CASE STUDY
EQUINE ENTERIC CORONAVIRUS
IN A CANTERBURY PONY
A case study by JoAnna Faircloth, formerly of Canterbury Equine Clinic, covers the signs, diagnosis and treatment of equine coronavirus in a gelded pony. INTRODUCTION Horses who present with cases of anorexia and concurrent pyrexia without mild signs of abdominal discomfort have been annually documented during the cooler months in Canterbury. These cases have largely been described as mild and self-limiting, and have typically resolved without definitive diagnoses. In recent years these cases have been the topic of discussion, and horses with these conditions are now routinely tested in the Canterbury region to screen for equine coronavirus. CASE HISTORY In July 2019 a 16-year-old, mixed-breed gelded pony was attended to in the field for sudden onset of inappetence and lethargy. The pony had participated in a local competition three days before presentation and a dentist had performed a routine dental check without sedation approximately two days later. There was no recent history of antimicrobial or antiinflammatory administration. The owner had not noted any signs of abdominal discomfort, and all manure in the vicinity was well formed. CLINICAL FINDINGS On presentation the pony was dull and standing off on his own, facing away from feed but was in ideal condition
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(body condition score 4/9). An examination detected a heart rate of 50 beats per minute, a temperature of 39.6˚C and very decreased gastrointestinal sounds. Other findings were unremarkable. The pony was subsequently isolated from other horses on the property and administered a 0.5mg/kg dose of flunixin IV, and blood was collected for screening. Notable bloodwork abnormalities included profound leukopenia of 2.1 x 109/L with a left shift and lymphopenia indicating severe, acute inflammatory demand. A very mild hypomagnesaemia and hypochloraemia were also noted. All other results of the initial blood sample were unremarkable. On being told of the bloodwork findings, the owner revealed that the pony had since stretched out as if to urinate three times, flank watched twice, and been standing close to the water trough. Haematological findings and emerging signs of abdominal discomfort placed impending colitis in the top differential diagnoses. The owner was left to administer flunixin oral paste and an electrolyte paste while monitoring the pony overnight. Approximately 48 hours after the original presentation, the pony developed profound ataxia despite improvements in other clinical signs (heart rate of 46 beats per minute, temperature 36.9˚C).
Although no diarrhoea had yet been noted, a faecal culture swab was taken and sent to SVS Laboratories for processing. An intravenous bolus of 8L Hartmann’s solution was commenced while new bloodwork was processed. A nasogastric tube was passed but no net reflux was obtained, and 250ml of lactulose was administered along with 6L of water with electrolytes. Dimethyl sulfoxide was administered intravenously (1.0g/kg every 24 hours). The second blood sample indicated persistent leukopenia, moderately increased alkaline phosphatase and electrolyte derangements (all mildly to moderately decreased), despite adequate hydration parameters and no outward fluid losses through diarrhoea or reflux. The ataxia was suspected to have been caused by hyperammonaemia secondary to disruption of the gastrointestinal mucosal barrier, although severe or sudden electrolyte derangements can also be responsible for encephalopathic signs. Unfortunately, hyperammonaemia could not be confirmed in this case as the test for blood ammonia level was unavailable on the weekend. The ataxia improved slowly and resolved within 30 hours of initiating fluid therapy of twice-daily IV boluses of 8L Hartmann’s solution per 400kg bodyweight and oral lactulose. The pony’s mucous membranes became injected with a brick-red appearance in the third and fourth days of treatment. The owner noted two small piles of manure that were cow pat consistency in the pony’s pen; this was the only evidence of non-formed manure during the case management. Supportive care consisting of sucralfate (20mg/kg orally, three times a day), lactulose (100ml orally, two to three times a day), oral flunixin paste (0.5mg/kg every 12 hours) and oral electrolyte paste (15ml every 12 hours) was continued for three days, with decreasing amounts of intravenous fluids supplemented with electrolytes as needed and bolused once or twice daily as dictated by daily blood results. The pony also received metronidazole (20mg/kg orally, every 12 hours) for the first three
PHOTO: SUPPLIED
