What is Strangles?
Strangles is one of the most prevalent infections equine diseases diagnosed worldwide. It is a bacterial infection involving the upper respiratory tract and the lymph nodes of the head and neck caused by the bacterium Streptococcus equi.
Despite significant advances in diagnosis, treatment and control there are still challenges involving the identification and treatment of subclinical carriers and also vaccination development. It remains a widely feared disease because of its debilitating effects and potential for major economic losses to yards and owners.
HORSES AT RISK
Young horses (1-5 year olds), older horses and horses that are already sick or debilitated are more susceptible but it is important to remember all horses are at risk of contracting the disease.
Signs of the disease develop between 3-14 days after contact with the infection and vary widely between individual horses, some may show no signs at all, but can present with:
- Depression or dullness
- Pyrexia (high temperature)
- Loss of appetite (anorexia)
- Nasa discharge
- Lymph node (gland) swelling under the jaw or on the head or neck which can develop into an abscess at a later stage.
If an abscess does form it is usually 1-2 weeks after first contact with the infection. Abscesses can last for 3-4 weeks, in a few cases horses can be ill for 1-2 months. When they burst these abscesses discharge highly infectious thick, creamy yellow pus.
It is important to remember that horses can start to spread the disease before clinical signs appear. Most horses recover and the condition is rarely fatal (less that 1% of infected horses die from this condition). 75% of cases will become resistant to re-infection for up to 5 years after they have recovered.
Enlarged lymph nodes can swell so much that they restrict the airway, this complication gives the disease it’s name, Strangles. Enlarged lymph nodes are sometimes internal and can lead to respiratory distress and an inability to eat.
Guttural pouch empyema and chondroids are hard lumps of pus in the guttural pouches which have to be removed endoscopically or surgically.
In a small number of cases the infection causes abscesses to form in the lymph nodes and organs around the body. When abscesses spread around the body like this the condition is called bastard strangles and horses can present with colic.
Purpura Haemorrhagica is an unusual immune reaction to the Strep Equi bacteria which usually occurs 1-4 weeks after a horse has apparently recovered from strangles. It causes widespread damage to blood vessels, oedema (swelling), bruise like patches on the mouth, bleeding into gums and organs e.g. Lungs. When horses develop this complication it is often fatal.
SPREAD OF INFECTION
Contrary to popular belief Strangles is not an airborne disease but is easily spread by both direct contact, from horse to horse, or indirectly via contact with contaminated equipment as well as human handlers, yard animals and within the environment. This can lead to large scale outbreaks if strict bio security measures are not adhered to.
Horses with acute infection start to shed bacteria 2-3 days after developing a fever. Nasal shedding persists for 2-3 weeks but infected horses should be considered a potential source of infection for at least 4-6 weeks after clinical signs have resolved. Some horses can continue to shed bacteria for longer than this without necessarily having nasal discharge (they become carriers) – this is why it is critical to look in the horse’s guttural pouch via an endoscope at this stage to ensure infection has cleared.
The infection can also live outside of the host for a time. It is not very persistent within the outside environment, surviving for only 1-3 days, but in water it can persist for a month. Contaminated paddocks should be rested for at least 4 weeks before they can be considered not infectious.
Some of the ways the infection can spread are:
- Nose to nose contact between horses
- Feed buckets
- Water troughs
- Grooming equipment
- Contaminated handlers moving from stable to stable
A blood test may be taken to look for the horse’s immune response to Strep Equi bacteria. It should be noted it can take up to 14 days for the immune response to show on the blood test, and therefore two blood tests, 14 days apart, may be necessary if the first one is negative.
Samples may be taken from the infected horse, wither from abscesses, nasopharangeal swabs (back of the nose) or from a guttural pouch wash. These samples are then cultured to look for a living organism. It can take up to a week to get results as it takes time to grow the bacteria in the laboratory and identify the exact type of bacteria that is present. Culturing the bacteria is considered the gold standard in Strangles diagnosis. A PCR test may also be done to look for Strangles DNA, although this will also detect dead bacteria and therefore is usually used in conjunction with the bacterial culture.
Generally, it is advisable to let the disease run its course with the horse in isolation, implementing a strict bio security protocol and with the aid of supportive therapy, such as Non Steroidal Anti-inflammatory relief e.g. Bute. If lymph node abscessation occurs, then hot packs should be applied to provide relief and encourage the abscess to rupture. Once an abscess has burst it should be flushed with dilute hibiscrub and then left to heal.
The use of antibiotics for treating the infection is controversial and can lead to development of complications mentioned previously and can also prolong abscess maturation and rupture delaying the resolution of the disease. If the horse is very sick and there are internal abscesses causing secondary problems such as respiratory disease, then antibiotics may be prescribed.
Treatment is available for carriers to remove the persistent infection and, once removed, horses continue to lead healthy lives posing no further risk of infection.
In a perfect world we would perform a guttural pouch lavage on all horses before moving onto a new yard. But it is an expensive procedure to perform routinely. Horses moving onto a new yard should be isolated for a minimum of 2 weeks with no direct between a new arrival and other horses for equipment used for or by other horses. Performing a blood test on new horses can help to detect carriers.
A vaccine is currently available may not be good enough to recommend as a reliable prevention method. The manufacturers own data indicated vaccine failure in about a quarter of cases and there is an associated increased risk of Purpura Haemorragia. Vaccinated horses are likely to get systemic disease if they already have the disease, therefore owners need to blood test and isolate them prior to giving the vaccination.
If you have any suspicions that your horse may have Strangles please contact your vet immediately.
Contributor: B&W Equine Vets