This is a wide spread viral infection capable of causing a range of different conditions.
In healthy, non-pregnant cattle, BVD infection typically causes mild, short-term disease (fever, depression and diarrhoea) and animals then recover and are immune.
In animals exposed to other stressors and disease agents (such as cattle in feedlots) BVD infection can increase susceptibility to other respiratory disease agents and increase severity of resulting disease.
BVD infection of pregnant cattle may result in abortion, delivery of normal and immune calves, and in some cases birth of persistently infected (PI) animals. PI animals may show no signs of illness and yet may be lifelong shedders of virus, acting as a source of infection for other cattle. If PIs are infected with a second strain of BVD virus they may develop severe and often fatal mucosal disease (fever, diarrhoea, and lesions on nose, mouth and feet).
The export process aggregates large numbers of cattle that may be susceptible (not previously exposed) to BVD, while at the same time exposing cattle to potential stressors and a range of other infectious agents. Under these conditions, BVD can spread rapidly through the population, and cause widespread acute (and short-term) disease, abortions in pregnant cattle being exported and may also predispose cattle to other diseases, particularly respiratory disease. The presence of a single PI in an export consignment may be enough to introduce virus into the mix.
Spread is mostly during close (nose-to-nose) contact of yarded cattle from mixed origins.
Blood tests are often used to screen out persistently viraemic cattle from the live export process.
Outbreaks of diarrhoea or abortion in recently mixed young cattle should raise suspicions of pestivirus infection. Fever, lacrimation, nasal discharge, and erosion and ulceration of the oral mucosa, coronary band and interdigital cleft may be present.
Differential diagnoses include coccidiosis, gastrointestinal parasitism, salmonellosis, indigestion, ruminal acidosis and bovine papular stomatitis virus.
Individuals within a group or mob that are noticeably stunted and scruffy may be PI animals. Cases of Mucosal Disease have ulcers of the oral mucosa, muzzle, coronet and interdigital space, resembling foot and mouth disease or malignant catarrhal fever. However, mucosal disease usually affects one or a few animals in a group whereas foot and mouth disease behaves as a fast moving outbreak with few cattle spared. Cases of malignant catarrhal fever are usually older, single animals and they have bilateral corneal opacity.
Laboratory confirmation requires clotted and unclotted blood for detection of antibodies and antigens. These must be submitted chilled. The preferred specimens from dead animals are fresh liver and spleen, submitted chilled for virus isolation and demonstration of antigen.
PIs identified by blood test should be sent for slaughter and cases of mucosal disease euthanased. Other transiently viraemic cattle will usually recover uneventfully after a week or so although there may be increased risk of bacterial respiratory disease including pneumonia if other causal factors are present (see pneumonia).
Testing animals prior to export may allow determination of disease status and identification of any PIs. A vaccine is available but may be more likely to be used in breeding herds before joining. Avoid mixing of susceptible cattle from different origins particularly if the BVD status of these cattle is unknown. Deliberate mixing with a persistently viraemic animal is sometimes used to immunise groups of non-pregnant cattle.