By vet Bethan Harper
Strangles is a respiratory infection of horses caused by the bacteria Streptococcus equi subsp. equi (S. equi).
It is highly contagious and is spread by direct contact between horses, or through contamination of shared equipment such as feed buckets and water troughs.
People can also spread the disease if they move between infected and non-infected horses.
The characteristic signs of strangles are a rectal temperature over 38.5°C and abscess formation in the lymph nodes around the head and neck giving a swollen appearance. These abscesses can get extremely large which is painful for the horse and may restrict their ability to swallow or breathe. Once the abscesses burst, highly infectious pus is released into the environment. Horses may also have discharge from both nostrils, a soft cough, general signs of lethargy and loss of appetite. In some cases, the abscesses can form and burst internally, which has more serious effects.
In order to confirm a diagnosis of strangles there are several tests that your vet might decide to do. Where there are burst abscesses present, these can be swabbed either to culture the bacteria, or do a test known as PCR which can identify S. equi DNA. Samples can also be taken by swabbing the nasopharynx at the back of the throat, or by performing a guttural pouch wash which is done using an endoscope. A blood test is also available to detect antibodies for S. equi indicating exposure to the disease.
Due to the incubation period of the bacteria (the time between being infected and symptoms showing) it is possible for the disease to spread before it is identified. For this reason, it is important that as soon as a case of strangles is diagnosed appropriate measures are taken to reduce the spread.
If a case is detected, a traffic light system should be adopted where horses are split into red, amber, and green groups. The red group includes all horses that have been diagnosed with strangles or are showing clinical signs. These horses should be isolated away from other horses and should be attended to last in the daily rounds or ideally have a separate set of staff to attend them. The amber group contains all horses who have been in contact with the red group in the last 3 weeks and the green group are the horses who have not had any contact with the red group. All horses in the green and amber groups should be carefully monitored and have their temperature taken twice daily in order to identify the first signs of infection, and strict biosecurity should be adhered to.
In most cases, no specific treatment is required for horses with strangles and horses recover well with nursing care, but it is important to seek advice from your vet to discuss your individual case. Although most horses recover well from strangles, approximately 10% will be persistently infected and act as carriers of the disease. In order to identify these carriers, it is advised that a guttural pouch wash is performed on horses that have been exposed to strangles, in order to confirm they are clear of disease.
To prevent a strangles outbreak, biosecurity is key. When attending equine events, direct contact and sharing of water sources or equipment between horses should be avoided. Equipment and trailers on the yard should be disinfected regularly. Ideally all new arrivals should be quarantined and monitored for 3 weeks before mixing with the herd. The strangles blood test can be used at this time with one sample taken before movement and one at the end of the quarantine period to identify exposure.