Pneumonic Plague Transmission from a Sick Dog — and Possibly from a Human

Plague, caused by Yersinia pestis, is endemic in the western U.S. (New Mexico, Arizona, Colorado, and California). Most commonly, it is transmitted — via fleabites — from rodents such as prairie dogs. The three most common forms are bubonic, septicemic, and pneumonic, with the last transmissible from human to human. Dogs may be infected, but disease is usually asymptomatic or mild.

Four people in Colorado received a diagnosis of pneumonic plague in June/July 2014. The first (Patient A) developed fever and cough shortly after his dog died of pneumonia. A bacterial isolate from this patient was erroneously identified by an automated system as Pseudomonas luteola. When the patient's pneumonia worsened, further testing revealed Y. pestis. The pa…