there will be an increase in bacterial infections as the bacteria take advantage of the suppressed immune system. Hence pneumonia, diarrhoea, BRD, footrot etc become more prevalent.
If infection occurs at mating time the animal is unlikely to conceive and is also susceptible to bacterial infections.
If a pregnant cow is infected the cow herself will have symptoms of those of the non pregnant animal. The fetus maybe aborted, be born deformed, or maybe a carrier calf depending on the age of the fetus when the cow is infected.
A carrier calf occurs when the cow is infected during the 2nd trimester of pregnancy. At this stage a calf’s immune system is not yet established. When the immune system forms it recognises the virus as part of the calf rather than foreign. The calf is therefore born normal and sheds the virus in its body secretions. The calf is known as a carrier or a PI, persistently infected.
This calf can infect other animals in comes into contact with.
What is mucosal disease?
This occurs when a PI/ carrier of peste virus becomes infected with a second more aggressive strain of the virus. Most carriers are affected in the first 2 years of life. The animal then wastes away until death. There maybe diarrhoea, or lesions on the nose and feet.
How is the disease diagnosed?
Usually there is a reason to be suspicious ie. abortions or poor results at pregnancy test.
A blood test for antibodies can be carried out on a random sample from the herd. The blood results can give an indication of whether the herd has been infected and a rough time line as to when infection occurred. In this test carriers come up as negative as their immune system does not produce antibodies.
If the above result indicates recent infection within the herd an ear notch sample from each animal is used to identify the carrier animal. The carriers can be then removed from the herd.
Control methods within a herd;
1) biosecurity; once cleared of BVD a test can be conducted on animals brought into the herd. Fence lines should be maintained. Cattle should not be mixed with cattle from other herds during the pregnancy, this includes showing cattle. Infection of the dam could result in a carrier calf being born.
2) autovaccination is when a carrier animal is used to expose stock at a young age (before mating) to the virus to produce an immune response and reduce chances of problems during mating/pregnancy. This may only protect against one strain of the disease and leave the animal susceptible to other strains.
3) Vaccination. Pfizer have produced a vaccine against the disease.
If you are concerned about this disease in your herd, please contact the vet clinic as a blood test of 10 animals can help to provide you with some answers.