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.

The researchers examined cases of plague in the United States from 1900 to 2012. During that time period, there were 1,006 cases of plague, in 18 states, the study found. Patients ranged in age from less than 1 year old to 94.

Plague is caused by the bacterium Yersinia pestis, and is carried by animals such as rats, ground squirrels and prairie dogs, and their fleas. The disease is known for killing millions of people in Europe in the 1300s, in a pandemic called the Black Death.

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…. (read more)

