After a young Arizona man died of pneumonic plague last year, a report from Centers for Disease Control and Prevention (CDC) and Arizona scientists yesterday issued a caution to clinicians in areas where plague is endemic. They say to consider it as a possible cause of patients’ severe respiratory and systemic disease if they’ve been exposed to sick animals.

As detailed in a new paper in Morbidity and Mortality Weekly Report, the man who died had occupational exposure to two ill cats, which are especially susceptible to plague. 

The animals may have been how he contracted the bacterium Yersinia pestis, which causes plague, as they had "respiratory symptoms and other signs of systemic illness consistent with pneumonic plague.” However, the cats were euthanized before they could be tested. 

Y pestis in the man's blood and lung tissue

Plague can take several forms, including pneumonic, which is transmitted through inhalation of respiratory droplets and has a nearly 100% case-fatality rate when untreated. The incubation period—the time from exposure to first symptoms—can be as short as one day.

The “young adult male” died eight hours after he was admitted to the hospital, where doctors initially suspected he had hantavirus disease or bacterial pneumonia. Post-mortem testing confirmed Y pestis presence in his blood and lung tissue. It's Arizona’s first pneumonic plague death since 2007.

The most common form of plague is not pneumonic, but bubonic, which causes large, swollen lymph nodes called buboes that are very painful.

Plague endemic in Southwest

While plague has been infecting humans for millennia, the CDC says it was introduced into the United States in 1900 by rat-infested steamships and that the last urban plague epidemic in the country occurred in Los Angeles from 1924 through 1925.

Plague is still found in the western United States, with the CDC showing 502 cases between 1970 and 2023. Over half of these were reported in New Mexico, followed by Colorado and Arizona, which together account for more than a quarter of the remaining infections. 

From 2000 through 2023, the CDC reported 122 cases of plague, including 15 fatalities. 

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