Yersinia pestis infection (plague) in cats: Histopathological and macrophage infection studies

Yersinia pestis is the agent that causes a potentially lethal infection in humans known as plague. This Gram-negative bacterium exists in certain rural ecological niches worldwide where it is maintained in a complex cycle involving resistant rodents and their fleas. From these endemic foci, Y. pestis may radiate, causing disease in many other susceptible rodents or incidental epizootic mammalian species, including humans and domestic cats. The virulence and pathology of Y. pestis infection in rodent hosts is possibly different from the disease in humans and cats. Plague infected cats are a significant zoonotic link for human cases. Interestingly, cats are rare among carnivores in their susceptibility to plague. Most other carnivores tested mount a sufficient immune response to avoid clinical symptoms. The purpose of the studies presented here was to examine plague infection in the domestic cat, a new and relevant animal system.; Investigations were conducted to characterize the histopathology of plague in cats. Formalin-fixed tissues from 7 cats with experimental plague infections were used. Immunohistochemistry was developed and performed to specifically confirm the distribution and extent of the Y. pestis in tissues from all major organ systems. The most consistent histologic finding was necrosupparative inflammation in the lymph nodes. Invariably, Y. pestis was present in large numbers in all affected sites. The histopathology of Y. pestis disease in these cats is comparable to that described for human plague.; In vitro investigations were performed using primary peripheral blood monocyte derived feline macrophages to determine the role of this innate immune cell during the initial phase of plague infection. Macrophage cultures were infected with Y. pestis strain KIM5 and evaluated at five time points thereafter up to seven hours post infection. Comparable studies were performed using Escherichia coli HB101. It was found that Y. pestis survives within cultured feline macrophages over the first five hours following infection, while E. coli is largely destroyed. This work supports the hypothesis that failure of the macrophage to contain the plague infection during the early stages of infection leads to an overwhelming susceptibility in cats.