03/05/2025
“Strangles” Disease: Now reportable in the state of Oregon
By Dr. Sabrina Cooper, DVM, AVCA
Streptococcus equi subspecies equi (S. equi) also known as “strangles” disease is a highly infectious, somewhat common disease affecting the entirety of the equine industry in the United States, and is now considered a “reportable” disease in the state of Oregon. This means that your veterinarian is now obligated to report highly suspicious or positive cases to the state veterinarian of Oregon for monitoring and potential management. Previously, it was voluntary to report this disease in Oregon.
Strangles is named such because the hallmark presentation of this disease is significant swelling and abscessation of the lymph nodes within the throat latch area, which can compress the horse’s airway. In some cases it will obstruct the airway completely, causing strangulation/asphyxiation. This requires a life-saving procedure called a tracheotomy to re-establish air flow. Though this is the more classic sign many people think of, often horses display more generalized clinical signs. These signs include fever (temperature above 101.5), inappetence and purulent nasal discharge from one or both nostrils. Some horses may have trouble swallowing and/or have a cough. In severe cases, abscesses may rupture in multiple areas in and around the throat latch, face and head. Some infections may spread to other areas of the body, commonly referred to as “bastard strangles”. Though we typically think of young show horses being the classic patients that get this disease, it can affect horses of any age, gender and discipline. Signs typically develop 3-14 days after exposure, but before most horses are actually contagious. This is why early identification of febrile horses can make it easier to reduce spread by isolating those horses right away. Horses can remain contagious for 2-3 weeks in the majority of cases, but some can remain infectious for 6 weeks after abscesses heal. Additionally, there is a possibility of persistent guttural pouch infection (typically referred to as “chondroids”) which may result in intermittent shedding for years. This means that horses that outwardly appear healthy can be sources of infection for other horses, and is a good reason for testing several or all horses at a barn where there is an outbreak, even in the absence of clinical signs.
Though there are various ways your veterinarian may test for strangles, the gold standard is endoscopy (“scoping”) the guttural pouches for visualization and sampling followed by polymerase chain reaction (PCR) testing for detection of DNA. Other diagnostics that may be performed include full bloodwork, pharyngeal wash, bacterial culture and nasal swabs.
Treatment is supportive in nature, taking care to maintain the horse’s ability to breathe and swallow appropriately. Some cases may require hospitalization. Medications to help reduce fever and decrease inflammation may be prescribed. Antibiotics are not typically recommended for a variety of reasons, such as delay of abscess formation and rupture as well as decreased long-term natural immunity. However, antibiotics may be used in individual, more complicated cases at the discretion of the attending veterinarian.
Strangles is a significant problem causing major economic losses in the equine industry due to the fact that it is very, very contagious and can be shed from positive horses for 6 weeks or more. When a positive case is identified, biosecurity protocols must be established and closely followed to prevent frustrations from new cases popping up at the barn for months, as horses will appear to improve while they can still be shedding S. equi., infecting new horses if they are released from isolation too early. Preventing transmission during travel and showing is imperative. This is important not only for prevention of transmission of strangles, but for other respiratory and gastrointestinal diseases. Good biosecurity practices include not sharing water buckets, not allowing nose to nose contact with other horses and not touching other horses if possible. Do not share bits or other pieces of tack without cleaning and sanitising between horses. Don’t allow horses to smell the manure of other horses. Monitoring temperatures during and after shows is good practice, and a working thermometer is a necessity in any horse owner’s medical kit. Try to have a plan in place to isolate horses with a fever (above 101.5) until your veterinarian can come perform diagnostics. Horses that have had a positive test should not be brought to shows or exposed to other horses for at least 6 weeks after any nasal discharge is noted, or until there has been multiple negative tests performed by your veterinarian. S. equi can remain viable in water for 4-6 weeks. It deteriorates more rapidly (1-3 days) on fencing, soil and manure. New horses at a facility should be isolated from other horses for at least 3 weeks, and have their temperature monitored daily.
There are vaccines available for strangles, though there is no current overarching recommendation regarding vaccination of horses against S. equi. It is best practice to follow the advice of your veterinarian based on your individual horse’s needs.
As of February 2025, both suspect and positive strangles cases are now reportable as “monitored diseases” within the state of Oregon. This means that if your regular or attending veterinarian gets a positive result for strangles or is highly suspicious of the disease, the case must be reported within 15 days to Oregon’s state veterinarian. This allows for identification and control of outbreaks of contagious diseases that are considered to have significant consequences to the diseased animal, economic impacts or zoonotic (can be transmitted to humans) risk. Other diseases that fall into this category of “monitored reportable diseases” include anaplasmosis, equine enteric coronavirus and leptospirosis. Diseases such as rabies, West Nile virus and equine herpesvirus (EHV-1) are considered “immediately reportable” and must be reported to the state veterinarian via phone call on a basis of clinical suspicion as soon as possible. Laboratories that have a positive test for these diseases are also required to report to the state veterinarian. A full list of monitored and immediately reportable diseases in the state of Oregon can be found on the Oregon Department of Agriculture’s website.
AAEP. (2020). AAEP Infectious Disease Guidelines: Strangles.https://aaep.org/wp-content/uploads/2024/03/Strangles_DZ_Guidelines_FINAL_2020.pdf
Boyle, A., Timoney, J., Newton, J., Hines, M., Waller, A., & Buchanan, B. (2018). Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles—Revised Consensus Statement. Journal of Veterinary Internal Medicine, 32(2), 633–647. https://doi.org/10.1111/jvim.15043
ODA : Veterinary Disease Reporting : Veterinarian Resources : State of Oregon. (n.d.). Veterinary Disease Reporting : ODA. https://www.oregon.gov/oda/animal-health-feeds-livestock-id/vet-resources/pages/veterinary-disease-reporting.aspx
Updated guidance published on strangles. (2018, May 15). American Veterinary Medical Association. https://www.avma.org/javma-news/2018-05-15/updated-guidance-published-strangles
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