Strangles is an acute bacterial upper respiratory disease that can affect horses of any breed, sex, or age. However, young horses are most susceptible because of limited prior exposure and immunity. The name “strangles” comes from severe cases of infection when lymph nodes are swollen large enough to cause difficulty in breathing, causing patients to gasp for air. Strangles is caused by the bacteria Streptococcus equi (S. equi). In severe cases affected horses stop eating, have a fever, are depressed, and may have copious amounts of nasal discharge. They may also have a cough or have discharge from the eyes. However, some affected horses have inapparent infections and show no clinical signs or only have swelling in the submandibular lymph nodes. Swelling of these lymph nodes may become firm, hot, and painful and may progress to abscesses. Once the abscess bursts or is lanced by your veterinarian, the horse usually recovers rapidly, with these abscesses healing within a couple of weeks.
In complicated cases of Strangles, several conditions can develop including pneumonia, guttural pouch empyema, “Bastard Strangles”, and Purpura Hemorrhagica (small hemorrhage in the skin). “Bastard Strangles” is the most common secondary complication associated with Strangles. This occurs when bacteria from the submandibular lymph nodes or nasopharynx spread to other parts of the body, leading to abscesses in the retropharyngeal lymph nodes, lungs, and abdomen (belly) . When abscesses develop deep in the body, aggressive and long-term antibiotic therapy is often required.
Is it contagious?
Strangles is highly contagious and spread by direct contact (nasal secretions) from horse to horse or indirectly by exposure to contaminated feed and water buckets, tack, housing, or even clothing and equipment of caretakers and handlers. The bacteria are shed through the nasal and ocular secretions, or from a draining abscess. Horses may carry the bacteria in their upper respiratory tract without showing overt clinical signs and these horses are referred to as “Carriers”. Carriers are an important source of infection to other horses for months to years. The horse’s guttural pouch is a common place where S. equi like to live. Also, these bacteria can live in soil for days, on a fence post for about week or more, and in water for nearly a month. This is why proper cleaning and disinfection are an important part of any horse’s environment, and it is important to isolate new horses before introduction into the herd.
In most infected horses, strangles is easy to diagnose by the presence of clinical signs alone. However, as outbreak progresses, individual animals may not develop the typical signs of a draining abscess. For example, carrier horses may develop and shed bacteria without developing clinical signs, or some horses may develop “bastard strangles” where abscesses form in other parts of the body and clinical signs may not be as obvious. Diagnosis of Strangles is confirmed by isolating and growing S. equi bacteria from pus aspirated from infected lymph nodes, nasal discharge collected on nasal swabs, or from nasopharyngeal washes. In cases where the guttural pouch is infected (Guttural Pouch Empyema), a diagnosis can be made by endoscopic examination of the upper airway and radiographs (X-rays) of the head.
Important Points in Treatment & Management:
Treatment varies with the individual case. Overall, most horses get better with good nursing care and without the use of antibiotics. Once a diagnosis is made and the submandibular abscess is draining, horses should be kept in a warm, dry environment and given highly palatable hay and grain until the disease runs its course. Providing the horse has a good appetite and remains bright and alert, improvement will occur in 1 to 2 weeks. Some horses may require non-steroidal anti-inflammatory drugs (NSAIDS) to help reduce fever, pain, and inflammation, or antibiotics if deemed necessary by the veterinarian. If needed, abscesses can be lanced, and in rare, severe cases, a tracheostomy (opening in the windpipe or trachea) may be required to help the horse breathe. In horses with guttural pouch empyema, the guttural pouches should be flushed to remove pus and debris. Furthermore, in some horses administration of antibiotics in the guttural pouch may kill bacteria that serve as a source of infection to other horses.
As mentioned previously, other complications, such as purpura hemorrhagica, myopathies (muscular disease where the muscle fibers do not function), agalactia (absence of milk production), or infection of other organs such as the liver, lungs, spleen, kidneys, or brain may occur. Purpura hemorrhagica, although rare, is an acute inflammation of blood vessels and capillaries (vasculitis) that occurs as a result of an immune reaction to the S. equi proteins. Purpura hemorrhagica can affect many organs within the body, such as the heart, skeletal muscles, and intestines. Typically, the disease gets its name from the presence of small purple-colored splotches (bleeding) that is found on the body, especially in areas with lighter hair coats and in the mucus membranes of the nose and mouth. Also, severe swelling can be seen in all four limbs and in severe cases, horses may have cardiovascular collapse (heart failure) and death.
The immune condition may extend into the muscles (myopathy) resulting in the regional muscle damage. Mares that become infected may experience agalactia (lack of milk production), which affects nursing foals. In these mares, the foal should be closely monitored to be sure he is nursing and gaining weight. A veterinarian should be consulted for affected mares and their foals.
Once an abscess is opened and drained, most horses recover in 1 to 2 weeks, but could shed bacteria for months to years, acting as a source of infection to others. Once infected, horses develop some immunity against the disease, but it is unknown how long this immunity lasts—it may be only six months, or it may be several years. If complications arise, such as purpura hemorrhagica, aggressive treatment by your veterinarian is required to prevent debilitation and death. If young foals have a severe infection, they may have a reduced growth rate (stunted), but once recovered, seem to progress to normalcy. Prognosis is typically good for horses with Strangles isolated to the submadibular lymph nodes, but the prognosis becomes worse if secondary complications occur.
Prevention of Strangles includes good herd health management, cleanliness, early detection of clinical signs, and quarantine of affected horses. Also, vaccination has been shown to decrease the length and severity of disease on some farms. Proper herd management is of most importance for prevention of Strangles. New horses should not be introduced into the herd until after they have been quarantined for 2 to 4 weeks. Also, identification, isolation, and treatment of carrier horses can be helpful in controlling herd outbreaks. Although not easy, your veterinarian can identify carriers by performing cultures on samples taken from the guttural pouches 4 to 6 weeks after the end of an active infection or on new horses presented to the farm.
Environmental management is critical to control outbreaks on the farm. Infected horses should be identified early in the course of disease and separated from healthy horses. Tack, water buckets, and equipment should be cleaned thoroughly and not shared between horses. Water troughs and barn surfaces should be scrubbed and cleaned regularly and recleaned when an infected horse is discovered. Also, infected horses should not be comingled with healthy horses.
Both intramuscular and intranasal vaccinations are available. You should discuss with your veterinarian the appropriate vaccine and schedule to be used. Vaccines in some instances may prevent disease, but in other situations, they may decrease the length and severity of disease on the farm.
Estimated Cost of Treatment:
Initial cost of treatment would include the costs of an examination, lancing of an abscess (if needed), culture to confirm infection (if needed), and antibiotic or NSAID treatment. Early recognition of disease and isolation of affected horses can reduce costs. If multiple horses are infected or complications occur, then additional treatment may be needed, which will increase costs. Management and cleanliness is paramount in preventing contamination and stopping an outbreak. Your veterinarian should be involved in your herd management plans.
Early recognition is key to minimizing a herd outbreak. If your horse/horses show signs of strangles, immediately isolate the horse and contact your veterinarian so diagnostics and treatment can be initiated to minimize exposure and disease.If you would like to consult a veterinarian about treating or vaccinating your horse for strangles please contact:
Equine Health Studies Program
School of Veterinary Medicine
Louisiana State University
Baton Rouge, LA 70803