The peripheral blood smear shown here was obtained from a fatal case of plague in a New Mexico resident. Plague was confirmed by isolation of Yersinia pestis from postmortem blood cultures.
Plague is a zoonosis caused by the gram-negative coccobacillus Y pestis.1-4 The disease is transmitted to humans either by flea vectors or, less commonly, by direct contact with plagueinfected animals, which can include dogs, cats, and other carnivores, in addition to the usual rodent and rabbit hosts of the disease. In addition, if a pneumonia secondary to hematogenous spread of Y pestis develops in patients with plague, person-to-person transmission of the disease becomes possible, thereby creating an urgent public health concern.
After the introduction of rat plague to West Coast port cities in the late 19th and early 20th centuries, animal plague entered sylvatic rodent populations throughout the American West.2 The first human plague reported in the