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Highly Contagious Horse Disease Breaks Out

Watch your horses carefully for signs of strangles, a highly contagious disease, warns Carrie Hammer, North Dakota State University Extension equine specialist.

"Many cases of the disease have been reported this year, with reports occurring in various locations throughout the Red River Valley," she says.

Strangles, also known as horse distemper, is caused by the bacteria Streptococcus equi, which infects the upper respiratory tract of equine species (horses, mules, zebras). The disease gets its name from the swelling of the lymph nodes under the chin and around the throatlatch area, which can interfere with a horse's ability to breathe.

Strangles can occur in any age horse, although horses between ages 1 and 5 are affected more frequently. The disease is highly contagious, with 50% or more of exposed animals becoming sick. However, the disease is rarely fatal (less than 5% in well-managed cases).

Initial symptoms may include depression, failure to eat or drink, clear nasal discharge that will get thicker and creamy as the disease progresses, fever as high as 106 F and swelling of the lymph nodes under the jowl or in the throatlatch area. Affected horses may stand with their necks stretched out and be reluctant to swallow. As the disease progresses, abscesses may develop in the swollen lymph nodes. In many cases, this is the first thing owners notice. As the abscesses mature, they will rupture and drain thick, cheesy material.

Horses become infected after inhaling or ingesting the bacteria. Usually this results from direct contact with infected animals, or through shared feed and water containers. Discharge from the nose or abscesses carries large concentrations of the bacteria and is highly infective. Contaminated clothing, boots, brushes and tack can spread the disease from one area to another.

Animals in the initial stage of infection and those recovering from the disease are the usual source of infection in other animals. In rare instances, chronic carriers can shed the bacteria for as long as six weeks after being infected even though they show no signs of infection.

Because strangles is highly contagious, affected horses should be isolated immediately, Hammer says. A variety of treatment options are available, and treatment choice depends on veterinarian preference and the stage of the disease. Streptococcus equi is very sensitive to a variety of antimicrobials, with procaine penicillin G the drug of choice. Mild cases usually resolve themselves without incident and probably do not require antibiotic therapy.

Applying hot packs to swollen and abscessed lymph nodes can be beneficial. In some cases, abscesses may need to be lanced to facilitate drainage and healing.

Any equipment that has come in contact with an affected horse, including brushes, buckets and tack, should be disinfected thoroughly. Streptococcus equi is sensitive to most disinfectants as long as label directions are followed and the product is used appropriately.

Hammer says that in an ideal situation, personnel who take care of infected horses should not be the same people who care for other animals on the premises. If this is not possible, workers should deal with affected horses last. People caring for sick animals should wash their hands thoroughly and change their clothing and boots before leaving the isolation area.

Most horses will develop immunity to strangles after infection. That immunity lasts at least five years in most animals. However, immunity to the disease will decrease through time, so animals may become reinfected.

Several strangles vaccines are available. Vaccination will not guarantee prevention of the disease, but it may lessen the severity and duration, and does seem to be effective in helping control outbreaks, Hammer says.

Owners should call their local veterinarian if they have questions about strangles.

Source: NDSU Extension Communications

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