Staphyloccocus aureus -associated infarctive purpura haemorrhagica, immune-mediated haemolytic anaemia and myocarditis in a Quarter Horse mare

A 7-year-old Quarter Horse mare was presented for severe left hindlimb oedema and nonweightbearing lameness that was progressive over approximately 48 h. The mare subsequently developed marked and worsening oedema, immune-mediated haemolytic anaemia (IMHA), myositis and myocarditis. The marked oedema, degree of pain and severity of myositis were consistent with infarctive purpura haemorrhagica. Fine needle aspiration of affected tissue resulted in positive bacterial culture of Staphylococcus aureus. Purpura haemorrhagica and associated complications are typically associated with Streptococcal sp. infection or exposure, and have not been previously reported in association with Staphylococcus aureus in the horse. The mare responded favourably to long-term, high-dose corticosteroid therapy, antimicrobials and supportive care.