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What is Strangles?

Strangles is an infection caused by a bacterium called Streptococcus equi. It is highly contagious and the infection can be spread by horse-to-horse contact or by contact with environmental items such as contaminated humans, tack, drinking troughs or stable yard equipment.

What should I look for?

Signs can vary greatly to the extent that some horses may be very ill, whereas others simply show very minor signs or no signs at all. It should always be remembered however that a carrier state exists, where horses show no symptoms but still carry the disease.

The classic signs include being dull and off colour with a 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, in the throat and under the ear and the horse may hold his head low with his nose poked forwards to relieve discomfort and to aid breathing (hence the name ‘strangles’). There may be a nasal discharge which becomes thick and custard like. Abscesses may form in the enlarged lymph nodes which can rupture either to the outside, through the skin, or into the back of the throat and discharge thick creamy-yellowish pus.

Horses usually recover fully, in time, after natural rupture of the abscesses. Some recovered horses retain live bacteria in their guttural pouches (enlarged sacs which sit between the ear and the throat) and therefore become persistent ‘carriers’ of infection. These horses are risks to other susceptible horses.

The team of Vets at Cheltenham Equine Vets will help confirm the diagnosis by clinical examination and by the collection of samples of pus from the nose or lymph nodes for laboratory investigations, which can identify or rule out the specific Streptococcus equi organism.  This information will help your veterinary surgeon to advise you regarding appropriate treatment and management.

Strangles is rarely fatal but deaths can occur, most commonly associated with throat abscesses causing horses to die of pressure obstruction of the trachea (strangulation). At risk cases may require emergency elective tracheotomy (a hole is created surgically in the windpipe) to save their lives.

The blood test for Strangles: What does this look for. What do the results mean?

A blood test for strangles antibodies may also be taken. At Cheltenham Equine Vets we often use blood tests to screen for horses that have been in contact with strangles and have produced specific antibodies. A ‘positive’ result means that the horse has antibodies to the bacterium in its blood. This may reflect two main scenarios:

  1. Horses that have had the disease, have recovered and no longer show clinical signs
  2. Horses that have been challenged by contact with the organism but have never shown clinical signs

In both scenarios, these horses may or may not have
become carriers and therefore may or may not be risks to
other horses. Horses with unexpected positive blood 
antibody tests should therefore be specifically tested for
carrier status by guttural pouch washing and the washes submitted for strangles culture and DNA tests.

It is important to remember that it will take 2 weeks following first contact with a strangles case for a previously unchallenged horse to test positive. This must be considered when testing horses that may have had contact during an outbreak of strangles.

Some owners of racing and performance horse yards and stud farms use this test to screen incoming horses to identify carriers of strangles. Ideally, a negative test result should be obtained before the horse arrives.

Which horses can become affected?

Strangles can occur in horses of any age but younger horses are more likely to become infected and show clinical signs. 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 strangles be treated?

Certain antibiotics including penicillin can kill the bacteria that cause strangles but there is considerable disagreement as to if or when antibiotic treatment should be given to horses with clinical signs.

The problem with antibiotic treatment is that when abscesses form they produce a dense fibrous capsule which means that the antibiotics circulating in the bloodstream have difficulty in contacting and killing the infecting organisms in the abscesses. Thus antibiotic treatment may just tend to delay resolution of the infection. Experience suggests that antibiotic treatment may increase the risk of infection spreading to other lymph nodes throughout the horse’s body (miliary or ‘bastard’ strangles – see below). Therefore, many clinicians who have experience of dealing with strangles outbreaks often prefer to let the disease take its natural course. However some horses form such large abscesses that they are in danger of suffocation and for these cases, intensive antibiotic and anti-inflammatory treatment, and sometimes surgical tracheotomy, is essential to save their lives.

Recommended alternative treatments include application of hot towels or hot poultices (‘fomentations’) 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 cavities should be flushed with dilute povidone iodine solutions and allowed to heal naturally. Great care should be taken to thoroughly disinfect and dispose of pus and soiled swabs/paper towels from cleaning burst or lanced abscesses to prevent further spread of infection. Protective clothing (disposable gloves, boots, coveralls, etc) should be maintained specifically for infected cases and not used with other horses. It is essential that attendants and veterinary surgeons do not spread infection to other horses after they have handled, examined or treated an infected case. Ideally, separate staff should be detailed to look after infected horses only, applying appropriate biosecurity protocols. Your veterinary surgeon will help you with these matters.

In an outbreak all horses should remain on the premises to protect neighbouring yards and other equine communities. Cheltenham Equine Vets recommend the traffic light protocol which can be found on the Animal Health Trust website.


Horses are classified as being in RED, AMBER or GREEN groups.

RED – presumed infected horses that have shown clinical signs consistent with strangles or have been tested positive for Strangles.

