Outbreak of BVDV-1b associated with persistent infection, reproductive losses, and congenital malformations in beef cattle in Southern Brazil.

An outbreak of bovine viral diarrhea virus (BVDV) in a herd of 218 beef cattle resulted in 15 late-term abortions and the birth of two weak calves. Neonate 1, at 28 days of age, exhibited ataxia and paresis, while Neonate 2, at one day of age, was underdeveloped. Neonate 1 presented with cerebellar hypoplasia, hydrocephalus, and porencephalic cysts. Histological examination revealed foliar dysgenesis and ectopic Purkinje neurons. Neonate 2, weighing 7 kg at birth, showed no histologic lesions. A single fetus at six months was necropsied and showed no gross lesions. However, histopathology revealed multifocal lymphoplasmacytic inflammation. Tissue samples from the neonates and fetus were tested for BVDV by RT-PCR, yielding negative results. Brain tissue was tested by RT-PCR for Simbu serogroup viruses and by PCR for Neospora caninum and Toxoplasma gondii, all of which returned negative results. The entire herd was subjected to serum sampling for BVDV testing by RT-PCR. Six calves tested positive in all three consecutive rounds of testing, while one calf tested positive only once. Sera from the seven RT-PCR positive calves were subsequently tested by ELISA for antigen detection, with six testing positive. They were also tested by ELISA for antibody detection, with two calves showing seropositivity. Amplification products from three samples were submitted for Sanger sequencing and phylogenetic analysis, which identified BVDV-1b with 100% homology among the three sequences and a high similarity to Chinese strains. This study reports an outbreak of persistent infection by BVDV-1b in southern Brazil, with associated congenital malformations and reproductive losses.