Strangles

Strangles is a disease caused by the bacterium Streptococcus equi.

The signs of a strangles infection can include a nasal discharge, cough, difficulty swallowing, poor appetite, swellings around the head and neck and a high temperature.

Young horses are more susceptible but horses of any age can be affected. Complications are rare and in 95% of cases the infection is confined to the head and neck, however in a small number of horses the infection may spread to other body organs and form abscesses, this is known as "bastard strangles". Rarer still is Purpura Haemorrhagica in which blood vessels themselves become affected and can spontaeneously bleed. Both these complications can be fatal.

A proportion of affected horses will become carriers of the disease and may not show any clinical signs but can act as a reservoir of infection for other horses.

DIAGNOSIS

To diagnose strangles in a horse showing signs of infection your vet will normally take a nasopharyngeal swab; an absorbent piece of cotton passed up the nose to sample the back of the throat. This swab can then be tested for presence of S. equi by culturing the bacteria or by testing for the presence of bacterial DNA.

After a possible infection a minimum of 30 days since cessation of the signs is the recommended time to test for carriers. Without testing for carriers after an outbreak it is impossible to say whether a horse or the horses in contact are possible sources of infection. Horses that have been in contact with an affected horse or a carrier horse may themselves become carriers.

The guidelines for testing horses for potential carriers are based on guidelines produced by the Animal Health Trust and the Horserace Betting Levy Board.

To test for carriers a series of three nasopharyngeal swabs need to be collected at 5-7 day intervals over the course of two weeks. If any of the three swabs tests positive for infection then it is recommended that the horse has an endoscopic examination of the guttural pouches. An alternative to three nasopharyngeal swabs is a single endoscopic examination and wash of the guttural pouches.

There is also a blood test that will show if your horse is infected with S. equi.

TREATMENT

Strangles can be treated easily with antibiotics, the usual choice being Penicillin. Antibiotics are usually only used if the clinical signs are severe enough to warrant it as most horses will recover without treatment. There is no current vaccine for strangles in the UK.

CONTROL

Strict biosecurity is essential in the control of strangles; all new horses entering a yard should be closely monitored and any horse that develops a nasal discharge should be isolated and tested.

Infection is spread by close contact between infected and uninfected animals including contact via feed buckets, water troughs, tack etc. The organism can live for long periods particularly in water.