Strangles is a highly infectious, bacterial upper respiratory disease of equids characterized by abscessation of submandibular and retropharyngeal lymph nodes, with high morbidity and typically low mortality. Transmission occurs via direct contact with infected horses and indirect exposure to contaminated equipment, water sources, and handlers; asymptomatic carriers play an important role in perpetuating outbreaks.
In the United States, strangles became a reportable disease in 2017, though reporting requirements vary by state. Strangles became immediately reportable by veterinarians in Oregon in 2025.
Potential Hosts
Primary hosts include horses, donkeys, and mules. Young horses (especially weanlings and yearlings) may experience more severe disease. Although very rare, human infections have been reported, usually linked to close contact with infected horses.
Clinical Signs
The incubation period for strangles is usually 3 to 8 days but can range up to 14 days. Horses can start shedding bacteria within 2 to 3 days of developing a fever and will continue to shed for 2 to 3 weeks or longer.
Common clinical signs include:
- Fever (103°-106°F), which often precedes other signs by 24-48 hours
- Inappetence
- Depression
- Submandibular/retropharyngeal lymphadenopathy with or without abscessation; retropharyngeal lymph node abscessation often leads to accumulation of pus in the guttural pouches.
- Mucopurulent nasal discharge
- Pharyngitis with dysphagia or anorexia
- Soft, non-productive cough
- Possible upper airway stridor due to pharyngeal compression or neuropraxia induced laryngeal hemiplegia
Potential complications include:
- Metastatic (“bastard”) strangles, particularly involving lymph nodes in the abdomen or less commonly the thorax
- Immune mediated purpura hemorrhagica
-
S. equi-associated myositis
- Retained exudate in the guttural pouches can lead to chondroid formation, chronic inflammation, and the development of a carrier state
Report Strangles
Strangles is an immediately reportable disease in Oregon. If you suspect strangles, please contact the State Veterinarian at 503-986-4711. ODA can assist in getting samples properly submitted and assist with potential biosecurity needs.
Diagnosis & Treatment
Diagnosis of strangles can depend on several factors, including clinical signs and recent vaccination status. Samples may be taken as nasal swabs, aspirated/swabbed abscesses, or nasopharyngeal or guttural pouch washes. Bacterial culture can detect
S. equi when present, but this method may be limited during early phases of infection or with intermittent shedding in carriers. Whereas PCR is more sensitive, has a more rapid turnaround time, and may be more helpful identifying carriers, it does not differentiate between live and dead bacteria. In horses recently given an intranasal live attenuated strangles vaccine, PCR may detect shed vaccine DNA (for up to 2-3 weeks), while culture usually stays negative because the attenuated strain rarely grows under standard culture conditions. Serologic testing also may be used for various reasons including detection of previous infection, strangles-associated complications, or to guide vaccination decisions.
Treatment usually involves:
- Supportive care: rest, hydration, anti-inflammatories/analgesics as indicated, and warm compresses to facilitate abscess maturation and drainage.
- Antibiotics generally are reserved for complicated or severe cases as routine use can delay abscess maturation and may blunt development of protective immunity.
Prevention
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Biosecurity:
- Isolate new arrivals, horses that may have been exposed during travel, and sick horses for 14 to 21 days.
- Hand hygiene, clean clothing, and changing gloves between horses are critical to preventing indirect transmission within a facility.
- Manage carriers and convalescents carefully, recognizing their role in outbreak persistence; consider guttural pouch evaluation in recurrent facility cases.
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Vaccination:
- Follow vaccination guidelines of the American Association of Equine Practitioners (AAEP): strangles vaccines are
risk-based and may be recommended for herds with endemic pressure or high exposure risk; avoid vaccinating exposed or actively infected horses due to risk of increased adverse events.
- Monitor for immune mediated reactions; titers may help identify individuals at higher risk prior to vaccination.
-
Disinfection:
- Thoroughly clean and disinfect stalls, wash racks, fencing, trailers, and any surface/fomites that may have been contaminated with nasal discharge or draining abscess material.
- Ensure adequate drying of equipment and housing areas since S. equi can persist for weeks in damp or shaded environments.
Resources
ODA Resources
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