What is strangles?

Strangles is an infection caused by bacteria called Streptococcus equi. It is highly contagious and the infection can be spread by horse-to-horse contact or by humans, tack, drinking troughs and other items in the horse’s environment.

What should I look for?

The characteristic signs include sudden onset of fever (high temperature) and loss of appetite. The horse may have difficulty swallowing. This is followed by swelling of the lymph nodes (glands) under the jaw and in the throat and the horse may hold his head low with its nose poked forwards to relieve discomfort and to aid respiration. There is usually a thin watery nasal discharge which soon becomes thick and yellow. One or more abscesses form in the inflamed lymph nodes. These tend to rupture either to the outside via the skin or into the back of the throat and discharge thick yellow pus. Horses usually recover fully after natural rupture of the abscesses. However, if you suspect strangles you should seek veterinary help without delay. Your veterinarian will help confirm the diagnosis by clinical examination and the collection of swab samples for laboratory investigation and will help you with appropriate treatment and management.

Which horses can become affected?

Strangles can occur in horses of any age but younger horses are more likely to become infected. After infection, most horses are immune to re-infection for several years. Old or debilitated horses are at increased risk of infection or re-infection.

Can stranges be treated?

Recommended treatments of strangles include application of hot towels to the swollen glands to encourage abscesses to burst or to grow to a size and maturity that allows them to be safely and successfully lanced. Once open, the abscess cavity should be flushed with saline or dilute antiseptic solutions and allowed to heal naturally.

The bacteria which causes strangles can be killed by certain antibiotics including penicillin, but there is considerable disagreement as to if or when antibiotic treatment should be given. The problem is that when abscesses form, they produce a dense fibrous outer capsule, which means that the antibiotics circulating in the bloodstream have difficulty in reaching and killing the infecting organisms. Therefore, if the antibiotics are stopped prematurely (i.e. before approximately 6 weeks) the bacteria can proliferate again and the abscess will grow once more. Consequently, some clinicians who have experience of strangles prefer to let the disease take its natural course. However, some horses with strangles develop such large abscesses at the back of the throat that they are in danger of suffocation, and then intensive antibiotic and anti-inflammatory treatment is essential. On occasions, these horses may also need ot have a tracheostomy (hole cut in the windpipe) performed.

In outbreaks of strangles, the temperature of in-contact horses should be taken daily and horses can be treated with a course of antibiotics from the very first sign of infection (i.e. rise in temperature), before abscesses start developing. This may prevent the disease from becoming manifest, but may also prevent horses from producing useful immunity so that they can become infected again later.

Can strangles be prevented?

It is most important to understand the highly infectious nature of this organism and do all that can be done to isolate cases and to prevent further spread to other horses, both on and off the immediate premises. We will help you set up a management protocol appropriate to your own location and circumstances.

Vaccines against strangles are available in Australia, but are not 100% effective. However, use of vaccines on horse establishments can decrease the number of horses affected and the severity of disease in outbreak situations. An initial course of 3 vaccinations 2 weeks apart should be given and then yearly boosters.  Prevention of the disease or its spread also depends upon good management. New horses should be isolated for 2-3 weeks and their temperatures checked regularly. Any horse which shows suspicious signs of illness (high temperature, nasal discharge, difficulty in swallowing, swollen throat or glands) should be isolated until strangles is confirmed or ruled out by veterinary examinations and laboratory investigations. Any horse which has strangles should be immediately isolated from all other horses. It should have its own water and feed mangers, grooming kit and tack and no equipment used for the affected horse should be allowed near other horses. One person should look after the affected horse(s) and avoid contact with all other horses. All equipment, stables, fences, floats, etc. should be thoroughly disinfected using a phenolic disinfectant.

Unfortunately, some horses become carriers of Streptococcus equi, most commonly in their guttural pouches, and can infect horses intermittently although showing no signs of infection themselves. This is probably the most important cause of infection recurring at intervals of several months, after apparent clearance from a herd. Thus some vets recommend collection of a deep nasopharyngeal swab and/or guttural pouch wash samples for laboratory investi-gations of horses having recovered from the infection.

Are there other or long term complications of the strangles?

Strangles can take an unusual course with abscesses forming deep in the body. This is often termed ‘bastard strangles’ and can be difficult to treat successfully. Affected horses may show signs of colic or abscesses might form in many internal sites. Cases lose weight and may require euthanasia on humane grounds due to colic, respiratory distress or other complicating illnesses associated with multifocal organ damage. If these cases are to be treated successfully, these horses require long term antibiotic therapy (weeks-months) and nursery care.

Carrier horses often only spread the infection when they are stressed e.g. at the time of foaling or after transportation or handling for farriery or routine worming or vaccination. Some carriers can be successfully treated by installation of medication into the guttural pouches. However, it is often difficult to know how these animals are best managed as they may be a risk of infection to other horses if not completely cured. This should be discussed with us.

Strangles is rarely fatal, but deaths can occur. Occasionally a horse which recovers from strangles will develop a condition known as purpura haemorrhagica. This is due to an unusual immune reaction to the streptococcal bacteria and results in widespread damage to blood vessels, resulting in swellings of the legs and head and bruise-like patches in the mouth. Your veterinarian should be called immediately if you suspect this life-threatening condition.







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