The ability of horse shows to act as a springboard for the spread of contagious diseases has long been recognised.
One of the highest profile examples was in Australia, where the equine flu virus most likely carried by a Japanese thoroughbred escaped from the Eastern Creek Quarantine Centre near Sydney in August, 2007.
It somehow reached a three-day horse event at Maitland, New South Wales. The disease was then spread across a huge area, as far north as Queensland, when competing horses were taken home.
Australian horses, never before exposed to the virus, were infected in their thousands, with the successful containment effort costing $A100 million. A further $A261 million was spent in government assistance to the horse industry.
Now, researchers in Ontario, Canada, have dissected a local horse show to learn more about the networks that exist within the horse community to determine how they may influence potential disease transmission.
Their findings, reported in the journal BMC Veterinary Research, provide insights into not only the horses at the show, but the network of potential contacts associated with an equestrian show.
University of Guelph researchers Kelsey Spence, Terri O’Sullivan, Zvonimir Poljak and Amy Greer said that identifying the contact structure within a population of horses attending a competition was important in understanding the potential for the spread of equine pathogens as the horses moved from location to location.
The study team focused on a two-day silver level dressage competition in southern Ontario on July 6 and 7, 2014.
Horse show participants completed a questionnaire about their horse, travel patterns, and infection control practices. Responses were received from horse owners of 55 of the 69 horses attending – a 79.7% success rate.
Sixty-nine percent of participants said there were other horses from their home facility at the same show.
The home facilities of 55% of participants were less than 50 km away from the show location, although at least one participant had travelled 370km to attend.
Most participants – 80% – came from home facilities that housed horses owned by four or more owners. The average number of horses boarded at individual home facilities was 22.
The 69 horses came from 38 properties in all. Analysis of the data showed wider contact with a total of 779 horses, most of whom lived at the competing horses’ home properties.
Owner-reported vaccine coverage levels in the preceeding 12 months for horses at the show included equine influenza virus (96%, 50/52), rabies (90%, 47/52), strangles (60%, 31/52), West Nile virus (88%, 46/52), eastern equine encephalitis and western equine encephalitis (85%, 44/52), equine herpesvirus (73%, 38/52), and tetanus (83%, 43/52).
Only one participant stated that their horse was unvaccinated for all diseases listed, while 7% (4/54) were unsure of the vaccination status of their horse.
The owner-reported vaccine coverage level in the study was much higher than previously reported for Ontario horses, they noted.
It was possible, they said, that the horses in the current study may be have been highly vaccinated due to their frequent participation in equestrian events.
Owners in the study also demonstrated high compliance with most infection control practices, in particular by reducing opportunities for direct and indirect contact while away from home.
“The inclusion of the secondary contacts in the network demonstrated the high amount of connectivity beyond the horses that were present at the show, highlighting the importance of describing these contacts when estimating the risk of disease spread in the population,” Greer and her colleagues said.
“Simply planning disease intervention strategies based on the horses that attended the show without explicit consideration of secondary contacts would severely underestimate the resources required to control a potential outbreak.”
Two horses in the study were found to have had contact with horses in three locations, indicating that they were the most important horses for potential disease spread in the network.
The authors said the results of the study provided information that could be used by equestrian show organizers to configure event management in such a way that can limit the extent of potential disease spread.
Descriptive and network analyses of the equine contact network at an equestrian show in Ontario, Canada and implications for disease spread
Kelsey L. Spence, Terri L. O’Sullivan, Zvonimir Poljak and Amy L. Greer
BMC Veterinary Research 2017 13:191 DOI: 10.1186/s12917-017-1103-7