The International Society for Infectious Diseases (ISID) and Nicole Kraft of the the United States Trotting Association have issued a bulletin on an outbreak of the highly-contagious horse disease known as “strangles” at Northfield Park near Cleveland, Ohio. Strangles is the symptomatic name given to horses infected with the bacteria Streptococcus equi.

The initial outbreak affected horses in six different barns at the filled-to-capacity stable area, making quarantine difficult.

The attending veterinarian, Dr. Dan Wilson. took immediate steps to quarantine the affected horses in their stalls and instituted biohazard procedures that included sterile shoe and body coverings, and disinfectant washes for those who handle the horses.

Ohio State University responded to the emergency by dispatching, at no charge, Dr Phoebe Smith, a recent arrival from California with expertise in treating large-scale strangles outbreaks, who commented “With a case like this, in a high-density population, we are most concerned with biosecurity and containment. It’s actually not an extreme number of horses affected, so in that sense it was not as bad as it could be. But they do have many horses co-mingled and a fair amount of traffic — horses arriving and leaving. They very appropriately recognized that the potential is really bad.”

Legally, the track cannot contain the horses stabled there. A horse sale held yesterday announced that it was withdrawing all horses from Northfield Park.

The racetrack’s management agreed to pay half the cost of diagnostic tests for horses at the track.

Barring further outbreaks, the track should be “clean” in late March.

In horses, strangles causes swollen lymph nodes and a nasal discharge that may resemble pus. The lymph nodes may swell and burst, thus spreading more bacteria. The horse may be lethargic and anorectic.

The disease is spread through objects such as water troughs, feed buckets, brushes, reins, and other equipment if contaminated with infected pus. Recovered horses can spread the disease for up to 8 to 10 months even though they can appear clinically healthy and normal. Researchers in Great Britain are investigating the role that asymptomatic carrier horses play in spreading the disease.

Strangles research was the beneficiary of a personal Christmas donation from Queen Elizabeth of England in 2007.

Thanks to HarnessLink, the USTA, and ISID for help with this blog post.