Strangles
A highly contagious bacterial infection where early isolation and good biosecurity can make an enormous difference
Strangles is one of the best-known infectious diseases of horses. It is caused by the bacterium Streptococcus equi subspecies equi, often shortened by vets to Strep. equi or S. equi.
The infection commonly affects the lymph nodes — the small glands involved in the immune system — around the horse's head and throat. These can become enlarged, painful and filled with pus, sometimes forming abscesses that eventually burst and drain.
The name strangles comes from the fact that severe swelling around the throat can, in serious cases, interfere with swallowing and breathing.
Although the appearance of an affected horse can be alarming, most horses recover. The major challenge with strangles is how easily infection can move between horses and how apparently healthy horses can sometimes continue carrying and spreading the bacteria.
If you suspect strangles, isolate the horse immediately and contact your vet. Do not wait for a positive test before taking precautions.
At a glance
Cause: A bacterium called Streptococcus equi subspecies equi
Spread: Mainly through direct contact with infected horses or indirect contact with contaminated equipment, water, surfaces, clothing and people
Common early warning: A raised temperature is often one of the first signs
Typical signs: Fever, dullness, nasal discharge, swollen glands around the jaw and throat, difficulty swallowing and abscess formation
Can apparently healthy horses spread it? Yes. Horses can spread infection before obvious signs develop, and some recovered horses become symptom-free carriers.
What should you do? Isolate the horse, stop unnecessary movement and contact your vet.
What causes strangles?
Strangles is caused by Streptococcus equi subspecies equi.
It is a bacterial infection, not a virus.
The bacteria enter the horse, usually through the nose or mouth, and become established in tissues associated with the upper respiratory tract. Infection can then involve nearby lymph nodes.
You may hear your vet use the term lymphadenopathy. This simply means enlarged or swollen lymph nodes.
When infected lymph nodes fill with pus, your vet may describe this as lymph node abscessation — in everyday language, an abscess has formed within the gland.
How does strangles spread?
Strangles is highly contagious.
It can spread directly when an infected horse has close contact with another horse, particularly nose-to-nose contact.
It can also spread indirectly when infectious nasal discharge or pus contaminates objects or surfaces.
These may include:
- water buckets and troughs
- feed buckets
- stable doors and gates
- grooming equipment
- tack
- rugs
- headcollars and lead ropes
- horseboxes and trailers
- veterinary or yard equipment
- people's hands
- footwear
- clothing
This type of contaminated object is sometimes called a fomite. If your vet says that infection may have been transmitted by fomites, they simply mean that something contaminated with infectious material has carried the bacteria from one horse to another.
This is why biosecurity is so important during a suspected outbreak.
What are the signs of strangles?
Not every horse develops the classic textbook signs.
Some horses become obviously unwell, while others may have relatively mild symptoms.
Signs can include:
- raised temperature
- dullness or lethargy
- reduced appetite
- difficulty eating or swallowing
- thick nasal discharge
- coughing
- swollen and painful glands beneath the jaw or around the throat
- abscesses that subsequently burst and discharge pus
- holding the head or neck in an unusual lowered position because swallowing is uncomfortable
A horse's normal temperature varies, which is why knowing your own horse's usual resting temperature can be useful.
During a suspected outbreak your vet may recommend taking temperatures twice daily to identify horses developing fever before other obvious symptoms appear.
“Hot before snot”
You may hear the expression “hot before snot” used in strangles awareness campaigns.
It is a useful reminder that a rise in temperature can occur before the obvious nasal discharge and swollen glands that owners traditionally associate with strangles.
This creates an important opportunity.
Identifying and isolating a horse at the fever stage may help prevent that horse having close contact with others while infection is developing.
However, fever has many possible causes. A raised temperature does not automatically mean that a horse has strangles.
Not every horse looks seriously ill
One of the difficulties in controlling strangles is that infection does not always produce dramatic symptoms.
A horse may have only:
- a mild temperature
- slight nasal discharge
- reduced appetite
- mild lethargy
You may hear this described as subclinical infection or atypical strangles.
Subclinical means that infection is present but the usual clinical signs are absent or so mild that they may easily be missed.
A mildly affected horse can still be important from a disease-control perspective, so unexplained respiratory signs or fever should not simply be dismissed when strangles is a possibility.
What should I do if I suspect strangles?
Do not wait for confirmation before taking precautions.
Move the affected horse away from other horses as safely as possible and contact your vet.
Your yard may need to:
- stop horses moving on and off the premises
- separate affected, exposed and apparently unaffected horses
- use separate equipment for each group
- prevent shared water and feed equipment
- monitor temperatures
- control the movement of people between groups
- clean and disinfect appropriate equipment and surfaces
- inform people whose horses may have been exposed
Your vet will help establish the appropriate testing and disease-control programme for the circumstances.
On a larger yard, you may hear horses described using a traffic-light system.
Red generally refers to infected or clinically suspicious horses.
