A study in Australia has found no evidence that the vaccination against the deadly Hendra virus affects the racing performance of thoroughbreds.
The work of University of Sydney researcher Kathrin Schemann and her colleagues involved analysis of data from horses competing at six south-eastern Queensland racetracks.
They began by looking at 4208 race starts by 755 horses. For each horse, they focused on a six-month racing window, covering three months before and three months after they received their initial shot of the Equivac HeV Hendra virus vaccine.
The researchers, writing in the Australian Veterinary Journal, said they found no significant difference in performance before and after the initial Hendra vaccination based on a range of parameters – Timeform rating performance data, the margin to winner, prize money, wins, or placings.
Since 1948, Timeform ratings have been an internationally recognised standard for the global measurement of thoroughbred racetrack performance.
Further analysis of Timeform ratings for a further 7844 race starts by 928 horses failed to identify any significant change in rating trends relating to second and subsequent Hendra vaccinations, or any evidence of a cumulative effect for the number of vaccines received.
The authors, discussing their findings, said their aim was to assess any potential adverse effects of the vaccination on horse performance. They found none for the variables examined in the study.
“Immune-related adverse reactions to vaccinations are more likely to occur with doses subsequent to the primary dose. By comparing the performance before and after two or more vaccinations in the same horse, this study also found no evidence of a cumulative effect on racing performance of multiple vaccinations.”
They said their findings had important implications for horse owners, trainers, the Australian horse industry and its regulators, equine veterinarians and government animal health authorities.
“The most frequently given reasons for non-adoption of Hendra vaccination by some horse owners and horse associations have been concerns about the potential for adverse reactions and effects on performance caused by vaccination.
“The findings of this research provide evidence to diminish concerns regarding the Hendra vaccine’s safety and specifically its potential effect on horse performance.
“Equine veterinarians may use these results to provide evidence-based recommendations regarding preventive horse healthcare and allow horse owners to make informed decisions regarding Hendra vaccination.”
Similarly, the information can be used to guide policy decision-making on Hendra vaccination.
The authors said the Hendra vaccine for horses had proved controversial for a variety of reasons, including the way the vaccine was brought to market, workplace health and safety considerations for veterinarians, delays in vaccine exclusion testing, and implications for equine export and insurance. It was initially released under a Minor Use Permit.
“Despite the sound reasoning behind the vaccine’s unconventional release, early views held by some horse owners were that the vaccine was unsafe and insufficiently tested.
“All facets of the safety, efficacy and adverse reaction reporting process were reviewed by the Queensland Parliamentary Inquiry in 2016, with the vaccine being verified to be safe and effective.”
They said the regulatory requirement for veterinary-only administration of the vaccine resulted in mistrust of private veterinarians, who were perceived by some in the horse industry to be motivated only by a vested financial interest.
“The absence of scientific evidence regarding the effects of Hendra vaccination on horse performance may have contributed to inconsistent veterinary advice to horse owners and trainers, further contributing to the uncertainty regarding the safety of the vaccine.”
Uptake of the Equivac vaccine is considered moderate to date, with more than 550,000 doses having been given to about 140,000 horses Australia-wide.
The total number of horses in Australia is unknown. However, domestic horse numbers were estimated at just under 1 million in 2007, suggesting a vaccination uptake of about 14%.
The researchers said their study had delivered critical, unbiased scientific information that would aid horse owners in making informed decisions regarding vaccination of their horses.
The president of the Australian Veterinary Association’s equine group, Dr Ben Poole, said the study, funded by the Queensland Racing Integrity Commission, would hopefully reassure those involved in racing that the vaccine was safe, had no negative effects on racing performance, and was the best way to help prevent deadly Hendra infections in horses and people.
“We echo Commissioner Ross Barnett’s concern regarding the number of horses that have not been vaccinated against Hendra virus and the potential effect on horse welfare that not vaccinating can have on racing horses.
“Precautions must be taken by horse owners, handlers and veterinary staff to minimise the risk of Hendra virus infection in horses and people,” Poole said.
“Vaccination of horses against Hendra virus is the cornerstone of these precautions.”
Based on the findings, people in the industry could be confident that vaccinating brought health and welfare benefits to the racing community, he said.
“It should dispel rumours that vaccination affects performance,” Dr Poole said.
The Queensland Racing Integrity Commission recently announced that owners will be given the option to receive the first Hendra vaccination free, to encourage a greater uptake.
“We applaud the commission for the action they’re taking to protect the community from Hendra and we encourage other industry bodies to follow the example,” Poole said.
The Australian Veterinary Association recommends that all horses in regions known to, or likely to have Hendra virus spillover events, be vaccinated against the disease. If horse owners are unsure about the recommendation in their area, they should consult their veterinarian.
The Hendra virus is carried by Australian fruit bats. Horses can pick up the infection, most likely from contact with infected flying fox urine or other fluids such as mucus.
Infected horses are further able to transmit the virus to other horses, dogs and humans, acting as an amplification host for the virus.
To date there have been 102 horse deaths caused by Hendra infection, resulting in 19 human exposures.
Seven human cases of infection have occurred, four of whom have died, giving a human case fatality rate of 57%.
There are no approved therapeutics available for human use, although monoclonal antibody therapy has been offered as post-exposure therapy on compassionate grounds to 13 people following natural exposure to infected horses and a further two people following exposures in a laboratory setting.
For a localised Hendra outbreak, the average response cost and the economic loss due to horse deaths are estimated at $A30,660 per horse.
Schemann, K., Annand, E., Reid, P., Lenz, M., Thomson, P. and Dhand, N. (2018), Investigation of the effect of Equivac® HeV Hendra virus vaccination on Thoroughbred racing performance. Aust Vet J. doi:10.1111/avj.12679