What is Strangles? Strangles is a contagious bacterial infection in horses caused by the bacteria Streptococcus equi subspecies equi.  Occasionally the related bacteria called Streptococcus equi subspecies zooepidemicus causes clinical signs in horses similar to those seen in Strangles, although this second bacteria is also found on healthy, normal horses and in other species like cows.

Clinical Signs. Clinical signs of Strangles include fever, yellow or green nasal discharge, abscessed lymph nodes around the throat, and occasionally more severe internal illness and death in horses. 

Transmission Between Horses. The bacteria can spread  easily through a stable.  It is transmitted by direct nose-to-nose contact between horses.  Healthy horses may become infected when they lick or chew fencing or rails contaminated by the nasal and abscess discharge from sick horses.   Flies help spread the bacteria by landing on the nasal discharge or open abscesses of a sick horse then landing on the nose of a healthy horse.  People may spread the bacteria on their hands by touching sick horses and then healthy horses.  People also spread the infection between horses when they use the same buckets, grooming material, and other equipment for both healthy and sick horses. Strangles can be introduced into a stable when new horses carrying the infection are brought into the stable.  Resident horses that travel outside the stable for training or events may bring the infection back home when they return.

Transmission to Humans. In rare cases, humans have contracted infections from the bacteria that cause Strangles.  To prevent human infection, people caring for horses with Strangles should avoid getting any nasal or abscess discharge from the horse on their eyes, nose, or mouth.  The should also wear disposable gloves while working with the horse, avoid touching their face, and should wash their hands thoroughly when finished. 

Diagnosis and Treatment.  Strangles cases should always be seen by a veterinarian.   The veterinarian may perform a culture to diagnose the bacteria,  may prescribe antibiotics, and will likely recommends frequent cleaning of abscesses.  The sides and edges of the stall should be cleaned and disinfected daily to prevent dried nasal and abscess discharge from accumulating.  Any gauze or other materials used in cleaning abscesses and nasal discharge must be disposed of in a covered or sealed trash receptacle, to prevent flies from landing on it. The infected horse should be isolated from healthy horses.  Horses that recover completely are usually immune to the bacteria for many years afterward.  However, up to 10% of horses that appear to be recovered may still carry the bacteria and spread it to others for prolonged periods (i.e. become "carriers").

Prevention. Stables should have a designated quarantine area in which new arrivals are placed for 3 weeks and observed for symptoms.  This quarantine area needs to have its own, dedicated equipment for caring for the horses (buckets, brushes, feed area, equipment for mucking out) so that contaminated equipment is not used on healthy horses in the rest of the stable.   Ideally new horses are screened for Strangles.  Vaccines against strangles are available and can help greatly in reducing the severity of illness, should the horse get infected.  In certain cases, vaccines against strangles may be contraindicated.  Consult with your horse's veterinarian to decide if vaccination against strangles is needed for your horse.

Strangles in Los Angeles County. Three Strangles outbreaks were reported in Los Angeles County between 2004-2008.  It is likely to be underreported. 

Strangles Myths. Misinformation about strangles has been encountered during outbreak investigations.  Common examples include: the belief that Strangles infections are never serious, the belief that Strangles infections are unavoidable, and the belief that humans cannot become infected with Strangles.  All  are false.   Deaths of horses have been reported in at least 2 Strangles outbreaks in Los Angeles County. Proper stable management and sanitation can reduce the risk of Strangles infections considerably.  Human infections with Strangles, although not common, do occur.

Reporting. Outbreaks of strangles are reportable in Los Angeles County. Click here to download the form for reporting strangles in horses. Email the completed form to vet@ph.lacounty.gov or fax to 213-481-2375.

More Information
American Association of Equine Practitioner's webpage on Strangles

American College of Veterinary Internal Medicine's 2018 Consensus Statement on Strangles

American College of Veterinary Internal Medicine's 2005 Consensus Statement on Strangles

Equine Strangles FAQ - English & Spanish 2023

Equine Strangles FAQ  - English & Spanish - Poster 2023

Equine Strangles FAQ 2007

Outbreak of Strangles in the Antelope Valley - 2007

Equine Strangles Information 2005

Links to scientific articles on human cases
2003 - Streptococcus equi subspecies equi (Lancefield group C) meningitis in a child
2006 - Post streptococcal acute glomerulonephritis secondary to sporadic Streptococcus equi infection
2004 - Primary purulent pericarditis due to group C Streptococcus

                                        Last updated: October 11, 2023