High prevalence of picobirnavirus genogroup I in calves without association with diarrhea in a dairy cattle herd, southeast Brazil

Dairy farming is one of the most widespread agricultural activities in Brazil. Neonatal diarrhea remains a major challenge, contributing significantly to economic and production losses in Brazilian dairy cattle herds. Picobirnavirus (PBV) has been suggested as a potential viral agent associated with calf diarrhea. This study aimed to detect PBV genogroup I (GI) RNA in fecal samples from calves in a closed high-producing dairy herd in São Paulo, southeastern Brazil. A total of 122 fecal samples were collected from 30-day-old calves, including diarrheic (n = 16) and non-diarrheic (n = 106) animals. Nucleic acids were extracted and analyzed using reverse transcription-polymerase chain reaction (RT-PCR). PBV GI was detected in 54.1% (66/122) of the samples, with the majority in non-diarrheic calves (87.9%; 58/66). The detection rate was 50.0% (8/16) in diarrheic calves and 54.7% (58/106) in non-diarrheic calves, with no significant association between PBV GI presence and fecal consistency (p = 0.72). Two RT-PCR amplicons from fecal samples collected on different days were sequenced to confirm detection of PBV GI; however, only one nucleotide (nt) sequence presented sufficient quality for analysis. Phylogenetic analysis revealed that this sequence clustered within PBV GI and shared the highest nt identity with a raw sewage sequence (93.4%), two human sequences (87.8-89.8%), and a monkey sequence (88.8%). These results confirm the circulation of PBV GI in a dairy herd and suggest that its presence is not associated with calf diarrhea. Further studies are needed to clarify the epidemiological and biological significance of PBV GI in cattle, as well as its impact on animal health and production.