Vaccine strain Listeria monocytogenes abscess in a dog: a case report

Background Listeria monocytogenes is a promising therapeutic vaccine vector for cancer immunotherapy. Although highly attenuated, three cases of systemic listeriosis have been reported in people following treatment with Listeria-based therapeutic vaccines. This complication has thus far not been reported in canine patients. Case presentation A dog previously diagnosed with osteoblastic osteosarcoma was presented for care following administration of three doses of the Canine Osteosarcoma Vaccine-Live Listeria Vector. On routine staging chest radiographs, mild sternal lymphadenopathy and a right caudoventral thoracic mass effect were noted. Further evaluation of the mass effect with computed tomography and ultrasound revealed a cavitated mass associated with the 7th right rib. Aspirates of the mass cultured positive for Listeria monocytogenes. The mass and associated ribs were surgically removed. Histopathology was consistent with metastatic osteoblastic osteosarcoma. Treatment was continued with doxorubicin chemotherapy and at the time of publication, the dog was alive over 1 year following diagnosis with no evidence of further disease progression. Genotyping of the abscess-derived L. monocytogenes was consistent with the vaccine strain. Conclusions This case represents the first veterinary case to describe development of a Listeria abscess following administration of a Listeria-based therapeutic vaccine.