Overview
Strangles is an infection caused by the bacteria Streptococcus equi subspecies equi (S. equi var. equi). Although horses of any age can be affected, the disease most commonly affects young horses (weanlings and yearlings). It is a highly contagious disease, transmitted by direct contact with infected horses or sub-clinical shedders, or indirectly by contact with objects (water troughs, hoses, feed bunks, pastures, stalls, trailers, tack, grooming equipment, nose wipe cloths or sponges), people (hands and clothing), or insects (contaminated with nasal discharge or pus draining from lymph nodes of infected horses). Streptococcus equi has demonstrated environmental survivability, particularly in water sources and when protected from exposure to direct sunlight and disinfectants, and can be a source of infection for new additions to the herd.
Following natural infection, a carrier state of variable duration may develop and intermittent shedding may occur (this is referred to as sub-clinical shedders).
Clinical signs
Infection by S. equi induces a profound inflammatory response. Clinical signs may include fever, dysphagia or anorexia, respiratory stridor, lymphadenopathy (+/- abscessation) and a copious muco-purulent nasal discharge.
Following the infection, certain individuals may unpredictably develop purpura haemorrhagica, an acute, non-contagious syndrome caused by immune-mediated, generalised vasculitis. Clinical signs develop within 2 to 4 weeks following the infection. Clinical signs may include urticaria with pitting oedema of the limbs, ventral abdomen and head; subcutaneous and petechial haemorrhage; and sloughing of involved tissues. Severe oedema of the head may compromise breathing. Immediate medical attention should be sought for individual horses suspected of having purpura haemorrhagica.
Treatment
Cases are treated symptomatically. NSAIDs are given to reduce the inflammation and fever (and antibiotics to combat the bacterium (penicillin). Horses must be nursed with palatable, easy to swallow, food and rest.
Prevention
Vaccines are available but are expensive and their efficacy and side effects question their usefulness.