Leprosy is often thought to be an ancient disease, but leprosy-causing bacteria continue to infect people in the southern United States, including in Florida, where nine people have been diagnosed with the disease so far this year.

What's to blame? It could be the nine-banded armadillo (Dasypus novemcinctus) that roams wild across much of the Southeast, experts say.

"Keep your distance from armadillos," said Dr. William Schaffner, an infectious-disease specialist at the Vanderbilt University Medical Center in Nashville, Tennessee, who wasn't involved in the Florida cases. "Don't play with them, don't eat them and don't keep them as pets." [10 Deadly Diseases That Hopped Across Species]

The cause of the Florida cases is still unknown. Researchers know that armadillos can transmit the disease to humans, but the Florida Department of Health hasn't tested the strains in the nine patients to see whether they match those found in area armadillos, said Mara Burger, a spokesperson for the Florida Department of Health.

Every year, between two and 10 people in Florida are diagnosed with leprosy, also known as Hansen's disease, Burger said. This year's cases aren't clustered, and because "the incubation period [the time between exposure and the appearance of symptoms] for Hansen's disease is 2 to 10 years," it can be "difficult to identify the exposure source," Burger told Live Science in an email.

"The disease itself is challenging to diagnose, as many doctors have not come in contact with it before," she said.

Cases of leprosy are also seen in Texas, where between 10 and 25 people were diagnosed each year from 2010 to 2014, said Chris Van Deusen, a spokesperson for the Texas Department of State Health Services. (Texas doesn't have leprosy stats yet for 2015, Van Deusen said.) In Louisiana, health officials recorded eight leprosy diagnoses in 2011 and six a year from 2012 to 2014, said Ashley Lewis, a spokesperson for the Louisiana Department of Health and Hospitals. The state has eight cases reported so far this year, she added.

However, leprosy is relatively difficult to catch. It spreads by prolonged contact with an infected person or animal, and the bacteria are likely dispersed via sneezing or coughing, Schaffner said.

Leprosy primer

The disease, which began infecting humans at least 4,000 years ago, is a chronic condition caused by the bacterium Mycobacterium leprae. It primarily affects the peripheral nerves, skin, upper respiratory tract, eyes and the soft inner lining of the nose, according to the National Institute of Allergy and Infectious Diseases.

People may experience some loss of feeling because the bacteria attack their nerves.

"The nerve can be a little bit swollen," Schaffner said. "If you biopsy the nerve, you can see the leprosy bacteria there."

This lack of sensation, as well as muscle weakness and paralysis, can lead to injuries, and sometimes, people get their fingers, toes and even nose amputated if the disease has progressed too far, Schaffner said.

People can also get leprosy as a blood disease. When that happens, the bacterium slowly infiltrates the tissues under the skin, and causes disfiguring bumps and pouching skin on the face. This can lead to lionlike facial features, in which infected people develop an exaggerated brow and strong cheekbone features, Schaffner said.

"That was part of what made leprosy so offensive or reprehensible to society," Schaffner said. "These people looked fierce and strange."

Many societies ostracized people with leprosy, but successful treatments began in the 1940s, and now the disease is treatable with long-term antibiotic use, Schaffner said. Moreover, approximately 95 percent of people appear to be resistant to infection, Burger added.

An estimated 2 million people around the world are permanently disfigured by leprosy, according to the Centers for Disease Control and Prevention. In the U.S., the National Hansen's Disease Program receives federal money to run 11 clinics in seven states and Puerto Rico that treat the disease, according to the CDC. 

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