Cryptosporidium parvum and bovine coronavirus in naturally and experimentally exposed calves: clinical outcome and pathogen shedding

A comparative infection study was performed to investigate the clinical outcome and pathogen shedding patterns in calves experimentally infected with Cryptosporidium parvum and/or bovine coronavirus (BCoV). A total of 15 calves were enrolled and assigned into three infection groups (each n = 5) within 12 h of birth. Group 1 (G1) was experimentally infected with C. parvum, group 2 (G2) was experimentally infected with C. parvum and BCoV, and group 3 (G3) was experimentally infected with BCoV. Clinical outcomes were registered, and feces and nasal swabs were collected daily for 28 days. Prior to experimental infection, all calves were found negative for BCoV RNA in fecal and upper respiratory samples, but 12/15 calves had detectable C. parvum DNA in feces, meaning all groups were already naturally infected with C. parvum. Calves double infected with C. parvum (G1 and G2; experimentally and naturally infected) showed more clinical signs over a longer period of time, compared with calves experimentally infected with BCoV and also naturally infected with C. parvum (G3). The shedding pattern of Cryptosporidium DNA in feces was similar in all groups. The peak shedding period of C. parvum correlated with the days when calves displayed the most clinical signs. However, a significant increase in fecal BCoV RNA occurred after the period where calves displayed the most clinical signs. In this study, a double infection of neonatal calves with C. parvum (G1 and G2) resulted in a more severe clinical outcome than a mixed infection with C. parvum and BCoV.