A 16-month-old, female Labrador mixed-breed dog presented for locomotion problems of 2 months' duration. Distention of multiple joints was noted on physical examination, and analyses of joint fluid were compatible with polyarthritis. Following results of a further workup, the dog was diagnosed with nonerosive, idiopathic, autoimmune-mediated polyarthritis. Oral prednisolone at an immunosuppressive dose (1.5 mg/kg Q 12 H) was started. The dog improved initially but relapsed 3 months after the dose was tapered, and the prednisolone dose was increased again. Shortly thereafter, the dog's condition deteriorated; she presented with painful joints, diarrhea, and hepatomegaly. Further diagnostics were performed, including cholecystocentesis. Listeria monocytogenes was isolated from cultures of this bile sample. Treatment with antibiotics and ursodeoxycholic acid was started, but the dog continued to deteriorate and was euthanized. This was the first reported case of L monocytogenes infection in the gallbladder of a dog. Persistence of this organism in the gallbladder of a pet could constitute a potential zoonotic health hazard.

COMMENTARY: Isolation of L monocytogenes from the gallbladders of humans has been described, but this is the first reported case in a dog. This organism can cause disease and death in humans, although in most healthy adults the infection remains subclinical. In dogs, cases of listeriosis have rarely been reported. In light of the findings in this case, however, it would be interesting to know if there is a population of dogs that are carriers with no clinical signs and whether this dog developed clinical disease subsequent to treatment with prednisolone. This would be an important consideration when starting a pet on immunosuppressive therapy-especially if there are infants or immunosuppressed household members.

Isolation of Listeria monocytogenes from the gallbladder of a dog with liver insufficiency. Marien M, Decostere A, Werbrouck H, et al. FLEMISH VET J 76:352-354, 2008.