First description of reactive arthritis secondary to leptospirosis in a dog.

Background: Leptospirosis is a zoonotic bacterial infection that is common worldwide, with a wide spectrum of clinical signs. It commonly infects the kidneys and the liver but can damage a number of organ systems.

Case description: An 18-month-old boxer dog was referred because of reluctance to walk and sickness.

Findings/treatment and outcome: His clinical presentation, including swollen and inflamed joints fulfilled the requirements for a diagnosis of immune-mediated polyarthritis (IMPA). Shortly after, unexpected icterus developed and laboratory signs of hepatic and renal failure were observed. A diagnosis of leptospirosis was reached after observing typical clinical signs, along with a positive microagglutination test. Since the diagnostic molecular test for Leptospira from joint fluids came back negative and also the localization of Leptospira in multiple joints in association with inflammation has never been described in canine patients, an immune-mediated complication seemed most likely. The dog quickly recovered after the administration of ampicillin for 5 days, followed by a two week course of doxycicline.

Conclusion: In human medicine, this case would be considered as a reactive arthritis (ReA), which is mistakenly cited in the current veterinary literature for cases associated with chronic infections. In humans, ReA is described as inflammatory arthritis not directly caused by culture-proven infection of joint tissue but by infection at another site due to a complex interplay of host antimicrobial factors. This case presentation reports for the very first time, a case of canine leptospirosis mimicking an IMPA and fitting the description of ReA in human medicine.