Strangles

Strangles, a highly contagious upper respiratory disease of equids, is caused by the gram-positive β-hemolytic bacterium Streptococcus equi ssp. equi. 

This disease was first reported in the 13th century and can be found worldwide.

Although rare, Streptococcus equi ssp. equi infections have caused bacteremia and meningitis in humans and fatal pneumonia in a camel. 

Positive cases of strangles in equids must be reported to the State Veterinarian’s Office.

To report strangles or other reportable diseases, call (850) 410-0900 from 8 a.m. to 5 p.m., Monday through Friday. For after-hours reporting, call 1-800-342-5869 or email RAD@FDACS.gov.

Transmission

The organism Streptococcus equi ssp. equi can be transmitted via direct contact with nasal or ocular secretions or lymph node discharge from infected horses or via indirect exposure to contaminated trailers, stalls, riding equipment, buckets, halters, lead ropes, brushes, clothing, etc.

Clinical Signs

The incubation period typically ranges between two and six days but may last up to 14 days. 

Classic symptoms may include fever (103 degrees F or higher), mucopurulent nasal discharge, lymphadenopathy (+/- abscessation), general malaise, pharyngitis, dysphagia, upper airway stridor and respiratory distress. 

Clinical signs are often age-related, with older horses exhibiting milder symptoms of shorter duration.

Diagnosis

Diagnosis of Streptococcus equi ssp. equi infection is mainly accomplished by culturing nasal swabs, nasal washes, or pus aspirated from abscesses. 

Nasal washes generally yield better results than nasal swabs due to sampling of a greater surface area.  

PCR (polymerase chain reaction) can be used as a quick adjunct to a culture and is three times more sensitive than culture. 

The most reliable diagnosis is achieved when PCR results are confirmed with culture. 

PCR can be very useful for detecting asymptomatic carriers, determining infection status prior to transport or entry into a new herd and for establishing whether treatment was successful.

Treatment

There are many different opinions regarding the appropriate treatment of horses with strangles.

Check with your veterinarian to determine which treatment is right for your horse.

Treatment often consists of rest, water, moistened food and a clean, dry stall, which is generally sufficient for most cases. 

Nonsteroidal anti-inflammatory medications such as flunixin meglumine or phenylbutazone can also be administered to reduce pain, swelling around abscesses, and fever. 

Use of antibiotics remains controversial, but penicillin is the drug of choice. 

Streptococcus equi ssp. equi also exhibits sensitivity to potentiated sulfonamides and oxytetracycline. 

In the face of an outbreak, horses with early clinical signs may benefit from three to five days of antibiotic therapy to arrest progression of the disease. However, these horses will be highly susceptible to reinfection and should not be continually exposed to other infected horses. 

Antibiotic therapy is contraindicated in horses with external lymphadenopathy because it prolongs the enlargement and rupture of abscesses. In these cases, treatment should focus on hastening the maturation of abscesses through hot-packing and application of drawing salves such as Ichthammol. In situations where abscesses do not progress, surgical drainage may be warranted.

Supportive therapy and treatment with antibiotics are indicated in horses that are systemically ill or that develop serious complications such as dysphagia, aspiration pneumonia or respiratory distress.

Prevention and Control

Vaccines for strangles include an attenuated live, intranasal Streptococcus equi ssp. equi product and a killed, protein-rich acid and enzyme product that can be given intramuscularly. 

Neither of the strangles vaccines currently available guarantees prevention, and the attenuated live vaccines have been associated with adverse reactions. 

The level of immunity induced by vaccines is lower than that produced during recovery from strangles due to failure to stimulate mucosal antibodies. 

Check with your veterinarian to determine which vaccine is right for your horse.

Establishing high standards of management practices can be an effective means of prevention. 

Horses being introduced to a new herd should be isolated for a minimum of three weeks and should be monitored at least twice daily for evidence of fever spikes, nasal discharge, lymph node enlargement and dyspnea.

If possible, new additions should be screened for Streptococcus equi ssp. equi through PCR and culture of nasal swabs or nasal washes prior to commingling. 

Biosecurity measures should be implemented and maintained to avoid indirect transmission between quarantined horses and resident horses. 

Control measures during an actual outbreak include immediate quarantine of suspected and confirmed cases, restricting movement of horses on and off property until quarantine release, disease surveillance among exposed horses (observing for clinical signs, monitoring temperatures, PCR testing, etc.), implementing strict biosecurity protocols, maintaining isolation of affected horses for a minimum of 21 days after resolution of clinical signs (due to possible nasal shedding for two to three weeks), and retesting infected horses prior to quarantine release.

Regulatory Considerations

Strangles is a reportable disease in the state of Florida due to its highly contagious nature among horses and its zoonotic potential.

Quarantines may be issued on premises affected by strangles.

Although human cases are rare, it is recommended that immune-compromised individuals take precautions to avoid exposure to horses infected with Streptococcus equi ssp. equi.