1. What is BVD?
Bovine viral diarrhoea, or BVD, is one of the most common viral disease in cattle. It is highly damaging and often results in a massive economic loss once it has infected a naïve herd. The virus which causes BVD in cattle is a Pestivirus from the family Flaviviridae. The round-shaped, single-stranded RNA virus is 40 to 50 nanometres in diameter and can occur in two different genotypes.
2. What are the genotypes of BVD?
BVD virus (BVDV) in cattle is known to have two genotypes - BVDV type 1 and BVDV type 2. They differ regarding their genetic substance.
3. What are biotypes?
BVDV in cattle comes in two biotypes: cytopathic (cp) and non-cytopathic (ncp). The majority of BVD viruses are ncp, e.g. they reproduce in cell cultures without visible effects to the cells. The cp biotype leads to apoptosis of the cells.
4. What are the clinical signs of BVD in cattle?
Up to 70–90 % of infections do not show any clinical signs and therefore go unnoticed. In other cases infected animals display diarrhoea, fever, mucosal erosions and a defective reproductive performance such as abortions, stillbirths and weak offspring. BVD in cattle also suppresses the bovine immune system rendering the animals more susceptible to other infectious diseases. In order to confirm the presence of BVD in cattle, lab tests are indispensable.
5. How is BVD transmitted?
BVD in cattle can be transmitted directly as well as indirectly. Indirect transmission can occur via any contaminated materials, e.g. needles or blood transfusions. Direct transmission mainly happens through direct contacts and occurs via acutely infected animals and even more importantly, via persistently infected (PI) animals. Acutely or transiently infected cattle may excrete the virus over four to ten days. PI animals shed the virus in large quantities throughout their lives. It can be found in blood, saliva, milk, faeces, urine and semen.
6. What is a persistently infected (PI) animal?
Persistently infected animals may develop after infection with the ncp-virus between the 40th – 120th day of gestation. During this time, the calves’ immune systems are not yet fully developed and the virus may therefore be accepted as non-antigenic. PI animals usually appear to be normal albeit a little smaller and weaker than their peers. PIs are more susceptible to infectious diseases, in particular mucosal disease.
7. What is mucosal disease?
PI animals which get in contacts with cytopathic BVD virus develop this invariably fatal disease showing clinical signs such as fever, anorexia, and violent bloody diarrhoea.
8. Is BVD harmful to humans?
BVD can only affect cloven hooved animals like ruminants and pigs and is not pathogenic to any other animal species, including man.
9. How can BVD in cattle be eradicated?
The management strategies concerning BVD in cattle include the removal of PI animals, biosecurity, and as part of if, vaccination. Furthermore, the vaccination of animals must induce broad and lasting immunity and the vaccination of female cattle needs to be safe during pregnancy and provide foetal protection.