BVDV is one of the commonest causes of infectious abortion. It is also associated with a wide range of diseases from infertility to pneumonia, diarrhoea and poor growth. BVDV is normally the most important viral cause of disease in cattle in the UK (at least outside of an FMD outbreak!)
What is BVDV?
BVDV is a member of the family of pestiviruses. Other diseases associated with other pestiviruses include classical swine fever and border disease in sheep. Pestiviruses infect cloven-hoofed stock only, BVDV has been found in pigs and sheep (indeed many cases of border disease are caused by BVDV not border disease virus)
Calf diarrhoea
o Mild diarrhoea of a few days duration.
o This was the initial disease associated with BVDV but is rare as a syndrome in the UK.
o In the US a new type of BVDV has been identified associated with outbreaks of severe diarrhoea with very high death rates.
- Mucosal disease
o Sudden onset weight loss and inappetance in cattle between 6 and 24 months of age (usually 12 to 18)
o Drooling and salivating
o Profuse foul smelling diarrhoea
o Usually only one or two animals infected at any one time
o Erosions and reddening on gums, cheek, tongue and muzzle
o Over 90% die within 7 days
o Only occurs in calves persistently infected while in the uterus with BVDV - Unthrifty calves
o Small at birth or fail to grow properly
o May be blindness, incoordination
o Hair loss or abnormal hair
o Other defects such as bulldog face can be present - Calf pneumonia
o BVDV infection suppresses the immune system, so calves with BVDV have a significantly higher risk of developing viral pneumonia
o Pneumonia generally more severe than that caused by infection with other viruses alone - Infertility
o Infection <16 days after service – apparently normal return to oestrus but reduced herd pregnancy rate
o Infection >16 days after service, but in early pregnancy – embryo loss and delayed return to oestrus
o Infection mid to late pregnancy – abortion or stillbirth
o Not all pregnant cattle infected by BVDV will show infertility, some will fight off infection and have normal calves
o Other cattle, particularly if infected before 120 days, will have apparently normal calves but these calves will be
persistently infected spreading the virus and being at high risk of developing mucosal disease. These animals are often referred to as PIs
Diagnosis
- BVDV causes such a wide range of disease it is rare to be able to diagnose cause on clinical signs alone (except for IBR infections which can have a characteristic conjunctivitis)
- Testing the blood for antibodies and/or virus is the best method of diagnosis.
- A paired blood sample for antibodies is useful for pneumonia, diarrhoea and infertility. If the first sample is taken when the animal is ill and the second two to three weeks later, a rise in antibodies suggests that there was active infection
- For most cattle with mucosal disease there will be no rise in antibodies. However, because they are persistently infected with BVDV, their blood will be virus positive
- Some unthrifty calves will show a rise in antibodies, others will have virus in the blood, but some will have neither. In the latter case a diagnosis of BVDV is made on the presence of other animals excreting virus or having raised antibodies.
Prevention and control
There are two routes for control.
The first and best is to eliminate BVDV from the herd by testing and slaughtering. In most herds BVDV is spread by PIs. Getting rid of these PIs and closing the herd can be significantly economically beneficial. Discuss with your vet the testing options, which can include testing the milk for virus and antibodies as well as the more routine blood testing. The problem with this route is that it may take two or more attempts to eliminate BVDV from the herd and becoming closed is vital because as BVDV is extremely common
The second route is vaccination. This can be used in combination with blood testing. There are two vaccines available in the UK for adult cattle, both of which claim to prevent the effects of BVDV on fertility. Ask your vet for advice as to which vaccine to use and when to use them