AMBER – horses that have had direct or indirect contact with the infected horses in the RED group and as such are believed to have been at risk of exposure to S. equi but have not themselves shown clinical signs;

GREEN – horses that remained detached from those in RED and AMBER groups without known direct or indirect contact and which did not demonstrate clinical signs.

Can strangles be prevented?

It is very important to understand the highly contagious nature of this organism and to isolate infected cases to prevent further spread to other horses, both on and off the immediate premises. The team at Cheltenham Equine Vets will help you set up a management protocol appropriate to your own location and circumstances.

In an ideal world all newly arriving horses onto yards should be screened for the disease with the blood test. The gold standard would be to additionally quarantine new horses for 2-3 weeks and monitor their temperatures. However this is often not practical in the real world. Where horses come onto yards form unknown sources, especially where there are lots of different horses coming and going and young horses, it may be prudent to try to achieve this gold standard.

Isolation procedures

Any horse that shows suspicious signs of illness should be isolated until strangles
is confirmed or ruled out by veterinary examinations and
laboratory investigations. 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
appropriately instructed and equipped person should look
after the affected horse(s) and avoid contact with all other
horses. All in-contact equipment, stables, fences, trailers,
etc. should be thoroughly disinfected using a phenolic 
disinfectant. Protective clothing should be disposed of after each use or thoroughly disinfected and maintained specifically for infected cases and not used with other horses. It is essential that attendants and veterinary surgeons do not spread infection to other horses after they have handled, examined or treated an infected case. Once fully recovered, the horse can be turned out again but not in contact with susceptible horses until it has been proven not to be a carrier.

Strangles carriers

Unfortunately, some recovered horses become symptomless carriers of strangles, most commonly carrying the bacteria in their guttural pouches, and these can infect other in contact horses intermittently, whilst showing no signs of infection themselves. This is probably the most important cause of infection recurring at intervals of several months, after apparent clearance of infection or in a newly infected yard. Part of the clearance process for recovered cases should therefore be the collection of guttural pouch wash samples for laboratory investigations (bacterial culture and DNA testing – see above).

Strangles vaccination

A vaccine for the immunisation of horses against strangles was released in the UK by MSD Animal Health (Internet) but is not readily available. It is licensed to be used in horses at specific risk of infection to reduce the severity of clinical signs and the risk of spread of infection by reducing the occurrence of lymph node abscessation. It is given into the inside surface of the lip. The initial course is two injections given 4 weeks apart and boosters should be given every three months to maintain immunity. If the risk of infection is low, it may only be necessary to booster vaccinate every six months but this should be discussed with your veterinary surgeon, who may advise against the use of the vaccine. Additional vaccination may be required in the face of an outbreak. If vaccination is used, it is recommended that all horses in the same yard are vaccinated to minimise risk of disease. The manufacturers’ emphasise that the vaccine does not provide 100% prevention from infection or disease but they advise that it does reduce the severity of clinical signs, the occurrence of abscesses and the risk of spread of disease.

Are there other or long term complications of the disease?

Bastard Strangles

Although rare, Strangles can take a serious and unusual course with abscesses forming deep in an individual horse’s body. This is often termed ‘bastard strangles’ and can be very difficult to treat successfully. Affected horses may show signs of colic or abscesses may discharge internally from many sites. Cases lose weight and often require euthanasia on humane grounds with colic, respiratory distress or other complicating illnesses .

Carrier status

Occasionally a horse becomes a symptomless carrier and this has been discussed above. Often these carriers only spread the infection when they are stressed e.g. after transportation, being moved to a new stable yard or changing social groups.

Carriers can be treated (in isolation) by guttural pouch medication (involving repeated flushing with sterile saline and appropriate antibiotics) Some cases form infected hard lumps of pus in the guttural pouches. These are called ‘chondroids’ and need to be removed either using endoscopic instruments or in extreme cases with surgical intervention. Some of these cases can be very stubborn to treat. Successful treatment must be confirmed by guttural pouch washing at appropriate intervals after treatment has finished. Treated horses should not leave isolation until they are confirmed no longer to be carriers. This should be discussed with your veterinary surgeon.

Purpura haemorrhagica

Occasionally a horse that recovers from strangles will develop a condition known as purpura haemorrhagica. This is due to an unusual immune reaction to the streptococcal bacteria and it results in widespread damage to blood vessels, resulting in swelling of the legs and head and bruise-like patches in the mouth. Your veterinary surgeon should be called immediately if you suspect this life-threatening condition.

Code of Practice – Control of Strangles Infections

Since 1978, the Horserace Betting Levy Board has annually updated and produced its highly successful Codes of Practice for the control of a number of important equine contagious diseases, including guidelines on strangles. This guide contains detailed advice and recommendations on the disease and its effects, diagnosis, control and prevention. Your veterinary surgeon will have a copy of the Codes and they may be downloaded or used electronically from the HBLB website Here.

Although these are voluntary Codes they have become industry standards for the benefit of all. All horse breeders should read them and follow their advice.

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