From Scientific America
People may think of the plague as a disease from centuries past, but more than 1,000 people in the United States have become infected with plague in the last 100 years, according to a new study.
In the U.S., between 1900 and 1925, there were nearly 500 cases of plague, mainly in port cities such as those in California and Louisiana. The disease was brought to the United States by infected rats who found their way aboard steamships, the researchers said. (The very first case of plague occurred in San Francisco’s Chinatown.)
In this early period, there were several outbreaks of pneumonic plague, the only form of plague that can be transmitted from person to person. Most cases, however, were of bubonic plague, which is most often transmitted by fleabites.
Then, between 1926 and 1964, there were only 42 cases of plague (about one case per year). These cases occurred mostly inland, in California and New Mexico, with a few cases in Arizona, Colorado, Idaho, Oregon and Utah.
But cases rose again between 1965 and 2012, when there were 468 reported cases of plague—typically about eight cases per year, mostly in the Southwest.
This rise suggests that Yersinia pestis has become “fully entrenched” in disease transmission cycles in animals in the West, the researchers said.