Strangles is a name that strikes fear into the hearts of all horse owners. Caused by the contagious bacteria Strep equi it is one of the oldest known diseases of the horse having been accurately described by the ancient Egyptians. Whilst it is a very infectious disease and can spread rapidly, with modern antibiotic treatment it is rarely fatal in this day and age. It can be a distressing disease for both horse and owner however sensible measures can minimise the risk of catching strangles and early prompt treatment can lessen the impact in the event of an outbreak. Once a horse has recovered from strangles it usually develops a strong immunity and it is rare for an animal to be affected more than once.
Strangles affects the upper respiratory tract i.e. the throat and its associated lymph glands. Being contagious means it can be passed from horse to horse. The name of Strangles is derived from the appearance of horses with advanced severe cases of infection when swelling of the lymph glands around the horse’s throat affect the ability to swallow, not only food but also saliva. In fact today we rarely see such advanced cases as Strep equi is 100% susceptible to penicillin. Strangles is spread between horses by the droplets in the cough of an infected horse, by the nasal discharges seen in many affected horses or by the pus which breaks out of the swollen lymph glands if they rupture. In the case of these secretions, they can be spread from horse to horse by sharing feed buckets, drinking water or on the coats of handlers. The time between infection and development of clinical signs varies but is usually 1 to 2 weeks. It is important to note that swelling of the glands or lymph nodes is NEVER present in the early stages of the disease. The commonest signs are depression, anorexia, a very high temperature, a soft cough and a slight yellowy nasal discharge.
Diagnosis Strangles is diagnosed primarily on the clinical signs which may be strongly suggestive of its involvement, particularly if there is more than one horse on the yard affected at the same time. There are many diseases that can give a horse a temperature and make it depressed, so it is important not to ignore the possibility of Strangles when these signs are present whilst not over reacting every time a horse has a temperature. Nasal swabs can be taken for examination in a laboratory for the presence of the Strep equi bacteria. If a swab is negative it does not mean the horse does not have strangles – often repeated swabs have to be taken at later dates before the bacteria is found. Recently a blood test has been developed which is able to tell us whether the horse has had contact with strangles in the recent past – this is a very different thing from saying the horse has strangles but there is no doubt this can be a very helpful test in determining which horses may be involved when an outbreak occurs on a yard. The blood test looks for antibodies in the blood against the strangles bacteria. Often owners (and some vets) confuse a positive test with being positive for infection. This is not the case. A positive blood test means that your horse has recently been exposed to the strangles bacteria and has either recovered or successfully resisted the infection. A blood test positive animal will enjoy a substantial period of immunity to future strangles outbreaks. Unfortunately we know that a small number of these blood test positive animals will become carriers.
Carriers For many years it remained a mystery as to how strangles outbreaks occur and how the bacterium survives from year to year. We now know that some horses can become carriers. Horses have two large air sacks to either side of the throat called the ‘guttural pouches’ these can become colonised by the strangles bacterium which form large lumps of pus called ‘chondroids’. Vets can detect these chondroids using an endoscope and can subsequently flush them out of the pouches.
Management If a horse is suspected of having strangles, it must be isolated immediately from all other horses on the yard to minimize possibility of spread. The horse should be boxed separately and the handler responsible for its care should wear waterproof overalls and not be coming in contact with any other horses until the overalls are removed and they have been thoroughly washed. There should be a disinfectant available outside the stable for the handler to dip their boots in (Virkon-S is effective).
The remaining horses on the yard should be divided into two groups – those that may have had direct contact with the initial case and those that haven’t. If possible these animals should be completely separated. This is usually virtually impossible on most livery yards. Responsible horse owners will wish to ensure that the bacteria don’t spread to other yards – so no horse should move on or off until at least three weeks after the last case has made a full recovery. It is recommended that all horses should have three clear swabs taken over a 21 day period before concluding that the outbreak is over.
Treatment If caught early in the course of the disease – called the septicaemic phase then treatment with penicillin for 4 to 5 days is highly effective. Usually pain relief with an anti inflammatory drug is very helpful. However once the glands begin to swell the use of antibiotics is more problematic. Some vets prefer to allow the disease to run its course. In some cases the strangles abscesses can press on the larynx reducing airflow. It this occurs (and it is very rare) then your vet will have to perform an emergency tracheostomy.
Bastard strangles One of the most serious consequences of strep equi infection can be the extremely rare disease ‘bastard strangles’. This is where abscesses form internally in areas such as the intestines or the lungs. This causes a progressive wasting disease and in most cases is fatal.
The future Currently there is no vaccine to protect against strangles in the UK. A few years back ‘Intervet’ launched an exciting new product that it hoped would protect against strangles. This required 6 monthly booster vaccinations but effectively only provided 3 months of immunity. Unfortunately technical difficulties with the vaccine led to its withdrawal from the market. At present the search for an effective vaccine continues.
The disease is spread via droplets from the nose of affected horses (nose-to-nose contact). Infection can also occur through close proximity of housing, shared equipment (water buckets, feed buckets, tack, twitches), rugs, people`s clothing and equipment of owners. The bacteria does not survive for long in the environment (up to 48 days at 20⁰c) although it can survive longer in moist and cold conditions. The majority of horses will only be infected with strangles once in their entire life, thereafter they will develop a strong immunity.
Control of an outbreak
- All horses in the premises should be screened for strangles – a reliable and quick blood test is available.
- A designated “dirty” area for the affected horses and a “clean” area for non affected horses should be created on the yard. These two areas should be well demarcated. The two areas should be separated from each other by at least two stables, and any contact between horses in the two areas should be prohibited.
- Movement of horses on and off the yard should be stopped and hygiene measures implemented immediately. People going from the dirty area to the clean area should disinfect their footwear and hands.
- Rectal temperatures should be checked every morning, on all horses in the premises. This is to identify possible new cases.
- Movement of convalescing horses from the “dirty” to the “clean” area should only be done after confirming that they are no longer shedding the bacteria. This can be achieved by bacterial culture from a nasal swab.
- New horses arriving on the yard should be placed under quarantine. During the quarantine period (3 weeks), the horse should be separated from other horses by a distance of at least one stable and any contact between horses should be prohibited. Check the temperature of the horse under quarantine every morning and also check for any nasal discharge or signs of inappetance or lethargy.
- Horses under quarantine should be screened for strangles.
- Some horses carry and spread strangles for long periods of time without showing any signs of disease – a nasal swab can be useful to detect these cases.
- Clean and disinfect hands between horses and when exiting the “dirty” area using an alcohol based hand sanitizer.
- Use easy cleaning footwear like wellingtons. Clean and disinfect footwear between horses and after exiting the “dirty” area with an appropriate disinfectant (e.g Virkon S ®).
- Feed and muck out the affected horses in the “clean” area first and then the horses in the “dirty” area. Do not move feeding buckets, hay nets, cleaning instruments, brushes and other material between “clean” and “dirty” areas. Clean and disinfect all the material mentioned above with an appropriate disinfectant (e.g Virkon S ®) at least twice a week.
If your horse is on a yard with other horses, it is your responsibility to inform the yard owner about the situation and the affected horse should be separated from others to avoid an outbreak.