Histopathology of experimental plague in cats

Formalin-fixed paraffin-embedded archival tissues of seven adult cats of bo th sexes that died after being experimentally infected with Yersinia pestis were examined light microscopically to characterize the lesions. The cats were exposed in two groups using two routes of infection: ingestion of Y. p estis-infected rodent or a subcutaneous injection of Y. pestis to simulate a flea bite. Immunohistochemistry was performed on tissues from all organ s ystems from a representative cat from each group to determine the distribut ion of Y. pestis bacilli during infection. In all seven cats, bubonic plagu e lesions were seen. The lesions of pneumonic plague were present in two ca ts. Septicemic plague was confirmed in all seven cats by bacteriologic cult ure. Aggregations of bacteria were seen in lymphoid tissue in all cats and in lung tissues from the two cats with pneumonic plague. The most consisten t histologic finding was necrosuppurative inflammation in the lymph nodes. Invariably, Y. pestis bacteria were present in large numbers at affected si tes. Orally infected cats had more numerous lesions in the lymph nodes of t he head and neck regions. These experimentally induced cases of feline plag ue document that cats are unique among carnivores in exhibiting bubonic, pn eumonic, and septicemic plague following exposure to Y. pestis. The lesions of the orally infected cats were consistent with those previously describe d for naturally occurring Y. pestis infections in cats and corroborate the contention that cats most commonly contract plague by eating Y. pestis-infe cted rodents and not via flea bite. The histopathology of Y, pestis disease in these cats is comparable to that described for human plague.