Diarrheal pathogens in calves: Rotavirus and co-infection with Coronavirus and Norovirus in selected provinces of Iran

Calf diarrhoea is a leading cause of mortality and morbidity among neo-natal calves in the cattle industry, with viral pathogens such as bovine rotavirus (BRoV), bovine coronavirus (BCoV), and bovine norovirus (BNoV) playing prominent roles. Present study investigated the occurrence and co-infection pattern of BRoV, BCoV, and BNoV in diarrheic calves in seven main livestock- producing provinces of Iran. A total of 320 fecal samples from diarrheic calves were examined with ELISA and RT-PCR. The results revealed that BRoV was the most prevalent pathogen (68.8%), followed by BCoV (56.5%), and BNoV (25.9%). The most common co-infections were BRoV+BCoV (22.5%) and BRoV+BNoV (12.5%), whereas 6.9% cases revealed triple infection. Notably, BNoV mono-infection was rare (1.6%), suggesting its limited pathogenic role single- handedly but with a potential synergistic effects in co-infections. BRoV detection rate was significantly higher during colder months (77.9%), whereas no clear seasonal patterns were observed for BCoV and BNoV. The study revealed intensive management systems as a significant risk factor for BRoV infection. These findings expound the complexity of viral enteric diseases in calves and emphasize the need for specific management and control strategies. Further investigations are recommended to examine the interactions of viruses, genetic variations, and potential zoonotic risk of these viruses.