Natural Outbreak of BVDV-1d-Induced Mucosal Disease Lacking Intestinal Lesions

Bovine viral diarrhea virus (BVDV) belongs to the Pestivirus genus, which is further divided into subgenotypes (1a-1u and 2a-c). When persistent infection occurs, the calf will be immunotolerant to BVDV and possibly develop mucosal disease. This study describes an outbreak of BVDV-1d-induced mucosal disease lacking intestinal lesions. Eleven calves presented with anorexia, sialorrhea, lameness, recumbency, and death. Three calves were necropsied, showing ulceration of the interdigital skin and the oral and nasal mucosa; linear ulcers in the tongue, esophagus, and rumen; and rounded ulcers in the abomasum. Microscopically, mucosa and skin had superficial necrosis, with single-cell necrosis and vacuolation in epithelial cells, and severe parakeratosis. Immunohistochemistry (IHC) showed BVDV antigen in the cytoplasm of epithelial cells in skin and mucosa. All 11 dead calves were positive upon reverse transcription-polymerase chain reaction (RT-PCR) for the detection of Pestivirus along with another 11 live calves from the herd, which were positive again by RT-PCR and IHC after a 4-week interval. Sequencing of the 5' untranslated region and N-terminal protease showed that viruses from these 22 calves were homologous and of subgenotype BVDV-1d. Cytopathic BVDV was isolated from 8 of 11 dead calves, but only noncytopathic BVDV was isolated from the 11 live animals. The findings indicate that this was an outbreak of mucosal disease caused by BVDV-1d, with high morbidity, and lesions restricted to the upper alimentary system and skin and absent from intestine. Thus, the epidemiological and pathological features in this form of mucosal disease may be similar to vesicular diseases, including foot and mouth disease.