Detection of airborne bovine coronavirus RNA in pen environments and exhaled breath of calves.

Bovine respiratory disease (BRD) is a significant economic and welfare concern in the cattle industry. Commingling (mixing) events create environments conducive to the spread of bovine coronavirus (BCV), a common calf BRD pathogen. Although BCV is thought to spread primarily through direct contact, the role of airborne transmission remains unclear. This study aimed to investigate the potential for airborne and fomite transmission of BCV among weaned (8-10 wk old) Angus × Holstein calves during a controlled commingling event. Eighty animals across 2 cohorts, raised under commercial farming conditions at 7 source farms, were enrolled in the study. Air, exhaled breath, and surface swabs were collected from solid-sided pens housing BCV-shedding calves and an adjacent, unoccupied separator pen. Exhaled breath was sampled using a novel device (IMADGENN) designed to capture particles at defined distances from the source. IMADGENN is a purpose-built chamber equipped with HEPA-filtered air supply and extraction systems to ensure low background aerosol levels and efficient sample collection. A low amount of BCV RNA was detected in the air of both occupied and unoccupied pens (at least 2.5 m away from the closest shedding animal), and surfaces in unoccupied pens were also found to be contaminated. Bovine coronavirus was also detected in exhaled breath of shedding calves, at a distance of at least 1.2 m from the sampled animal. In conclusion, our findings demonstrate that BCV particles are shed into the environment via exhaled breath, resulting in contamination of air and surfaces with viral RNA. These findings suggest that airborne dispersal and fomites may be a potential transmission route for virions and could contribute to BCV spread during commingling events.