The word strangles strikes fear into the heart of many horse owners, not only for its unpleasant symptoms and often long recovery process, but also for the wide-reaching implications caused by its highly contagious nature. However, despite the worry this disease creates and the stigma it carries, almost all horses recover completely, with a mortality rate of less than 2%.
Good hygiene, management practices and awareness are essential tools in safeguarding your horse against the most commonly diagnosed equine infection in the world, as is getting rid of the stigma attached to it, which can hinder quick and effective control of strangles.
What is strangles?
Highly contagious and difficult to manage, strangles is a non-airborne bacterial infection of the respiratory system caused by the bacterium Streptococcus equi (S equi). Scientists at the Animal Health Trust discovered that S equi has similar characteristics to the bacterium that causes human plague – in fact, strangles has many similarities to the plague. Thankfully, though, equine strangles poses no risk to human health.
Any age, breed or type of horse is susceptible to contracting strangles. However, young or old horses are often more likely to become infected with the disease due to their immune system being weaker and less able to fight off infection.
Older horses often exhibit a milder form of strangles with some nasal discharge and small abscesses, and their recovery process is sometimes faster than younger horses, who are more likely to develop severe abscesses. Horses with a history of other disease problems will also be particularly susceptible, again due to decreased immune strength.
Quick to spread
Strangles can be spread through direct contact with affected horses, or indirectly on items such as buckets or clothing. Although the bacterium doesn’t usually survive for long in the environment, especially on surfaces exposed to direct sunlight, it can survive for up to a month in drinking water.
What makes strangles such a challenging disease to manage and eradicate is that around 10% of infected horses become carriers, where even though they appear healthy and show no outward signs, they can be intermittently infective to other horses.
Carriers will have pus in their guttural pouches that has not been completely eliminated, and the bacteria in this pus can survive for months or even years, shedding out of the horse’s nose intermittently and causing other animals to become infected – the longest recorded time it has taken to eradicate the infection in a carrier is three-and-a-half years.
Signs of infection
In the initial stages of infection, your horse may not show any outward signs – clinical signs usually occur after 3–14 days, with abscesses forming up to two weeks after your horse has become infected. Horses who have been infected with the disease but are not yet showing any clinical signs are described as subclinical cases. The clinical signs include…
- high temperature of around 41°C
- nasal discharge that will start off clear, then become thick and coloured once the abscesses have ruptured in the nasal passages
- swollen lymph nodes and abscesses, mainly on the head and neck, which can cause difficulty breathing and swallowing
- loss of appetite
- loss of condition
Horses usually begin shedding the virus within two or three days of the onset of fever and, once they begin shedding, they are highly infectious. You should call your vet as soon as clinical signs appear, isolate every horse on the yard immediately, and restrict movement of horses on and off the yard.
While the signs of strangles are usually very evident, your vet will confirm the diagnosis by taking a swab from your horse’s nasal passages or guttural pouches to test for the bacteria. The use of blood testing for diagnosing acute strangles is limited because it will not show a positive result until two weeks after infection. However, it is a useful test for screening new arrivals and detecting carriers after an outbreak.
How he becomes infected
The bacterium enters your horse’s lymph glands via his respiratory system. The lymph nodes then swell and develop abscesses, which rupture (pictured left), shedding bacteria into the environment.
The bacterium may also be harboured in your horse’s guttural pouches, which are air chambers in his neck, just behind the skull and below the ears. The guttural pouches exist to cool the air going to his brain during heavy exercise and bacteria can enter them either via a natural opening from the throat, or because a swollen lymph node ruptures into the floor of the pouches, causing them to fill with pus.
What’s the prognosis?
The prognosis for most horses is very positive, with 98% recovering fully. The main problem is ensuring the infection is completely eradicated, which can take a long time and means your horse must be kept in isolation until he no longer carries any bacteria.
Complications can occur and, in rare cases, the infection spreads to other organs of the body, with abscesses developing and rupturing. This is called bastard strangles and with it the mortality rate rises to around 60%, because of the widespread infection and difficulties in treatment.
Another potential complication is purpura haemorragica, which is believed to be an immune-mediated complication of the lining of blood vessels, causing swelling (oedema) of the head, abdomen and limbs. It has a reported mortality rate of between 8 and 25%.
Treatment of strangles is very much on a case by case basis, with no one size fits all approach, however, supportive care is usually required, alongside impeccable hygiene and stable management. Once the lymph nodes swell and abscesses develop, your vet may recommend applying warm packs to help the abscesses mature.
The use of antibiotics in cases of strangles remains a topic of significant debate within the veterinary community, although their use with anti-inflammatories should probably only be considered in severe cases, where the horse has significant breathing difficulties.
Once the symptoms have subsided, to ensure your horse is bacteria-free, any chondroids (solidified pus) need to be removed from the guttural pouches. If chondroids are present, your horse may require a guttural pouch lavage – where the guttural pouches are washed out using an endoscope, then treated with antibiotics.
No animals should be allowed to arrive at or leave the yard until the cause of the disease has been identified and the outbreak has been brought under control.
In the event of an outbreak
As soon as strangles is suspected, your horse should immediately be put into isolation, so he has no contact with unaffected horses. While in isolation, ideally he should be able to see other horses but not come into direct contact with them. He must have a separate air space, which means keeping him out of the range of droplets that may pass through the air when a horse snorts or coughs. Strict isolation procedures are imperative to contain the disease and you should notify your yard owner or manager, as well as all other owners and carers, straightaway.
Horses who aren’t showing outward signs of strangles may still be infected if they’ve been in contact with an infected horse and should be isolated until your vet has proven that they are disease free. During this time, their temperature should be monitored at least once a day.
