Bovine Viral Diarrhoea Virus

Species

Other Names

Mucosal Disease
Pestivirus

Syndromes

Description

This is a widespread viral infection capable of causing a range of different conditions. In healthy, non-pregnant cattle, bovine viral diarrhoea virus (BVDV) 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), BVDV infection can increase susceptibility to other respiratory disease agents and increased severity of resulting disease.

BVDV infection of pregnant cattle may result in abortion, foetal deformity or delivery of normal and immune calves, and in some cases the birth of persistently infected (PI) animals. PI animals may show no signs of illness and yet may be lifelong shedders of the virus, acting as a source of infection for other cattle. If PIs are infected with a second strain of BVDV virus they may develop severe and often fatal Mucosal Disease (MD) (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 BVDV, while at the same time exposing cattle to potential stressors and a range of other infectious agents. Under these conditions, BVDV 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 or faeco-oral transmission in yarded cattle from mixed origins.

Ear notch or blood tests are often used to screen out persistently viraemic cattle from the livestock export process.

Clinical Signs and Diagnosis

Outbreaks of diarrhoea or abortion in recently mixed young cattle should raise suspicions of BVDV infection. Fever, lacrimation, nasal discharge, and erosion/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 MD have ulcers of the oral mucosa, muzzle, coronet, and interdigital space, resembling foot and mouth disease or malignant catarrhal fever. However, MD 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 a tissue sample (ear notch) or serum and whole blood, submitted chilled, for virus isolation. For serological testing, two serum samples taken 3-4 weeks apart are required. The preferred specimens from dead animals are spleen, ileum, and mesenteric lymph nodes, submitted chilled for virus isolation.

Treatment

PIs identified by ear notch or blood test should be sent for slaughter and cases of MD euthanised. Other transiently viraemic cattle will usually recover uneventfully after a week or so, although there may be an increased risk of bacterial respiratory disease, including pneumonia if other causal factors are present (see Pneumonia).

Prevention

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 BVDV status of these cattle is unknown. Deliberate mixing with a PI animal is sometimes used to immunise groups of non-pregnant cattle, although this method will not ensure that all animals in the herd have been exposed to the virus.