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Title: Listeria monocytogenes septicemia in an immunocompromised dog

item PRITCHARD, JESSICA - North Carolina State University
item JACOB, MEGAN - North Carolina State University
item Ward, Todd
item KATHARIOU, SOPHIA - North Carolina State University
item WOOD, MICHAEL - University Of Wisconsin

Submitted to: Veterinary Clinical Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2015
Publication Date: 6/24/2016
Publication URL:
Citation: Pritchard, J.C., Jacob, M.E., Ward, T.J., Parsons, C.T., Kathariou, S., Wood, M.W. 2016. Listeria monocytogenes septicemia in an immunocompromised dog. Veterinary Clinical Pathology. 45(2):254-259.

Interpretive Summary: Listeria monocytogenes is a food-borne bacterium that can cause serious illness in humans and other animals (listeriosis). Certain strains of this pathogen, which are known as serotype 4b strains, are disproportionately responsible for major outbreaks of listeriosis as well as sporadic illness in humans. However, the distribution and diversity of L. monocytogenes strains among non-human animals is less well understood. In this study, a rare case of listeriosis in an immunocompromised dog was documented. The responsible strain of L. monocytogenes was characterized and compared to strains from a wide variety of human and non-human infections. In this case, the L. monocytogenes strain was identified as an epidemic clone 1 type with subtype 1.13_4b_Sw87_EC1, which is responsible for several major outbreaks of listeriosis in humans. We determined that this subtype is relatively rare among isolates from non-human animals (9.7% of 145 isolates tested). Since the route of L. monocytogenes infection is typically via consumption of contaminated foodstuffs and L. monocytogenes has been identified in 16% of raw food pet products, the apparent lack of clinical disease in dogs has led some to speculate that dogs have an inherent resistance to infection. These considerations make this first reported case of L. monocytogenes serotype 4b in a dog a noteworthy observation, which will be of interest to veterinary medicine as well as scientists studying mechanisms of pathogenicity in Listeria monocytogenes.

Technical Abstract: An 11-year-old, male castrated, Boston Terrier was presented to the North Carolina State University College of Veterinary Medicine Small Animal Emergency Service with a 2-day history of progressive ataxia, left-sided head tilt, and anorexia. The dog had previously been diagnosed with chronic lymphoid leukemia and suspected immune-mediated destruction of his bone marrow precursor cells, possibly due to therapy with immunosuppressive dosages of prednisone and azathioprine. During the physical examination, abnormal findings included an increased body temperature and horizontal nystagmus. Diagnostic investigations included a computed tomography (CT) scan, which confirmed bilateral otitis media, and a blood culture, which was positive for Listeria monocytogenes serotype 4b (epidemic clone 1). Upon treatment with ampicillin/sulbactam, enrofloxacin, and minocycline, the dog became normothermic and the neurologic signs improved. L monocytogenes serotype 4b (epidemic clone 1) has been associated with outbreaks of human listeriosis originating from food contamination. Although rare case reports of Listeria spp. infection in dogs exist, an actual infection with the epidemic clone 1 strain has never before been reported in a dog. It should be included in the differential diagnoses in immunocompromised dogs with clinical signs of septicemia.