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Journal of Veterinary Diagnostic Investigation Vol. 18 Issue 5, 511-513
Copyright © 2006 by the American Association of Veterinary Laboratory Diagnosticians
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Brief Communication

Hepatic yersiniosis in a cougar (Felis concolor)

Michael A. Owston, Ching Ching. Wu and José A. Ramos-Vara1

Correspondence: 1Corresponding Author: Dr. José Ramos-Vara, Animal Disease Diagnostic Laboratory, Purdue University, 406 South University, West Lafayette, IN 47907


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A cougar (Felis concolor) was diagnosed with hepatic yersiniosis by bacterial culture and histopathology. The animal had a 2-week history of anorexia and jaundice before its death. Grossly, the liver exhibited caseo-necrotic foci. Histopathologically, there was necrotizing and suppurative hepatitis, with large numbers of intralesional gram-negative coccobacilli. Additional hepatic lesions included central vein thrombosis, lymphoplasmacytic portal hepatitis, and capsulitis. Yersinia pseudotuberculosis coccobacilli were isolated in pure culture from the hepatic lesions. Because the hepatic lesions in this animal resemble those of other zoonotic diseases, such as plague and tularemia, veterinarians and laboratory personnel who handle samples should take adequate safety precautions. This report is the first to describe the pathology associated with hepatic yersiniosis in a cougar.

Key Words: Cougar • hepatitis • liver • pathology • Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is a gram-negative bacillus that infects a wide range of species, including ruminants, pigs, dogs, domestic cats, and wild animals.1,2,8,13,16,18,19,20 Infections are usually sporadic, but epizootics in wild animals and exotic animal collections have been reported.4,10,11,15,21 Yersiniosis occurs more commonly in the winter, when animals are under stressful conditions.2,4,15,21 Wild rodents and birds may serve as reservoirs for Y. pseudotuberculosis and often have less severe disease compared with domestic species.14,15 There are few published reports of Y. pseudotuberculosis in exotic felids and zoo cats.16,18,20 To the authors' knowledge, this is the first description of Yersinia pseudotuberculosis infection in a cougar.

A 14-year-old male cougar (Felis concolor) died in early March 2005 after a 2-week history of anorexia and jaundice. The animal was housed in an outdoor, large felid rescue facility that had a history of rodent infestation and overpopulation. Animals in this facility were frequently fed raw chicken, beef, and horse meat. Occasionally, the felids received wild animals, usually deer, which had been accidentally killed by cars. A field necropsy was performed, and liver samples were submitted to the Purdue University Animal Disease Diagnostic Laboratory (ADDL) for bacterial culture and histopathology. The liver had numerous, 5–10-mm-diameter coalescing white-tan nodules with caseous centers scattered throughout the hepatic parenchyma (Fig. 1). The hepatic parenchyma was diffusely discolored yellow-green.


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  		Figure 1 Liver, cougar. Multifocal to coalescing areas of necrosis. Bar = 1 cm. Figure 2. Liver; cougar. Photomicrograph showing 2 coalescing necrotic foci. The center contains numerous degenerate leukocytes and cell debris (dark circles). H = nonaffected hepatic parenchyma. HE. Bar = 400 µm.

Figure 3. Liver; cougar. Photomicrograph of a necrotic area. Surrounding the necrotic center (NC) is a band of bacterial microcolonies (B). Leukocytes, mainly neutrophils, surround bacterial colonies. HE. Bar = 50 µm. Inset: Detail of bacterial colonies. Bar = 10 µm.

 
Liver was cultured on blood and MacConkey agars, and incubated at 35°C for 24–48 hours. A pure culture of nonhemolytic, grayish, shiny, discrete, pinpoint colonies were isolated on both types of agar after 24 hours of incubation. A Gram stain was performed and revealed gram-negative rods. The organism was identified as Y. pseudotuberculosis with a biochemical API 20E identification kit (urease positive). No serotyping was attempted on the isolate.

Histopathologically, the hepatic nodules were randomly distributed and unencapsulated (Fig. 2). The centers of these nodules were composed of degenerate leukocytes and cell debris, and were delimited by an irregular band of gram-negative coccobacilli (Fig. 3). Many neutrophils, and fewer macrophages, infiltrated adjacent tissue. Portal regions and central veins had perivascular infiltrates of lymphocytes and plasma cells. Central vein thrombosis was occasionally seen and consisted of aggregates of neutrophils admixed with fibrin. Many leukocytes, primarily neutrophils, were present throughout the hepatic sinusoids. The parenchyma adjacent to areas of necrosis had disorganized hepatic cords. Many hepatocytes, and some macrophages, contained bile pigment, and canaliculi were often plugged with bile. The nature of this pigment was confirmed with a bile acid stain. The hepatic capsule was lined by cuboidal to columnar mesothelial cells and multifocally covered by fibrin.

The hepatic lesions in this cougar were typical of those seen in other animals infected with Y. pseudotuberculosis.12 A diagnosis of hepatic yersiniosis was confirmed by isolation of Y. pseudotuberculosis in pure culture from the liver. The attending veterinarian did not find extrahepatic gross lesions in this cougar at necropsy, and only liver was submitted for bacteriologic and histologic analysis. During the previous month, an additional cougar on the premises had similar clinical signs and nodules within the liver and lungs. However, samples from this animal were not submitted to the ADDL.

The most severe form of Y. pseudotuberculosis infection, described in nonhuman primates, artiodactyls, and edentates is characterized by acute fibrinonecrotizing enteritis and lymphadenitis, with widespread necrosis in liver, spleen, lung, and other organs.3 Systemic infections can be rapidly fatal.12,15,17 However, some animals, including cats, may not develop enteric lesions.13,19 A Siberian tiger with lesions of yersiniosis in peritoneum, liver, and lungs lacked evidence of intestinal disease.16 Enteric lesions in wild cats may only be detected histologically, or characterized merely by marked congestion and hemorrhage without inflammation.16,18

The source and the route of infection in this case was not determined. Domestic animals typically become infected with Y. pseudotuberculosis through the consumption of infected animals or contaminated feed.12 Free-ranging small mammals and birds may be reservoir hosts of Y. pseudotuberculosis and act as a source of infection for deer.8 Of the factors presented in the case history, the increased rodent population or consumption of raw deer may have contributed to the infection of the cougar. Domestic cats have also been suspected as a source of human infection5 but were not known to be on the premises.

Bacterial identification is important for the diagnosis of yersiniosis because the hepatic lesions caused by Y. pseudotuberculosis are similar to lesions of other diseases, including plague (caused by Yersinia pestis) and tularemia (caused by Francisella tularensis).6,9 Furthermore, because Y. pestis and F. tularensis are zoonotic, veterinarians and laboratory personnel handling samples with lesions similar to those in this cougar should take adequate safety precautions.7 It should be stressed that these zoonotic agents may be present in tissues without grossly recognized lesions. Yersiniosis should be included as a differential diagnosis in large felids with necrotizing and purulent hepatitis.


   Acknowledgments
 
The authors appreciate the submission of this case by Dr. Stanley Froderman.


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From the Animal Disease Diagnostic Laboratory and Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, West Lafayette, Indiana 47907. Back


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