The cause of "Strangles" is a bacterium called "Streptococcus equi", which is a wide spread disease of horses and donkeys, but is also found in a few horses not showing symptoms. All ages of horses can be infected by the disease which is commonest and most severe in young horses. The spread of the disease is usually horse to horse contact via nasal or abscess discharge, but can also be spread by discharge carried on clothing or inside lorries etc. The bacterium needs a moist environment to survive, so clothing and the environment do not act as sources for very long, unless they remain wet. Once established, this disease is often highly contagious.

The disease has an affinity for lymph tissue (e.g. tonsils and lymph nodes), but can also affect other structures, like joints when it is known as "Bastard Strangles". Usually symptoms involve a combination of the following signs after an incubation of 3-14 days of exposure.

• High temperature (normal is 100.5 - can be as high as 106)
• Depression, loss of appetite, difficulty swallowing, bad breath
• Swollen jaw and head, extension of the head and neck. Hard, painful lump under the middle of the jaw or below the ears. Reddened inside eyelid (conjunctivae).
• Nasal discharge - often very thick, profuse and custard-like.
• Coughing and/or "strangled" sound to respiration (this is the origin of the name"strangles", because in a few cases abscesses develop at the throat which can cut off the flow of air to the lungs by obstructing the larynx). As they develop abscesses usually ripen and burst in 7-14 days, often under the jaw, but also inside the throat. The discharge which bursts out is highly contagious. Symptoms may last from less than a week to over 2 months, but usually subside after 2 weeks. Some horses may relapse after a period of apparent recovery.

Complications

Unfortunately complications that arise from Strangles are not uncommon.

"Bastard strangles" is defined as any spread to joints, brain, lungs muscle, chest and abdomen or any area away from the lymph nodes of the head. If it does establish in one of these places in the body, the chances of a good outcome are greatly reduced.

"Purpura" (purpura haemorrhagica) - extreme depression with severe filling of the legs and head. Pin-prick bleeding onto the tongue and other mucous membranes is seen. Survival is as low as 50%.

"Anaemia" (autoimmune haemolytic anaemia) - this only rarely complicates strangles, and produces a very depressed horse with rapid self-destruction of red blood corpuscles - often will develop swollen skin at the base of the abdomen and filled legs. Usually a second high fever develops some time after the initial Strangles infection.

"Roaring" (left laryngeal paralysis) - may result from pressure caused to the nerves supplying the larynx. These horses make a 'noise' at exercise - it is generally permanent.

This is carried out by your vet, but may include investigating the bacterium to prove its identity as Strep Equi. The use of antibiotics such as penicillin may be considered and also drugs to lower high temperatures. Once abscesses burst they can be flushed with very diluted disinfectant solutions, if they are readily accessible e.g. below the jaw. Soft food may encourage a horse to swallow with more ease.PreventionThe control of spread can be difficult because by the time a horse develops the full set of symptoms it may have spread to other horses in the same yard by mild nasal discharge or coughing. Careful isolation of affected cases should involve:

• Separate tack, grooming kit, feet, buckets and stabling.
• Overalls worn inside the infected stable and taken off when you leave.
• Disinfectant placed at the door for washing feet and hands when you leave the box.
• Feeding the infected horses last, so you do not go to another horse after them.
• Burning contaminated bedding and disinfecting boxes one a horse vacates it.
• Horses may be swabbed to check for residual infection, but a negative swab does not prove the horse is clear.

The use of antibiotics in unaffected contact horses may be considered by your vet.

Immunity

A vaccine is available abroad, but not in the UK. 70% of infected horses develop a solid, enduring immunity, but it may take 6-8 weeks to develop after clinical signs first appear. Infected horses may shed the bacterium in their nasal discharges for 3-4 weeks after the disease starts. If the pasture has been grazed by infected horses, it may be prudent to rest if for a month before being grazed again.

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