Strangles (also referred to as “distemper”) is a highly contagious disease of horses that is caused by the bacteria, Streptococcus equi (S. equi). While the disease primarily affects young horses, any age equid may be infected. The infection is transmitted via direct contact with infected horses or sub-clinical carriers, or indirectly from waterers, feeders, pastures vectors (flies), tack and grooming equipment contaminated with nasal discharge or pus from the abscesses of infected horses.
As stated above, a percentage of outbreaks begin without a known source. This is usually derived from a horse incubating the disease or an asymptomatic carrier horse which is shedding the bacteria without having outward clinical signs. Examples of asymptomatic shedders include horses that have recently recovered from the disease but are still shedding the bacteria in the nasal secretions (this can occur for up to 6 weeks following clinical recovery), sub-clinical long-term carriers (typhoid Mary) which include horses harboring the organism in the guttural pouches.
The first clinical signs of infection with Streptococcus equi include rapid onset fever between 102-104 F, mucoid nasal discharge and swelling in the regional lymph nodes of the head, most commonly the submandibular lymph nodes between the lower jaw bones. The incubation period for the disease is 3-14 days. The fever is usually first, followed in 2-3 days by the nasal discharge and lymph node swelling. The lymph nodes will ultimately abscess and rupture if not lanced first. Other symptoms associated with the disease include depression, anorexia, labored breathing and dysphagia (difficulty eating).
Associated complications to the disease include purpura hemorrhagica (vasculitis) and metastatic abscess formation (bastard strangles).
The diagnosis of the disease is made based on the history and clinical signs and confirmed with nasal PCR tests and culture of the organism from nasal discharge or abscess exudates (pus).
Treatment is initially directed at decreasing the fever and managing the general depression. This is to combat secondary colic and dehydration. The lymph node swelling is hot-packed to promote maturation to facilitate abscess lancing. Following lancing of the abscess they are flushed daily and often packed. The goal is to promote healing from the inside out. Fly control and eliminating exposure to other non-infected horses is a must. Antimicrobial therapy is controversial and is implemented at the discretion of the veterinarian on a case by case basis.
Control and prevention is directed at strict farm management. Affected horses should be quarantined at least 100 feet from the general population. They should be fed and handled after and separately from the general population. All movement of horses in and out of the ranch should be halted. When dealing with the infected population the handler should wear gloves, protective covering, and utilize foot bathes. Strict fly control should be exercised. Frequent removal of fecal and bedding material (to an isolated area or bagged), premise spraying for flies and use of fly sprays and ointments such as SWAT should be utilized. Infected animals should be isolated from the general population for 4 weeks to minimize shedding of the organism. In addition, new arrivals to the farm should be isolated in a quarantine area for 4 weeks.
Vaccines are available for the condition. Both intra-muscular injectable vaccines as well as intra-nasal vaccines are available. Neither form of the vaccine gives 100% immunity. The expected immunity from either the vaccine or the disease is estimated at 1 year.
In review, strangles is a highly contagious disease with a very high morbidity (high percentage of infection in a population) and low mortality (low death rate). Horses can transmit the disease for weeks following the disease, even when no longer showing signs of the disease. The clinical signs include high fevers, nasal discharge and enlarged lymph nodes that progress to lymph node abscessation. Affected horses should be confined to isolation during treatment and remain in isolation for up to 4 weeks. Vaccination is available but is not a substitute for good farm management practices.
If you have any questions regarding strangles, please don’t hesitate to contact our office.