Swollen lymph nodes are a symptom of strangles, a disease that often affects young horses.

From the American Association of Equine Practitioners, an AQHA educational marketing alliance partner

Strangles is caused by bacterial infection with Streptococcus equi subspecies equi (referred to as S. equi). The bacteria typically infect the upper airway and lymph nodes of the head and neck. The disease was first reported in 1251. The infection is highly contagious in horse populations, particularly affecting young horses, and can recur on farms with previous outbreaks of the disease.

It is one of the most commonly diagnosed contagious diseases of horses worldwide. The bacteria can survive on water troughs for more than a month, but the primary source of recurrent infections is most likely asymptomatic carrier horses that can shed the bacteria to other horses for months and years.

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Clinical Signs of Disease

Historically, strangles got its name because affected horses were sometimes suffocated from large, infected lymph nodes that obstructed the upper airway or trachea. The hallmark clinical signs of infection are fever (a temperature of greater than 101.5 F), nasal discharge and enlarged lymph nodes in the space between the lower jaw bones, which ultimately abscess.

Pus-filled nasal discharge is typically present, although it may initially be clear. The lymph nodes in the area behind the throat latch can also become enlarged and abscess.

The lymph nodes will sometime drain into the guttural pouches, which are air-filled spaces within the head that are an expansion of the Eustachian tubes.

Though strangles is highly contagious and can affect many horses on a farm, most horses with infection recover without complication. Complications from the infection include spread of the infection to lymph nodes other than the head and neck, immune-mediated disease, muscle disease and pain, and lack of milk production. Horses that develop a complicated infection typically require antibiotics and additional therapies based on veterinary examination.


Antibiotic therapy remains controversial for the treatment of strangles. Complicated cases generally require antibiotic and other supportive therapies.

There is some evidence that treatment with antibiotics (such as penicillin) at the first sign of fever and in horses with no lymph node enlargement might prevent infection. However, early antibiotic treatment will also prevent these cases from developing immunity to the infection and subsequently makes them susceptible to reinfection sooner.

Management of an Outbreak

The first and most important thing to remember in a suspected outbreak of strangles is to involve your vet right away to determine the diagnosis and the best control practices for your particular farm.

Strangles is a reportable disease in some states, and the state veterinarian might need to be notified as well. Movement of any horses on or off the farm should be stopped, and new horses should not be introduced. Take the temperature of all horses on the farm twice daily (normal rectal temperature is 99 to 101.5 F).

Monitoring the rectal temperature and isolating horses at the first sign of fever is one of the most effective ways to stop the spread of infection. Infected horses can transmit the bacteria to healthy horses one to two days after they develop a fever.

An isolated area should be set up for horses with fever and any other signs of illness. Extreme care should be taken not to mix infected or exposed horses to unexposed horses.

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Ideally, three groups of horses should be created:

    • Infected horses
    • Horses that have been exposed to or been in contact with infected horses
    • Clean horses with no exposure

Unexposed horses should be kept in a clean area and ideally should have separate caretakers, cleaning equipment, grooming equipment, water troughs and pasture. People and equipment can transfer the infection from horse to horse. Extreme care, hand washing and disinfection of supplies must be observed by everyone involved. If different individuals cannot care for infected and healthy horses, the healthy horses should always be handled first

Additional Preventive Measures

Here are some additional suggestions for reducing your risk:

    • Require a current health certificate for new horse arrivals on the farm.
    • Ask owners of new horses about a history of strangles and consider testing new horses to see if they are shedding the bacteria.
    • If feasible, quarantine new arrivals for two to three weeks and monitor their temperature.
    • All horses should have individual water buckets that are routinely disinfected.
    • When traveling to shows, minimize your horse’s exposure by bringing your own feed, buckets and equipment. Minimize use of shared stalls or pastures at show grounds.
    • If horses are pastured together, group them according to their age and risk level.