The United States now ranks 11th in the world in cases of plague, according to a new survey of the disease.

With 57 cases in a decade, it is far below the hardest-hit countries, Congo with 10,581 and Madagascar with 7,182. Still, it is the only wealthy country on the list; 97 percent of cases are in Africa.

The survey was published by The American Journal of Tropical Medicine and Hygiene.

The Black Death killed a third of Europe in the 14th century, but cases are no longer found there, probably because cities keep rat populations down, said the author, Dr. Thomas Butler, a plague expert at Ross University Medical School in the West Indies. By contrast, in the American Southwest, the bacteria have shifted into rural squirrels and prairie dogs.

Most cases come from flea bites, but in the U.S. a national parks biologist died after inhaling the bacteria while doing a necropsy of a mountain lion, and a 60-year-old geneticist in Chicago died, apparently after being careless with a research strain he believed was safe.