Amber refers to horses that may have been exposed.
Green refers to horses considered at lowest risk or currently unaffected.
The precise arrangements should be determined for the individual yard with veterinary guidance.
How is strangles diagnosed?
Clinical signs can make a vet suspicious of strangles, but laboratory testing is normally needed to confirm infection and to help manage an outbreak.
One test you are likely to hear about is PCR.
PCR stands for polymerase chain reaction. In simple terms, it is a laboratory technique used to look for genetic material from the bacterium.
Depending upon the stage of infection and circumstances, your vet may collect samples from the respiratory tract or other appropriate sites.
An early negative test does not necessarily rule out strangles because the amount of detectable bacteria can vary during the course of infection. Your vet may therefore recommend repeat sampling.
You may also hear the term culture. This means attempting to grow bacteria from the sample in a laboratory so they can be identified.
PCR and bacterial culture provide different information, so your vet will determine which testing approach is appropriate.
What are the guttural pouches?
The guttural pouches are two large air-filled sacs situated deep within the horse's head, close to the throat.
They are normal anatomical structures found in horses.
They become particularly important in strangles because infected material can enter the guttural pouches when nearby abscesses drain.
In most horses the infection eventually clears.
In some, infected material remains.
Your vet may use an endoscope — a long, flexible instrument containing a camera — passed through the nose to examine the guttural pouches.
This is called guttural pouch endoscopy.
A fluid sample can also be taken from the pouch for laboratory testing.
What is a strangles carrier?
Most horses eventually eliminate the infection, but a minority can continue harbouring S. equi after appearing to recover.
These horses are known as carriers.
A carrier may look completely healthy while continuing to harbour bacteria within the guttural pouches and potentially shedding infection intermittently.
This is one of the reasons strangles can unexpectedly reappear on a yard.
Carrier horses may remain infected for months or, in some cases, much longer.
What are chondroids?
This is another term owners may hear from their vet.
Pus remaining within a guttural pouch can gradually become thicker and form firm, rounded masses.
These are called chondroids.
Despite the unfamiliar name, they are essentially hardened or dried accumulations of infected material within the guttural pouch.
Strep. equi can survive within this material, allowing an apparently recovered horse to remain a carrier.
Your vet can examine the guttural pouches with an endoscope and, where necessary, treat persistent infection and remove retained material.
When is a recovered horse safe to mix again?
The disappearance of symptoms does not necessarily mean that a horse is no longer infectious.
Recovering horses can continue shedding S. equi after they appear clinically well, and some become longer-term carriers.
For that reason, returning a horse to normal contact should not simply be based on the horse looking better.
Your vet will advise when testing should be undertaken and what testing protocol is appropriate.
Guttural pouch examination and testing can be used to identify persistent infection. In some circumstances, repeated nasopharyngeal sampling may be used instead.
Veterinary clearance, rather than appearance alone, should determine when a horse can safely leave isolation.
Can strangles cause complications?
Most horses recover, but complications can occur.
Severe swelling or abscess formation around the throat can interfere with breathing or swallowing.
In a small number of cases, infection can spread beyond the lymph nodes around the head and neck and cause abscesses elsewhere within the body.
You may hear this called metastatic strangles or the older veterinary term “bastard strangles.”
Metastatic simply means that infection has spread to other locations.
Another uncommon but potentially serious complication is purpura haemorrhagica.
This is an abnormal immune reaction that can cause inflammation of blood vessels and substantial swelling, often involving the limbs, underside of the body or head.
These complications require veterinary attention.
Difficulty breathing, severe difficulty swallowing, marked swelling, profound weakness or rapid deterioration should always be treated as urgent.
How is strangles treated?
Treatment depends upon the individual horse, the stage of infection and the severity of disease.
Many uncomplicated cases are managed with veterinary supervision, nursing care and careful monitoring while the horse's immune system deals with the infection.
Management may include making the horse comfortable, providing food and water that are easy to consume and managing developing abscesses appropriately.
Antibiotics are not automatically required for every case of strangles.
Whether antibiotics are appropriate can depend on the stage and severity of infection and the individual horse. This decision should therefore be made by the attending veterinary surgeon.
Never give leftover antibiotics or medication intended for another horse.
Biosecurity matters as much as treatment
With strangles, looking after the individual horse is only part of the job.
Preventing infection moving to the next horse is equally important.
Where possible:
- keep isolated horses physically separated
- use clearly identified equipment for each group
- do not share water buckets or troughs between isolation groups
- attend to unaffected horses before infected or suspect horses
- wash hands thoroughly between groups
- clean and disinfect footwear and appropriate equipment
- use protective clothing where advised
- prevent contaminated equipment leaving the isolation area
- restrict unnecessary visitors
- tell visiting professionals about the situation before they arrive
This last point is particularly important.
Vets, farriers, dentists, physiotherapists, therapists, trainers and other visiting practitioners need to know that strangles is suspected or confirmed so they can assess whether the visit should proceed and put suitable biosecurity measures in place.
