Oesophagoscopy and detection of viral nucleic acids in oesophageal biopsies--A contribution to BVDV diagnosis.

The endoscopic appearance of the oesophagus of animals infected with bovine virus diarrhoea virus (BVDV) but without signs of acute mucosal disease (MD) was investigated for any common or 'early warning' lesions. Thirty-seven BVDV-infected animals [36 persistently infected (PI) and one transiently infected] were examined clinically and endoscopically for typical erosions of the oronasal and oesophageal mucosa, respectively. During oesophagoscopy, mucosal biopsies were taken and tested for pestivirus-specific nucleic acids by reverse transcription polymerase chain reaction (RT-PCR). The results were compared with those of RT-PCR with various sample materials (blood, nasal and conjunctival swabs and faecal samples) usually used for routine diagnosis of BVDV infection. The average age of the 36 PI animals was 13.5 months, eight animals were 24 months or older. None of the PI animals had clinically visible erosions of the oronasal mucous membranes. During oesophagoscopy, all animals showed a reddening but unexpectedly no erosions or ulcerations of the oesophageal mucosa. Although in 21 of 36 PI animals all samples tested positive, the oesophageal biopsies were with no exception constantly RT-PCR positive in contrast to all other materials investigated. Remarkably, in the transiently infected animal all samples tested negative except for the oesophageal biopsy. Hence, this infection would have been missed by conventional diagnostic sampling.