Equine Influenza in the U.K.

Equine influenza has been confirmed to date in 14 Thoroughbred race training stables since March 13, according to the United Kingdom’s Animal Health Trust in Newmarket, Suffolk.

Influenza is not usually life threatening, but rather makes a horse uncomfortable and vulnerable to other diseases. Treatment typically includes a minimum of three to four weeks of rest to avoid long-term respiratory problems. Affected horses spread the virus via aerosol droplets or fomites (any objects capable of mechanically transporting an infectious agent). Horses exposed to transient populations, those stressed by shipping or heavy training schedules, youngsters, and seniors are most at risk of contracting influenza.

Clinical signs in the current outbreak have rapidly spread throughout affected premises. “Signs (in vaccinated animals) have been relatively mild compared to infections among non-vaccinated horses,” said an announcement from the AHT. “Signs in the current outbreak have included acute coughing, mainly at exercise, with some horses developing a nasal discharge. Fever has been seen but is not a consistent sign. An unusual feature of the current outbreaks is that, in most affected yards, the first horses to develop disease have been 3-year-olds or older horses.”

The Animal Health Trust has been completing detailed epidemiological and virological investigations of the outbreak with the help of area veterinarians. Information gleaned from these investigations is vital to ensure that any strain variation is monitored and allowed for in future vaccine updates. The virus isolated from the earliest cases is closely related to a virus that was isolated in Lexington, Ky., in the autumn of 2002. Scientists at the Animal Health Trust are trying to figure out why the disease has been seen in vaccinated racehorses, so they can make recommendations for improving vaccination protection in the future.

Scientists at the AHT are working closely with vaccine manufacturers and human influenza experts to better understand the virus more quickly. In the meantime, they are advising trainers in the U.K. to consider a re-vaccination (booster) program, in consultation with their own veterinarians. Antibody levels decline steadily following vaccination, and veterinarians anticipate that boosters will increase the level of immunity, even though they cannot guarantee full protection.

In light of the findings thus far, the AHT, the National Trainers’ Federation, and the British Jockey Club, have issued the following advice to U.K. racehorse trainers and horse owners.

  • Trainers are advised to increase observation and recording of signs of respiratory disease. This includes taking and recording of rectal temperatures and nasal discharges from all horses twice daily. Coughs should be counted by all riders for each horse during exercise and recorded.
  • Where signs of influenza infection are suspected, particularly among older horses, trainers should consult their veterinarians immediately.
  • Veterinarians suspicious of influenza infection are advised to take nasopharyngeal swabs and serum blood samples from a representative samples of acutely infected horses and horses housed in close proximity to those who are not yet showing signs. Experience in this and other outbreaks indicates that a positive diagnosis may be made more easily in horses incubating the infection.
  • Vaccination will increase the overall level of immunity in a yard, although it is clear from the current outbreaks that re-vaccination will not guarantee protection from infection.
  • Although this may be difficult to practically achieve, trainers should take particular care with horses returning from racing at the present time. These horses should be kept as well isolated from the rest of the yard as possible and particular care taken to observe these horses for several days after returning home.
  • In yards where influenza has been diagnosed, affected horses should be rested and strenuous exercise avoided.
  • In accordance with the NTF Code of Practice for Respiratory Diseases, horses that may have been in contact with affected horses should not be sent racing.
  • As a general principle racecourse stable managers should try to ensure that horses from training centers are stabled together to minimize the risk of spreading infections between centers.
  • Particular attention should be paid to the cleaning and disinfection of the British Jockey Club Sampling Unit between horses.


About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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