When caring for infected horses, you should…
- keep one set of equipment (such as a grooming kit, feed buckets and mucking out tools) for use on those horses and don’t use any of it elsewhere
- ensure the isolation area is only entered by those who need to care for the horses
- keep all other pets and animals well away, as they can spread the infection
- ensure potentially infected bedding and discarded forage, feed or water is disposed of in isolation – your vet will be able to offer advice on the best ways to do this
- wear strong disposable gloves and separate clothing – a set of overalls is useful for this and makes the process of changing significantly easier, especially if you also need to care for horses who aren’t infected
- wash your hands thoroughly using soap and water after any contact with horses in isolation, even if you have been wearing disposable gloves
- clean and disinfect your boots thoroughly when leaving the isolation area. A disinfectant footbath deep enough to cover your entire foot and ankle is recommended, and the contents of the footbath should be changed regularly because the disinfectant will not work if it’s dirty. Disinfectant spray can be a useful alternative to a footbath
- wash clothing or fabric items in your washing machine at 60°C to ensure any bacteria is killeddeal with horses in isolation last – this will not only help prevent the spread of disease, but will make things easier in terms of hygiene and care
It’s essential that you maintain isolation procedures until your vet gives you the all clear, because carrier horses who have recovered from the infection will show no outward clinical signs, but can still be highly infectious. Once you have the green light, you need to thoroughly clean and disinfect all equipment and any areas the horses have been in – paying close attention to the stable floor and walls, and any fencing the horse may have been in contact with. Your vet will be able to provide advice on the best disinfectant to use.
Getting the all clear
Declaring a yard clear of strangles can often be a long and drawn-out process that requires repeated testing to ensure the bacteria has fully left the horses’ systems. Different methods of testing include…
- blood testing This is useful for testing horses on affected yards who have not shown any symptoms, but for those who have contracted strangles, it will not be able to tell you whether a recent infection has cleared up. However, this test is important for declaring a premises disease-free, as it can identify animals who have become carriers.
The test was developed by the Animal Health Trust and identifies the presence of antibodies to S equi in the bloodstream. As well as identifying carriers, the test can identify horses who…
- are currently infected, although it takes approximately two weeks for a horse to develop antibodies against S equi, so it may not be possible to accurately identify infected horses in the very early stages of the disease
- have been infected with strangles in the last six months and have recovered
Animals testing positive should be investigated by nasopharyngeal swabbing or guttural pouch endoscopy to establish if they have S equi.
- nasopharyngeal swab A swab is used to collect pus or discharge from the nasal passages, which is then tested for the presence of bacteria. This relies on discharge being present in the nasal passages, which might not always be the case and doesn’t necessarily indicate that the infection has left the horse’s system.
- guttural pouch flush Saline solution is flushed through the horse’s nasal passages and the solution that comes out will be tested for bacteria. A flush can be more reliable than swabbing because it will collect bacteria throughout the nasal passages, even if the horse doesn’t have any discharge.
Infected horses should only be released from isolation after three consecutive negative nasopharyngeal swabs in a two-week period or one negative guttural pouch flush.
Will he develop immunity?
Around 75% of horses who have recovered from strangles develop a strong and long-term immunity to the disease, so the possibility of them becoming reinfected is quite slim. However, a small percentage of horses are susceptible to a second attack within several months of the first one, as their immunity has not yet fully developed.
When a new horse arrives at your yard, try to find out as much background information about him as you can, then check him over to ensure he appears healthy – for example, look at his body condition, skin condition, droppings and behaviour.
Remember that horses can carry disease without showing any signs, particularly in the early stages. For this reason, all new arrivals should be treated the same as sick horses and isolated for 21 days. This will reduce the risk to other horses should the new horse be carrying strangles and you should follow isolation procedures for this time until you and your vet are satisfied that the horse is disease-free.
Blood testing all new arrivals is a good way to keep your yard strangles-free, but it involves additional costs. Ideally, your vet will blood test the horse before he moves and he should only be moved if the test results are negative. However, because it can take two weeks from infection for strangles to show up on a blood test, there is a chance he could have just picked up the infection, so it’s wise to isolate him on the new yard for two weeks, then take another blood sample to confirm he is in the clear.
Is there a vaccination?
A vaccination for strangles is available, which is administered via an injection into the upper lip. It can be used from four months of age, and initially requires two vaccines one month apart, followed by boosters every 3–6 months. The vaccine can help prevent strangles, however, it should never be used as a substitute for good stable management, disease awareness and rigorous biosecurity. Your vet will be able to advise you as to whether the vaccine is appropriate for your situation.
Reducing strangles outbreaks
Preventing strangles is time consuming and often inconvenient, but these pale into insignificance compared to the costs of having to manage and resolve an outbreak. Together we can reduce the incidence of this dreadful disease, but only if there is a seismic shift in the attitude of all horse owners, and the totally counter-productive negative stigma attached to it changes once and for all.
- Keep a record of the date your horse first displayed signs of illness and any treatment provided by your vet. You should also record any recent outings (such as shows and hacks) and any contact with other horses, notifying their owners so they can be vigilant for any signs of infection. It is this transparency that is so often lacking in cases of strangles, and breaking this negative stigma and improving communication is essential in managing and containing outbreaks.
- Alert anyone who regularly comes onto your yard, such as your farrier, equine dental technician and feed supplier.
- Visit worldhorsewelfare.org/disease-prevention to download a Keep Your Horse Healthy pack, which has advice and tips for managing and preventing disease outbreaks.