What horses are at risk for contracting Strangles?

American Association of Equine Practitioners


Any age horse can be affected, but it is the very young and the very old who usually suffer the worst. Young horses may not have yet developed sufficient immunity through natural exposure in their short lives, while the immune system of the geriatric horse may be less functional due to age-related decline. It takes about 3-14 days for the disease to incubate once the horse has been exposed until he shows clinical signs of infection. Not all infected horses develop obvious symptoms of disease yet these asymptomatic individuals may serve as carriers and shed the organism through their respiratory secretions and saliva and spread it to other susceptible horses.

Strangles is a highly contagious disease, particularly in conditions of stress. This includes situations where horses are housed in crowded areas, or with poor hygiene, or with inadequate nutrition. Transmission occurs via direct contact with nasal secretions or saliva. Flies also spread the disease, as do contaminated feed buckets, rakes, human hands and clothing. The organism can survive in the environment for a couple of months, particularly if shielded from the sun inside of dark barns or within the soil. Once established on a property, another outbreak may occur on that farm a year or two later. The infection keeps cycling through horses to the environment and back to horses to become a persistent and frustrating management issue.

Once a horse has been infected with strangles, it is possible for him to continue to shed the organism through nasal secretions for months. Most horses stop shedding within about 6 weeks, but the potential exists for a previously sick horse to carry the infection to others despite appearing to be fully recovered. Nasopharyngeal swabs of suspected carriers or of previously infected horses can help identify those that may be shedding S. equi organisms yet are not exhibiting clinical signs. In one study, the average period of shedding from carriers was 9.2 months, with one horse shedding for as long as 42 months. Sixty-eight percent of horses continued to shed for at least four weeks following resolution of clinical signs. Seventy-five percent of horses infected by strangles develop a long-lived immunity once they recover from the disease.

Reprinted with permission from the American Association of Equine Practioners www.myhorsematters.com
2004-2012 Horse Tack Review

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