One in 10 horses in the United States with acute upper respiratory tract infections tested positive for equine influenza in a study, researchers report.
The research was based on the testing of nasal-secretion samples taken by veterinarians across 239 practices during a 45-month period from 2010 to 2013. The vets, located across 38 states, submitted samples from 2605 equids in all.
A diagnosis of equine influenza was made based on the presence of clinical signs – fever, lethargy, nasal discharge and coughing – and a positive laboratory result for the virus using a quantitative polymerase chain reaction test.
A total of 230 equids – that’s 9.7 percent – tested positive for the virus.
A higher-than-expected proportion of positive test results occurred among horses in the 1–5, 6–10, and 11–15 age groups when compared to those aged under a year.
Fever, nasal discharge and coughing were the most common symptoms associated with positive horses.
Of the 230 positive cases, 107 were quarter horses, 20 were thoroughbreds, 19 were warmbloods, 16 were American paint horses, 15 were ponies, 12 were Arabians, 4 were standardbreds, 4 were draft horses, 20 were other assorted breeds, and for 13 the breed was not reported. There were 89 mares or fillies, 20 stallions or colts, 105 geldings, and 16 animals with no sex noted.
The researchers, whose findings have been published in the Journal of Veterinary Internal Medicine, compared their results with previous flu data obtained between March 2008 and February 2010.
Horses that tested positive in the latest research were significantly older and more of them were found to be vaccinated against equine flu when compared to positive animals from the 2008-2010 study period.
The researchers, from the University of California and Merck Animal Health, said the results underscored that older and previously vaccinated horses were susceptible to equine flu.
Epidemiologist Dr Nicola Pusterla and his colleagues said their findings were in agreement with the World Organisation for Animal Health’s expert surveillance panel on equine flu, with questions around the effectiveness of the flu vaccines available in the United States.
“The suboptimal protection of vaccines commercially available in the United States also is supported by the observation that significantly more horses in the … positive group had been vaccinated in the time period [of] less than 6 months when compared to the time period 6–12 months and more than 12 months.
“Information pertaining to vaccine brand and manufacturer was unavailable for the study horses, and thus no conclusions can be drawn regarding the efficacy of specific vaccines.”
They said commercial killed and inactivated equine flu vaccines should contain epidemiologically relevant viruses and should be updated in a timely manner to confer optimal protection.
Equine flu virus is considered one of the leading causes of infectious respiratory diseases in equids worldwide and has severe financial implications for the horse industry.
“The global transportation of horses has been responsible for numerous outbreaks of equine flu by introduction of the virus into previously unexposed horse populations,” they wrote.
“Adherence to strict quarantine and vaccination protocols and vigilant monitoring are required to avoid the introduction and spread of equine influenza virus among all horse populations.”
Pusterla, N., Kass, P.H., Mapes, S., Wademan, C., Akana, N., Barnett, C., MacKenzie, C. and Vaala, W. (2015), Voluntary Surveillance Program for Equine Influenza Virus in the United States from 2010 to 2013. Journal of Veterinary Internal Medicine, 29: 417–422. doi: 10.1111/jvim.12519
The full study can be read here.