Silent killers:  Strangles

Strangles in horses is one of the most common infectious equine diseases in the UK.  Treatments are available, but two of the most important elements of the battle against strangles are biosecurity and awareness.

While not typically life threatening, strangles is a distressing disease for both horse and owner and is fatal in up to 10% of cases.  Affecting all types and ages of horse, pony and donkey, it is an infection of the upper respiratory tract caused by the bacteria Strep.equi (Streptococcus equi subspecies equi).  Typical symptoms include a temperature above 38.5°C, depression, loss of appetite and thick, yellow mucus draining from both nostrils.  Additionally, hot and painful abscesses may develop on the sides of the head and throat and the horse may experience difficulty eating or extending the head due to discomfort in the throat – hence the name strangles.

Strangles’ incubation period is usually three to 10 days but can be up to 14 and it can take up to a week more for abscesses to appear.  The condition will typically last for at least three weeks if untreated and following recovery, around one in 10 affected horses will become carriers and can intermittently shed bacteria for long periods afterwards.  Complications also develop in up to 20% of cases which can include infection for months rather than weeks or, more rarely, ‘bastard’ (metastatic) strangles, where abscesses form elsewhere on the body, and the immune system disorder purpura haemorrhagica.

Initial diagnosis is made by a vet based on clinical signs but this is generally followed up by lab tests for confirmation.  Good quality nursing is generally the only treatment that will be required, with rest and the use of anti-inflammatories.  Strangles vaccines are available and can both reduce the chance of infection and the severity of symptoms if infected.

Such is the prevalence of strangles that since 2018 the Royal Veterinary College has been running a research project, Surveillance of Equine Strangles (SES), sponsored by The Horse Trust.  This project investigates where in the UK strangles is being diagnosed and is designed to better understand the dynamics and control of the disease.  Between January 1 and August 2 2022, 86 veterinary practices submitted samples to SES laboratories, with 205 diagnoses being reported.  Of the equines diagnosed, 36% were UK native pony breeds and 22% UK native horse breeds.

The key issue with strangles is the ease with which it can be transmitted.  The bacteria are primarily spread by direct contact with an infected animal, but this is not limited to horse-to-horse contact.  While not airborne, the bacteria can spread via a third party, on people’s hands or clothing, on equipment or tack, via shared water troughs or even grazing on an area previously grazed by an infected animal.  

The single most important weapon in the battle against strangles in the broader equine world is isolation of infected animals and adherence to tight bio-security measures.  This can mean that, for example, owners of yards with strangles having to impose lockdown for the duration of infection.  Unfortunately, because of the knock-on economic effects for commercial operations such as riding schools, there is sometimes a reluctance to admit that strangles is present, but suppressing the information risks spread of the disease. 

While strangles can pose a challenge for horse owners and yard managers, it is a relatively straightforward process to put in place quarantine and bio-security measures, which are often simple, practical steps for horses and ponies in a confined environment.  However, strangles can also pose a threat to the herds of native ponies that live out and roam free in semi-wild situations where herd management is very much ‘hands off’.

Herds on Dartmoor and in the New Forest, for example, have experienced strangles and as well as finding an effective way of treating the affected ponies, those responsible for the management of these herds have to contend with the additional challenges posed by public access.  With some grazing ponies used to interacting with members of the public, transmission of strangles by someone who has petted an infected pony is all too easy.  Similarly, riders using bridle paths across grazed areas could be inadvertently picking up and passing on the bacteria.

The equine charity Redwings is at the forefront of efforts to beat the spread of the disease.  It runs the Strangles Hub which provides a wealth of information and advice, including diagnosis, treatment and prevention measures.  Redwings’ Head of Welfare and Behaviour, vet Nic de Brawere regularly shares his knowledge of strangles and effective biosecurity and was one of a panel of experts who developed the current best practice guidelines for strangles diagnosis and management published in 2021.  Another initiative is the Strangles Awareness Week, a global collaborative effort to prevent and manage the disease.  In the 2022 week, horse owners were asked to take the ‘Temperature Check Challenge’, by taking their horse’s resting temperature each day and inputting the reading into an online checker to help them get to know their horse’s normal range.  Ongoing regular checks can then alert the owner to the high temperature that is an early warning sign of strangles infection.

Strangles is a disease that can only be stamped out by concerted action across the horse world.  Routine biosecurity measures should include quarantining of newly introduced horses for two to three weeks and being infection-aware when travelling and at events.  If a horse or pony has been infected, they should be checked by a vet as they recover so that potential carriers can be treated effectively.

 If the worse does happen and an outbreak occurs on your land or premises, you should communicate openly about the disease.  In its guide to strangles, “Strangles Speak Out!”, Redwings says:  “Strangles has been associated with an unhelpful, unjustified stigma which encourages owners to hide the disease when it affects them.  In fact, speaking out about possible infection is a vital part of a proactive response that will help to stop the spread and support good practices on yards.”

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