- Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
- Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
- S. equi is more pathogenic and is the cause of strangles with rhinitis, pharyngitis, lymphadenitis
- S. zooepidemicus can cause similar signs to strangles in horses, may accompany COPD
- May cause sinusitis in horses