On Saturday, Feb. 18, the Nevada Department of Agriculture (NDA) began receiving accounts of horses exposed to equine herpes virus type 4 (EHV-4) and Streptococcus equi bacterial infection (also known as strangles or equine distemper). Both diseases are highly contagious among horses, and strangles is listed on the National List of Reportable Animal Diseases.

Strangles is the common name for a bacterial infection affecting horses. The disease is caused by the bacteria Streptococcus (S. equi). The name strangles came about because affected horses sometimes are suffocated by enlarged lymph nodes that obstruct the airway. The organism has been around for hundreds of years and is found throughout the entire United States as well as Europe. Because the bacterium is highly contagious, large outbreaks periodically occur.

Strangles is an intracellular bacterium. This means that the bacteria like to live and multiply within cells. It particularly likes cells associated with lymph nodes. Lymph nodes are important elements of the immune system and are found throughout the body. These bacterial cells lives within lymphocytes and will often set up an infection in the lymph nodes around the head and throat. It can survive for long periods of time out of the body and horses can become infected with the bacteria months after an infection had been noted on a specific property. The bacteria is transmitted by inhalation of dust and respiratory secretions that contain the organism.

The incubation period of strangles is 3–14 days, and the first sign of infection is fever (103°–106°F). Within 24–48 hours of the initial fever spike, the horse will exhibit signs typical of strangles, including mucus-like nasal discharge, depression, and enlarged lymph nodes located beneath the lower jaw. Horses will have difficulty swallowing, respiratory noise, and extended head and neck. Younger horses tend to develop severe lymph node abscessation/enlargements that subsequently rupture and drain. Older horses tend to show a milder form of the disease characterized by nasal discharge, small abscesses and rapid resolution of the infection.

Transmission of the disease occurs when direct or indirect transfer of bacteria occurs via nasal discharge or lymph node drainage of infected horses to susceptible horses. Horses with either type of discharge are an important source of new infections in horses. Direct transmission refers to when horses have nose-to-nose contact. Indirect transmission occurs via contaminated stalls, water sources, feed utensils, and tack as well as clothing and equipment of handlers, farriers and veterinarians.

Diagnosis of strangles is by culture of nasal swabs, nasal washes or from pus aspirated from abscesses. PCR (DNA test) can also be performed to detect the presence of S. equi.

Treatment of strangles depends upon the stage of the disease. The main treatment for horses is supportive care. Fevers are controlled by anti-inflammatory drugs. Enlarged lymph nodes are hot packed daily to expedite maturation and drainage of abscesses. Penicillin (antibiotic) is used in some horses depending upon where the horse is in the course of the disease. Treatment with penicillin in horses that have enlarged lymph nodes will decrease clinical signs of the disease, but once the penicillin is stopped the disease is maintained until the lymph nodes go on to abscess and drain. Usually penicillin is reserved for horses that have a fever but show no signs of lymph nodes enlargement or in complicated cases where the life of the horses is threatened.

Currently, two types of S. equi vaccines exist in the USA. One is a bacterial cell wall extract vaccine. This vaccine is given intramuscularly (IM) or subcutaneously. Initially horses need two doses 2-3 weeks apart and then yearly boosters. Horses that have had strangles within the year or horses that are showing signs of the disease should not be vaccinated. It takes 2 weeks for immunity to build post vaccination with the IM vaccine. The second vaccine is a live S. equi bacterium given intranasally. The vaccine is essentially a weakened form of the bacterium that causes very mild disease (usually no clinical signs), and thus stimulates immunity. It is given initially in 2 doses 2-3 weeks apart and then boostered annually. It is recommended to not use this vaccine in an outbreak situation unless given to a horse that has no known contact with exposed or infected horses.

It should be noted that both of the vaccines can also cause the complications listed above as well as abscesses in the neck or rump where the vaccine was given.

The NDA’s state veterinarian, Dr. JJ Goicoechea, DVM, recommends, “All horse owners should consult with their veterinarian to ensure vaccinations are current,” Goicoechea added. “If you suspect your horse may be exhibiting signs of illness, contact your veterinarian and do not allow contact with other horses.”

Per Nevada Revised Statute (NRS) Chapter 571.160, any animal owner or practicing veterinarian who has knowledge of an infected animal, shall immediately notify the state quarantine officer (NDA Director Jim Barbee). A list of reportable diseases can be found at agri.nv.gov.



Sources:

Everything you ever wanted to know about Strangles, Jenifer R Gold, DVM, Diplomate ACVIM

Dozens of Horses Statewide wi9th Reported Disease Exposure, Nevada Department of Agriculture, News Release, February 22, 2017.