Strangles is an infectious and highly contagious respiratory disease of the upper respiratory tract seen mainly in young horses. It is caused by the bacterium Streptococcus equi and is spread by direct contact with the pus and nasal discharge. The disease can be actively spread to other horses for the period of 3 to 10 days following the infection.
remains one of the most commonly diagnosed and important infectious diseases of horses world-wide. Strangles infection is extremely contagious. Contaminated tack, feeding utensils, water tubs and bedding are all potent sources of infection. The organism gains entry to the body at the back of the throat and rapidly settles in the tonsils and lymph nodes. From there it spreads to the lymph glands of the head and neck, and causes the swelling and abcess formation so typical of the disease. Most horses recover with no complications, and some 70% develop life-long immunity. It is thought that other 30% become carriers of the disease.
Affected animals have a fever, a nasal discharge at first watery then mucous, and poor appetite. Head carriage may be stiffer than normal, swallowing may be difficult and a soft cough heard. Lymph nodes beneath the lower jaw enlarge. These swelling can impair breathing, (hence "strangles") by compressing the airways.
Usually horses recover rapidly once the swelling ruptures. Occasionally lymph nodes fail to filter the infection, which spreads to other systems (bastard strangles) producing abcesses, aspiration pneumonia and pleuritis, and even brain damage by inducing metastatic brain abscesses.
Diagnosis is made based on clinical signs and confirmed on bacteriological culture, since the presence of swollen lymph nodes under the jaw can indicate many other respiratory diseases (Equine Herpesvirus etc.).
Recent findings suggest that S. equi meningoencephalomyelitis should be considered for foals with neurologic signs that have a history of strangles or exposure to affected horses.
The nostrils should be cleaned, hot pads applied to the swelling, and soft, easily swallowed feed provided. Strict hygienic measures should be observed as the organism can be transmitted on hands and clothes. Treatment of choice is administration of potassium penicillin and fluids. Antibiotics are used in severe cases, particularly when the infection spreads to lungs and abdomen.
Prevention is possible. In a closed herd situation, new arrivals should be isolated for 2 weeks. Since the organism can be shed from draining abscesses for up to 4 weeks and can remain viable for another month or longer, affected horses should be isolated. In-contact animals should be quarantined and observed for signs. However, current antibiotic therapy is often ineffective and thus recent attention has focused on vaccine development.