Strangles is a respiratory infection of horses, donkeys and ponies caused by Streptococcus equi. It is a highly contagious disease and the most common bacterial infection of horses.
The major reason for its concern is the speed with which strangles spreads among horses, especially in a stable setting. In large horse populations, established outbreaks may last for months.
Moreover, some “recovered” horses (carriers) can harbour Strep. Equi in the guttural pouches with no outward clinical signs. Consequently, new or recurrent outbreaks are likely unless further diagnostic procedures, treatment and aggressive quarantine measures are used.
With onset, the horse appears depressed, dull, and stops eating. Typically, the temperature rises to 41°C. After a few days lymph nodes around the throat swell, forming abscesses. The horse can have difficulty breathing and swallowing (hence the name ‘strangles’). A nasal discharge is at first clear and then becomes purulent (thick with signs of pus), after the abscesses have ruptured in the nasal passages .Sometimes the abscesses rupture through the skin. The veterinarian surgically opens the abscesses to help breathing. Abscesses that rupture shed highly infective pus into the environment, which can infect other horses. In some outbreaks and in a small percentage of cases, these abscesses spread to other parts of the body (a condition known as ‘bastard’ strangles) which is very difficult to treat.
Fever, depression, loss of appetite, nasal discharge, and swollen lymph nodes make clinical diagnosis generally straightforward. Isolation of Streptococcus equi using swabs taken from the nasopharynx (in some cases including obtaining samples from the guttural pouch) and from abscesses confirms the clinical diagnosis. A blood sample can also be taken 2 weeks apart to identify previously infected horses and potentially infected horses in a quick non invasive manner.
Once inside a stable or yard, strangles can spread quickly through direct contact between horses or via indirect contact, e.g
tack and equipment
shared drinking bowls and feed
The bacterium is discharged (shed) from draining abscesses and the nose and it may survive in the environment, particularly water troughs. Once transmitted, signs of disease usually occur after 3-14 days, with abscesses formed up to 2 weeks following infection.
Isolation and Hygiene
Since strict hygiene procedures are essential to minimise the spread of infection. These notes provide general guidance on isolation procedures. Where any of these steps are not possible a suitable alternative should be agreed with your veterinary surgeon.
Isolate those horses suspected or confirmed of having strangles.
A separate water supply must be available for the isolated horses.
Separate equipment and utensils used for feeding, watering, grooming and cleansing must be used for horses in isolation. These must not be used on other horses unless they are first thoroughly cleaned and then decontaminated with an approved disinfectant.
As few people as possible should come into contact with the isolated horses and appropriate measures. This includes pet dogs and cats living at or visiting the yard.
Preferably attendants of the isolated horses should have no contact with any other horses during the isolation period. Where other contact is unavoidable, it should be kept to a minimum and only after thorough washing and disinfection of hands and a change or thorough disinfection of clothing including boots and impervious outer clothing.
If staff cannot avoid handling both infected and uninfected animals then, in addition to the disinfection and clothing changes mentioned, they should attend to uninfected animals first and only then deal with the exposed horses before finally attending to infected animals ideally as their last task on the yard.
Used bedding, uneaten food and water must be disposed of carefully. Bedding and uneaten food should be carefully disposed of (such as on a muck heap >30 metres away from grazing/exercise areas) and water should be discharged to the sewer or septic tank to avoid cross contamination.
After use, all movable equipment and utensils for feeding, grooming and cleansing within the isolation facility must be disinfected using a suitable disinfectant. (This can be supplied by your veterinary surgeon).
Good hygiene is essential for controlling the disease. There is no one treatment plan that is suitable for every case of strangles. Treatment often revolves around supportive care, good stable management and hygiene, assessing the use of antibiotics is best left to the attending vet.
After the lymph nodes swell and abscesses form, many vets advise only symptomatic therapy (warm packs to help the abscesses mature and possibly surgical opening). Subsequently, vets can recommend a washing (lavage) of the abscess cavity or cavities with antiseptic solution until healed, often weeks after first signs of the disease.