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EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2019) 31 (5) 230-235 doi: 10.1111/eve.12855


Case Report


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


A. C. Trimble* , K. M. Delph, L. A. Beard and E. G. Davis


Kansas State University Veterinary Health Center, Manhattan, Kansas, USA. *Corresponding author email: trimblea87@vet.k-state.edu Keywords: equine; purpura haemorrhagica; immune-mediated haemolytic anaemia; myocarditis; Staphylococcus aureus


Summary 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.


Introduction


Purpura haemorrhagica is a relatively rare condition of aseptic necrotising vasculitis observed in horses. Clinical signs most commonly reported include: asymmetric, well- demarcated subcutaneous oedema of all four limbs, mucous membrane petechiation, fever, lethargy, anorexia, weight loss, reluctance to move and colic (Pusterla et al. 2003; Kaese et al. 2005; Boyle 2016). Clinical pathological changes often include anaemia, leukocytosis, neutrophilia, hyperfibrinogenaemia, moderate elevations in creatine kinase (CK), aspartate aminotransferase (AST) and globulins. In some cases, azotaemia may be present and could be consistent with primary renal injury secondary to pigment- associated nephropathy in severely affected individuals (Pusterla et al. 2003; Kaese et al. 2005). Histopathology of skin biopsy samples from affected individuals is characterised by leukocytoclastic vasculitis with neutrophil infiltration (Pusterla et al. 2003). Some horses exposed to Streptococcus equi (S. equi) may suffer from immune-mediated complications such as myositis with progressive muscle atrophy (Lewis et al. 2007; Waller 2014; Valberg 2015; Boyle 2016), infarctive purpura haemorrhagica affecting muscles and organs including the gastrointestinal tract and lungs, immune- mediated haemolytic anaemia (IMHA), immune-mediated thrombocytopenia (IMTP) and myocarditis (Pusterla et al. 2003; Kaese et al. 2005). Most frequently, purpura haemorrhagica is associated


with S. equi exposure or infection (Timoney 1993; Pusterla et al. 2003; Kaese et al. 2005; Duffee et al. 2015; Valberg


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2015; Boyle 2016). Notably, in both human and equine patients, purpura has also been associated with other pathogens, medications and vaccines (Michel et al. 1992; Durward-Akhurst and Valberg 2017). Pusterla et al. (2003) reported that among 53 horses diagnosed with purpura haemorrhagica, 17 had confirmed exposure or infection with


S. equi, nine suffered from Corynebacterium


pseudotuberculosis infection, five had respiratory infection of unknown aetiology, and two had septic wounds, while 15 had no recent history of viral or bacterial infections or exposure to medications. Although uncommon, equine influenza has also been reported to be associated with purpura haemorrhagica in horses (Uppal et al. 1990). Similar to horses, human patients with Henoch- Sch€


haemorrhagica in humans) most commonly develop disease secondary to streptococcal infection, although multiple reports document associations with Staphylococcal sp. infection (Hirayama et al. 1998; Yoh et al. 2000; Eftychiou et al. 2006; Temkiatvises et al. 2008;Audemard-Verger et al. 2015; Maliske et al. 2015). There are no previous reports of equine purpura


haemorrhagica developing secondary to Staphylococcus aureus; however, the current report describes the aforementioned in a Quarter Horse mare with positive bacterial culture and clinical findings consistent with purpura haemorrhagica. In addition to characteristic clinical signs of oedema and pain of the affected limb, this mare also developed severe IMHA and myocarditis.


Case presentation


A 7-year-old, 500 kg Quarter Horse mare was presented to the Kansas State University Veterinary Health Center (KSU- VHC) for progressive, proximal left hindlimb swelling of approximately 48 h duration. Septic cellulitis was suspected by the referring veterinarian, and the mare was therefore treated with ceftiofur crystalline free acid (Excede1) once intramuscularly at 6.6 mg/kg bwt and phenylbutazone2 orally at a dose of 4 mg/kg bwt twice daily. Historically, the mare was raised by the owner and had


no illness, surgery or trauma in the previous year. Deworming with ivermectin and vaccinations that included eastern/ western equine encephalomyelitis, West Nile virus, tetanus, rabies, equine herpesviruses 1 and 4, and equine influenza were administered 6 and 8 weeks previously, respectively. The mare was maintained on pasture with other horses that were healthy the morning of presentation. The herd had no


onlein (purpura


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