Strangles can be fatal in one percent of cases, but complications are more frequent. In some outbreaks, a small percentage of horses can develop abscesses in other body organs which grow and rupture, a form known as ‘bastard’ strangles. Purpura hemorrhagica (widespread small bleeding along with fluid accumulation (oedema) of the limbs, eye lids and gums) may occur in association with circulating antibody complexes with S. equi M-like protein. The peripheral accumulation of fluid can be so extreme that circulatory failure and death ensue.
Atypical strangles presents as ‘flu-like symptoms, which is a complication that can become persistent on a yard.
Up to 10% of recovered horses may become carriers. This means that they look outwardly healthy but may be able to pass on strangles infection to other horses.