New horses and prevention
One of the most effective opportunities to prevent infectious disease entering a yard is before a newly arriving horse mixes with the resident population.
A sensible new-arrival protocol may include:
- a period of isolation
- separate equipment
- separate water
- daily health observations
- regular temperature monitoring
- appropriate testing based on veterinary risk assessment
Current guidance commonly recommends isolating new arrivals for approximately 14–21 days, although the appropriate protocol depends upon the individual situation and veterinary advice.
Testing for silent S. equi carriage may also be considered before a new horse joins an established group.
What about vaccination?
Vaccination against strangles is available in the UK.
Vaccination does not mean that a horse can never become infected, but it can form part of a risk-based disease-prevention programme.
Whether vaccination is appropriate, when it should be given and how it fits alongside testing or management of an outbreak should be discussed with your veterinary surgeon.
Vaccination should complement good biosecurity rather than replace it.
Strangles is a disease — not a reason for stigma
One of the biggest barriers to controlling strangles is sometimes people's reluctance to tell others that they have a suspected or confirmed case.
An outbreak is not automatically evidence of a badly managed or dirty yard.
Horses travel, compete, train, change yards and come into contact with other horses and people. Even well-managed premises can experience infectious disease.
Rapid isolation and open communication protect other horses.
Owners and yard managers who identify a problem and act responsibly should be supported rather than blamed.
When should I call my vet?
Contact your vet if your horse develops signs that could indicate strangles, particularly:
- an unexplained raised temperature
- swollen glands around the jaw or throat
- thick nasal discharge
- difficulty swallowing
- abscesses around the head or neck
- respiratory signs following contact with an affected or potentially exposed horse
If strangles is suspected, isolate first and telephone your vet rather than moving the horse through the yard unnecessarily.
Seek urgent veterinary assistance if the horse is having difficulty breathing, cannot swallow properly or is deteriorating rapidly.
Key message
Strangles is highly contagious, but outbreaks can be controlled.
The most important actions are:
Recognise → Isolate → Call your vet → Control movement → Test → Clear infection before mixing again
A horse looking recovered is not necessarily free from infection.
Good biosecurity, appropriate testing and responsible communication protect not only your own horse, but every horse with which your yard has contact.
Suggested graphics
Graphic 1 — Hero graphic
STRANGLES: RECOGNISE IT EARLY. STOP IT SPREADING.
Visual concept:
A clear, sympathetic illustration of a horse's head and upper neck with subtle highlighting of the lymph-node areas beneath the jaw and around the throat. Alongside the horse, show four simple warning-sign icons:
Raised temperature • Nasal discharge • Swollen glands • Difficulty swallowing
Main message:
Suspect strangles?
ISOLATE FIRST — THEN CALL YOUR VET
Small supporting line:
Strangles is caused by the bacterium Streptococcus equi. Early isolation can help protect every horse on the yard.
Footer:
JCG Equine Health Hub | jcgsupplements.com
The graphic must contain sufficient information to remain meaningful if saved, shared or printed separately from the webpage.
Graphic 2 — How strangles spreads
ONE INFECTED HORSE — MANY POSSIBLE ROUTES
Central infected-horse illustration with lines leading to:
Horse-to-horse contact
Water buckets & troughs
Grooming kit & tack
Stable doors & gates
Horseboxes & trailers
Hands, footwear & clothing
Bottom message:
Strangles doesn't need horses to touch directly.
Contaminated equipment, water and people can move infection between horses.
Separate horses. Separate equipment. Control movement.
Footer:
JCG Equine Health Hub | jcgsupplements.com
This graphic should work as a standalone biosecurity poster suitable for printing in a tack room or yard.
Graphic 3 — What to do if you suspect strangles
SUSPECT STRANGLES? SIX ACTIONS THAT HELP PROTECT THE YARD
1 — ISOLATE
Separate the suspect horse immediately.
2 — CALL YOUR VET
Don't wait for a positive test before taking precautions.
3 — STOP MOVEMENT
Avoid horses unnecessarily entering or leaving the yard.
4 — SEPARATE
Keep infected/suspect, exposed and unaffected horses apart and use separate equipment.
5 — MONITOR
Your vet may recommend twice-daily temperature checks.
6 — COMMUNICATE
Tell your yard manager and warn vets, farriers, dentists and other visiting professionals before they attend.
Bottom panel:
LOOKING BETTER DOESN'T ALWAYS MEAN INFECTION HAS GONE
Recovered horses may require veterinary testing before they can safely mix with others.
Footer:
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The graphic should be designed so it can be printed as an A4 yard notice without needing the accompanying webpage for explanation.
Important
This page provides general educational information and does not replace veterinary diagnosis or treatment.
Strangles is an infectious disease. If you suspect your horse may be affected, isolate the horse and contact your veterinary surgeon for advice on diagnosis, treatment, testing and biosecurity.