Strangles

What is strangles?

Strangles is a highly contagious, bacterial infection of the upper respiratory tract caused by Streptococcus equi equi.  The disease can affect horses, ponies and donkeys of all ages. Although the disease can make affected horses quite unwell for a couple of weeks, most make a full recovery. It is the highly contagious nature of strangles and the potential to shut down yards for weeks or even months that tends to cause the stigma that can surround the disease.

Clinical signs

• A high temperature, usually at least 39-40°C (this is usually the first clinical sign to occur).
• Depression and loss of appetite.
• Nasal discharge (usually watery to begin with but becoming thick pus within a few days).
• A cough.
• Swollen and painful lymph nodes in the throat area which can develop into draining abscesses.
• Difficulty in swallowing.
• Difficulty in breathing and abnormal respiratory noises.

It is important to recognise that not all horses show all of these signs; some may simply have a high temperature and seem off colour. Clinical signs tend to develop about 7-14 days after infection, but can occur as little as 3 days or as long as 21 days after infection.

Once infection develops most horses will be unwell for 1-3 weeks. After this time, the vast majority will make a full recovery, though around 10% of cases may develop complications that can be more serious. These include purpura haemorrhagica which is a serious illness of the immune system, and bastard strangles where abscesses develop in internal organs.

Another small proportion of affected horses will appear to make a full recovery but will continue to harbour infected material in their respiratory tract. These horses appear outwardly healthy but can shed bacteria intermittently for a number of years. These horses (known as carriers) are an important potential source of infection to other horses.

How is strangles spread?

Strangles spreads principally by direct physical contact with an infected horse (either an active case or a carrier).  Generally, horses do not begin to shed bacteria until 24 hours after developing a fever. They are at their most infectious when they have a thick nasal discharge or a draining abscess. Affected horses can however continue to shed bacteria for a few weeks after all their symptoms have resolved, or for several years if they become a carrier.

Strangles can also be spread by indirect contact. This means the infection is spread by infected material (nasal discharge or pus from a draining abscess) from one horse to another via a person or object. Common examples would be a water trough, feed bucket or on a handler’s hands, feet or clothing. The bacteria that cause strangles can linger for a number weeks in the environment (particularly in water).

Fortunately, this infection is not airborne so, unlike influenza, it will not spread long distances without some kind of direct or indirect contact.

What should I do if I suspect my horse has strangles?

If you suspect strangles, you should isolate your horse immediately. Ideally this should be in a completely different building where there is no contact with other horses, but otherwise the horse should be placed in a stable or paddock where it cannot make nose to nose contact with another horse. You may need to move horses away from neighbouring stables or double fence a paddock in order to achieve this.

You should use separate feed and water buckets, head collars and other equipment for this horse only. Do not touch other horses until you have thoroughly washed your hands and have changed your outer clothing and footwear. Once isolated please arrange for a vet to examine your horse so we can discuss diagnostic tests and advise on treatment.

How is strangles diagnosed?

There are a number of different ways that your vet may test your horse for strangles. If nasal discharge or a draining abscess is present, they will take a swab of the discharge and test for the presence of Strep. equi.  If there is no visible nasal discharge they may use a long swab (called a nasopharangeal swab) which is inserted up the nostril to take a sample from the throat region. They may also take a blood sample to test for presence of antibodies against Strep equi, although these antibodies can only be detected in the blood stream from around 2 weeks after the horse was exposed to strangles.

Guttural pouch endoscopy allows your vet to see into and take samples from the guttural pouches at the back of your horse’s throat. This is where strangles bacteria can linger after a horse appears to have recovered. This is the best method of confirming a horse that has had strangles is no longer infectious. It is also how we identify carriers.

What should I do in the event of a strangles outbreak?

If your horse is confirmed to be positive for strangles, your vet will advise on what procedures need to be put in place for the rest of the premises and how it will affect other horses on your yard. As well as isolating the affected horse, it is important that all horses that have been in direct contact with that horse are placed in isolation as well as they may be incubating the disease. These horses should have their temperatures monitored twice daily.

Other horses that may have been in indirect contact with the infected horse should also be monitored closely for clinical signs and should not be moved off the yard. This usually means that at the start of an outbreak all horses on an affected yard will need to have their temperatures monitored and will not be able to move off the yard until the spread of the disease has been contained.

What can I do to help my horse if he is suffering from strangles?

• Give soft, wet, palatable feed that is easy to swallow with a sore throat.
• Give Phenylbutazone (‘bute’) as directed by your vet to lower their temperature and reduce throat soreness.
• Put the hay and feed on the ground to aid drainage of discharges.
• ‘Hot-pack' firm abscesses to encourage them to soften and burst. This may provide relief to the horse when the pressure building up is released and will speed up healing.

Once your horse appears to have made a full recovery you should continue to isolate your horse until he or she has been tested to confirm they are free of strangles. Your vet will advise on the best timing of this but is usually done 4-6 weeks after the last clinical sign, and is best done by performing a guttural pouch wash.

Disease prevention

When travelling to shows etc. there are some simple measures you can take to reduce the risk of your horse becoming infected with strangles.

• Use your own buckets, water and feed.
• Do not allow other horses to share buckets.
• Avoid nose to nose contact with other horses.
• Wash your hands between horses when handling other horses.

At home, it is advised that you should isolate all new arrivals for 3 weeks, watch for clinical signs and monitor rectal temperature once daily. If they develop nasal discharge, increased temperature or throat swellings then it should be tested for strangles. In high risk situations (e.g. if your horse is stabled at a large yard) it is prudent to perform a guttural pouch wash on all new arrivals to check they are not carrier before taking the horse out of isolation.

Image courtesy of Redwings Horse Sanctuary

This article also appears on the Horse Health Programme website.