Overview of Bovine Viral Diarrhoea
BVD is a member of the genus Pestivirus of the family Flaviviridae. It is also referred to as mucosal disease and is related to classical swine fever in pigs and border disease (hairy shakers disease) in sheep. It has a wide range of clinical signs due to the immunosuppressive nature of the disease. One of the key indicators of BVD is fertility issues and reproductive losses (for more information on possible causes of open cows click here). BVD has also been indicated as a major contributor to instances of Bovine Respiratory Disease including Infectious Bovine Rhinotracheitis (IBR).
The Impact of BVD infection during pregnancy
A transiently infected (TI) animal is currently infected with the BVD virus. As part of the normal immune response to a virus it will create antibodies to fight the virus, after a few days these can be detected by testing. A transiently infected animal may very early on test positive for antigen (the virus) but negative for antibodies (the immune response), however after a few days would test positive for both antigen and antibodies. Transient infection usually lasts for two to three weeks before the animal recovers. TI animals may suffer from poor appetite, depression, diarrhoea, nasal discharge, decreased milk production, reduced fertility and immunosuppression which may lead to other infections (in particular BVD has been indicated as a major contributor to instances of respiratory disease). However, a TI animal may also show few or no signs of infection. TI animals are infectious and will spread BVD, however the main vector of the disease is Persistently Infected (PI) animals.
After two to three weeks the animal which has been transiently infected has launched an immune response and has recovered. After this time it will test negative for antigen, as it does not currently have the virus, but positive for antibody, as it has developed immunity to BVD as a result of the previous infection. These animals are often referred to as seroconverted (seroconversion refers to the time period when an antibody can be detected in the blood). This immunity (or period of seroconversion) will likely last for several years but is not thought to last for the lifetime of the animal.
A naïve (or susceptible) animal is an animal that has no antibodies to BVD and therefore no immunity. If not vaccinated naïve herds are susceptible to potentially devastating outbreaks of BVD if they come into contact with the virus.
Outbreaks caused by transiently infected (TI) cattle tend not be as severe because these animals shed much lower amounts of virus for only a few weeks’ time whereas persistently infected (PI) cattle will continue to shed large quantities of virus until they are removed. The worst timing for a BVD infection is during mating/pregnancy as this provides the greatest risk of creating PI calves. Unless recognized and controlled early PI calves can lead to a chronic BVD issue in the herd, resulting in more and more PI calves each year. For this reason pre-mating testing of bulls and herd screening is recommended. Click here for more information on BVD testing procedures.
IDEXX BVD tests are used all over the world and IDEXX has been heavily involved in several eradication programs in Europe. We have a wealth of global expertise and resources to call on when addressing BVD.
See below to watch a video produced by IDEXX in America which explains the different types of infections.
If you want to know more about BVD IDEXX have produced a series of videos with BVD expert Dr Enoch Bergman who operates out of Esperance in Australia available below
A key resource for BVD is BVD free New Zealand click here to go to their website