Detection of equine parapoxvirus in the stable environment during pastern dermatitis outbreak in Finland

Equine parapoxvirus (EqPPV) has emerged as a cause of recurring pastern dermatitis outbreaks in horses in Finland. First detected in 2013, EqPPV has since been associated with potentially hundreds of clinical cases and suspected zoonotic transmission. Based on serological data and field reports, EqPPV causes pastern dermatitis outbreaks in Finland every few years. This study aimed to investigate the environmental presence and plausible transmission dynamics of the virus to prepare for future outbreaks and give targeted guidelines to stable staff and veterinarians.

After a large-scale EqPPV outbreak affecting hundreds of horses occurred in Finland in winter 2021-2022, PCR diagnostics was carried out whenever EqPPV was suspected to monitor the situation (25 trotting horses from 20 stables between April 2022 and May 2025). Following a period with no detected EqPPV cases from April 2022 to January 2025, a new outbreak occurred in early 2025. Between February and May 2025, the majority of Finnish trotting stables (8/10) submitting diagnostic equine samples, tested positive for EqPPV DNA. Environmental samples (n = 161) were collected from six case stables and two control stables from various surfaces in direct or indirect contact with horses. EqPPV DNA was detected on grooming tools, stall infrastructure, bedding, materials handled by humans, and hands of humans, suggesting multiple possible indirect transmission routes and large-scale spread of EqPPV DNA in infected stables. Notably, 83.3% (5/6) of the tested case stables had EqPPV PCR-positive environmental samples and 17.4% (24/138) of all environmental samples tested positive.

This study confirms a recent EqPPV outbreak in Finnish trotting stables and demonstrates the presence of EqPPV DNA in clinically affected horses and the stable environment, e.g. common spaces and shared equipment. Detection of EqPPV DNA on common equipment and spaces, and on personnel shows a widespread environmental distribution during the outbreak. Overall, these findings underscore the high potential for reoccurring outbreaks and the importance of continued surveillance and early implementation of hygiene and preventative practices to minimize the effect of future outbreaks.