Veterinary Preventive Medicine-II

DIAGNOSIS

•  Clinical diagnosis is a complex problem. Signs of the different syndromes may appear alone or in combination.
• Although many of the signs are similar to RP, the mortality in that disease is much higher.
• The oral lesions are very important, but their absence does not exclude BVD.
• This disease must be differentiated from conditions in cattle causing diarrhoea, erosions/ulcerations of the gastrointestinal tract, reproductive failure, teratology, skin disease, laminitis, poor growth and respiratory tract disease such as vesicular diseases, ingestion of caustic substances, mucosal disease complex: Rinderpest, bluetongue, papular stomatitis, malignant catarrhal fever.

Laboratory diagnosis

• Samples to be collected- nasal, ocular discharges, blood, spleen, lymph nodes, lungs, and liver
• Identification of the agent- Persistently viraemic healthy animals resulting from congenital infection can be readily identified by isolation of noncytopathogenic virus in cell cultures from blood or serum.
• It is necessary to use an immune-labelling method to detect the growth of virus in the cultures.
• Alternative methods based on direct detection of viral antigen or viral RNA in leukocytes are also available.
• Persistence of virus should be confirmed by resampling after an interval of at least 3 weeks.
• These animals will usually have no or low levels of antibodies to BVDV.

Serological tests

• Acute infection with BVDV is best confirmed by demonstrating seroconversion using sequential paired samples from several animals in the group.
• The testing of paired sera (acute and convalescent samples) should be done a minimum of 21 days apart and samples should be tested side by side.
• The enzyme-linked immunosorbent assay (ELISA) for antibody and the virus neutralization test are the most widely used. Demonstration of the BVDV by CPE (but many BVDV strains do not produce CPE), FAT, PCR a much more productive method, are necessary for definitive diagnosis.