Streptococcus equi Infectious Disease Guidelines

The upper respiratory disease commonly referred to as strangles is caused by Streptococcus equi subsp equi. Less commonly, the bacteria affect lymph nodes in the thorax and/or abdomen, causing a syndrome known as metastatic or “bastard strangles”.

Clinical signs are age and immune status dependent, with older horses typically exhibiting milder signs of shorter duration. Vaccinated animals may show mild signs.  Every horse is at risk of disease when challenged with substantial pathogen dose and frequency.