Morgan Murphy

Deadly Fly Transmitted Diseases in Horses - The Nose to Nose Potentially Fatal Infection - Strangles

Flies carry infection, it is a simple concept - they land on one horse, pick up infection and fly on to the next, landing on the unsuspecting horse transmitting the infection it has picked up. But this kind of disease transmission can kill. Strangles can be deadly - It is one of the most contagious infections in horses and when just one fly moves infection from nose to nose, it is increasing the risk that the horse will contract this potentially fatal infection. For most horse owners, the word “strangles” is a concern – many of us understand that it is a serious condition and that there are implications of infection, but it is uncommon to come across new cases and we may not instantly recognize the condition when presented with it.

Strangles is found throughout the world and is a serious health concern owing to the speed at which it spreads. Every horse owner in the USA therefore has a duty to understand strangles’ origin, transmission and consequences, and to learn how to prevent the spread of this unpleasant disease.

What is strangles?

Strangles is an extremely contagious disease caused by Streptococcus equi bacteria. This bacterium affects the lymph nodes of the horse, to the extent that in some cases they become so swollen there is a compression of the trachea (windpipe) or pharynx (opening of the throat), causing respiratory problems.  S. equi spreads quickly and via numerous routes: primarily airborne, the bacterium can be spread through nose-to-nose contact, coughing, discharge, flies and the sharing of contaminated buckets, water sources, brushes and bedding.

The bacteria initially invade the horse’s tonsils, and within 3-8 days there will be clinical evidence of infection.  Not all horses that come into contact with the bacteria will become infected; vulnerability is dependent on the horse’s immune status, condition and age. Horses who regularly travel or are under stress are more prone to contracting strangles.

What are the signs of strangles in the horse?

The clinical signs of strangles are sometimes alarming. The most common symptoms to look out for are as follows:


  • a green/yellow thick mucus discharge from the nose
  • fever
  • reduced appetite
  • accumulation of pus in the lymph nodes, causing abscess
  • enlarged lymph nodes which eventually burst and seep a thick pus
  • depression and lethargy
  • cough
  • unusual head carriage - the horse can adopt a pose with his head and neck extended to relieve the pressure from the swelling
  • in very rare cases the lymph nodes in the rest of the body, such as in the chest, abdomen or even in the brain, can become infected - this is known as metastatic strangles.

Any suspicion that your horse has strangles should be reported to the veterinarian immediately. Your veterinarian will advise that you immediately isolate your horse and he or she will conduct tests to determine the presence of S. equi using swabs from the lymph nodes and nasal discharge.

How is strangles treated?

Once the abscesses rupture the horse can normally heal over a two-week period without the need for antibiotics. In some cases, fluid therapy is advisable. If the lymph nodes have not yet burst, an intensive nursing regimen may be implemented, utilizing heat compresses to draw out the fluid and encourage bursting and drainage. The horse must be kept in a warm, dry environment where he can rest and he should be encouraged to eat multiple small, palatable meals. It is vital he be segregated from other horses to prevent the spread of S. equi. The infected horse should be kept in isolation for 6-8 weeks and a strict hygiene regimen must be implemented to insure against cross-contamination. Adherence to this regimen is absolutely critical – all buckets, clothing and equipment must be sterilized after use

With the correct treatment, most horses can recover within 7-10 days, although they will remain infectious after resolution of clinical signs, hence the importance of the 6 to 8 week isolation period. The carrier status of the horse should be tested after this time using throat swabs, given that in some cases the horse will remain infectious for three or more months. The horse can be returned to the barn after three separate negative carrier swabs.

How do I prevent strangles?

Ideally, when a new horse arrives at your barn he must be isolated for two weeks in case any signs of strangles develop before he joins the existing group. If a new horse has come from a high-risk area, you should consider asking the veterinarian to perform throat swabs to check the horse’s carrier status. The doctor may then recommend vaccination. There are currently two types of vaccine available - an intramuscular injection and an intranasal vaccination – and these are intended for horses that are exposed to areas in which strangles has previously been identified, for example stables at shows or in yards with a confirmed case. The vaccine is not 100% effective but adopting a vaccination schedule according to risk as advised by the AAEP will help reduce the risk of both infection and spread.

All owners should be extra vigilant in looking for signs of contagious diseases such as strangles. Research is continuing into effective treatment and vaccination programs but, in the meantime, respecting isolation protocols, following strict hygiene procedures and eliminating cross-contamination will help to prevent the spread of this and many other diseases.


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