Strangles is one of the most important equine diseases. It is a notifiable disease in Victoria under the Livestock Disease Control Act 1994. If your horse has Strangles you have a legal obligation to report it to the DPI within 7 days. If you suspect the disease is present please contact the hospital immediately for advice.
Strangles is a highly contagious infectious disease of the upper respiratory tract in horses. Caused by a bacterium called Streptococcus equi (S.equi), the disease affects horses, ponies and donkeys. Strangles is endemic and is easily recognised (see clinical signs). The disease tends to be more prevalent in the colder months and outbreaks may follow the introduction of new horses onto a property, or the mixing of groups of horses, at studs, shows or camps, or those on agistment properties with other horses. Horses of any age can become infected but strangles is generally more common in younger horses, whose clinical symptoms will be more severe.
The incubation period of the disease is usually about a week but it can be up to 3 weeks. Transmission is via both oral and nasal routes. Infection can also occur by direct contact between individual horses and/or through indirect contact through contaminated feed, water, bedding, stables, stable utensils and transport vehicles.
The S. equi bacteria is tough and can survive in pus and purulent discharges for many months and in nasal discharges for several weeks and for long periods in the environment. Bacterial shedding usually ends rapidly after clinical recovery and can be confirmed by negative culture of swabs from the back of the throat (nasopharyngeal swabs). Occasionally a horse will become a long-term carrier.
The classic signs of Strangles are usually visible within 3 to 8 days of an animal becoming infected and include:
- The rapid onset of a high temperature (39.5 to 40.5 C)
- Loss of appetite
- Discharge of yellow pus from the nose
- Symmetrically enlarged glands of the head and neck that often form abscesses
- Coughing and difficulty swallowing
A discharge of mucus from the nostrils is sometimes the only symptom seen. A carrier state without any obvious clinical signs is also possible. When abscesses burst a thick yellow pus is discharged. Abscesses rupture and drain within 2 weeks and drain and recovery is generally without incident. Symptoms can last for days or for months and, even after infected horses have recovered and appear healthy, affected horses will remain infectious for at least 4 weeks.
How is Strangles diagnosed?
We will confirm a suspected Strangles diagnosis by taking a swab from the back of the nasal cavity. Definitive diagnosis is based on a culture of S. equi, which may take several days to confirm a diagnosis, and a culture may fail to isolate S. equi if antibiotic treatment has already commenced.
Any suspected case of Strangles must be treated immediately to try to control infection. Each case is assessed and treated individually but the primary treatment in less severe cases is isolation and good nursing care to keep the horse comfortable and quiet until the abscesses burst and the horse acquires a natural immunity. We may prescribe non-steroidal anti-inflammatory medication to reduce a high temperature and/or to assist with painful swellings. Once abscesses have burst they are treated by washing the site with warm water and antiseptic.
Affected horses must be kept isolated for 6 to 8 weeks to prevent the spread of the disease. Good biosecurity and hygiene must be observed when handling infected horses.
Complications are uncommon, and most horses recover uneventfully but some horses will contract Bastard Strangles, where bacteria spread through the body and cause abscesses in the lungs, liver, spleen, kidneys, brain, and lymph nodes. These cases can be fatal.
Purpura Haemorrhagica – where red spots form on skin and mucous membranes, caused by bleeding from smaller blood vessels — is also possible and is generally fatal. In these cases swelling of the limbs and head will be present.
A small number of horses can develop Chronic Carrier Status. These animals carry Strangles in the guttural pouch — an out-pouching of the back of the throat — for months after they have recovered from the disease. Carrier horses appear healthy but will shed bacteria in nasal discharges and are a source of infection for other susceptible horses.
Infection can be controlled through the isolation of infected horses until they are free from infection. The spread of the disease can be limited by the early detection of shedders amongst newly-affected horses and their contacts by taking three nasopharyngeal swabs over a two week period and culturing the swabs for S. equi. In the majority of cases a series of 3 negative swabs provides strong evidence of freedom from infection.
All infected horses, and their in-contacts, need to be under veterinary supervision while in strict isolation, with the highest possible standards of hygiene. Horses should not enter an affected stud unless they are vaccinated and can be kept in strict isolation from all sources of infection.
A vaccine is available for Strangles. While vaccination will not always prevent disease in individual horses, it can assist control by reducing the spread of disease in an outbreak and limiting the severity and duration of the disease in individual animals. An initial course of 3 injections two weeks apart is given, followed by at least annual booster vaccinations. We strongly recommend that all horses, but particularly those travelling to shows, events or mixing with other horses, are vaccinated. Please call the hospital for further information.
Under the Livestock Disease Control Act 1994, a person must report Strangles if they know or have reason to suspect that strangles is present in horses or horse products. There is no regulatory action if strangles is detected on your property. Properties are not placed under quarantine, bio-security measures are put in place to prevent further spread.
Notification can be made by telephone to the District Veterinarian or Animal Health officer at your local Department of Primary Industries office or to the Disease Watch Hotline on 1800 675 888. Or you can call the hospital and we will advise the authorities.