Leprosy in the US: Are armadillos playing a role? Experts explain.

There's a medical mystery brewing in Florida and an unsuspecting, mild-mannered mammal may be at the center of it.

Some experts say the nine-banded armadillo may be behind a rise in domestically transmitted cases of leprosy. Another group quick to defend the armored creature says there's little data to support armadillos – which are known to carry the bacteria that causes leprosy – are directly causing the uptick.

Dr. Jessica Fairley, who teaches medicine and global health at Emory University School of Medicine, suspects the human-armadillo contact may be a contributing factor.

"This uptick in Florida is telling us this isn't like some outbreak," said Fairley, director of the Hansen's Disease Program at Emory University Hospital Midtown. "We need to be looking at our environmental health and how we interact with the environment."

Brett DeGregorio, a wildlife biologist with the United States Geological Survey Michigan Cooperative Research Unit at Michigan State University, isn't buying that theory. Armadillos are "going to get scapegoated for this leprosy (outbreak) but I don't think they're playing much of a role," he said.

The decadeslong debate resurfaces every time health officials report a new case of leprosy, also called Hansen's disease, yet scientists have made little progress in pinpointing how the disease is transmitted.

In the meantime, armadillos have continued to expand their territory northward partly due to climate change, possibly bringing leprosy with them. As experts note domestic cases are becoming more common, scientists are eager to know whether the prehistoric-looking creatures are the culprit.  

Armadillo controversy

While the majority of leprosy cases are transmitted to the U.S. through international travel, a Centers for Disease Control and Prevention report in August suggests the disease is becoming endemic to the southeastern parts of the country, where armadillos are often found.  

Nine-banded armadillos are the only mammals other than humans that have been shown to carry Mycobacterium leprae, or M. leprae, the bacteria that causes leprosy.

In Brazil, where armadillos are considered a delicacy, doctors have linked cases of leprosy to people eating the animal and hypothesized that they could have transmitted the disease to family members living in close quarters, said John Spencer, an associate professor in the department of microbiology, immunology and pathology at Colorado State University.

But it's hard to trace infections. Not everyone who comes in contact with an infected armadillo or person will develop leprosy because more than 95% of people are naturally immune to the disease, said Spencer, who has researched leprosy in Brazil for the past 20 years.

Leprosy in America:It could become endemic to Florida. Here is what to know.

This makes leprosy particularly hard to study. There's not much data on animal-to-human transmission in the U.S., but research shows that a relatively large percentage of armadillos in southern states have the bacteria.

A 2015 study from researchers at the National Hansen's Disease Program found more than 16% of nearly 650 armadillos tested in Mississippi, Alabama, Georgia and Florida harbored the bacteria.

They also looked at samples that were taken and stored frozen from 1988 to 1993 and others from 2009 but didn't find the bacteria, which could suggest the number of infected armadillos may be growing.

Still, more armadillos carrying leprosy doesn't mean armadillos are directly causing leprosy, wildlife experts say.

The most recent case of leprosy reported in Florida came from a 54-year-old man who hadn't traveled and had no known exposure to armadillos, according to the CDC. It's unclear how he was infected, but health officials say he spent long periods of time outdoors as a landscaper and had prolonged contact with people from leprosy-endemic countries.

However, the early symptoms of the disease include loss of feeling in your hands or feet; dry, stiff, or painful areas of the skin; and the loss of hair from the eyebrows or eyelashes. Doctors prescribe antibiotics to patients with leprosy. Patients are typically no longer infectious after a few days of antibiotics, but the treatment lasts between one to two years due to the bacteria's slow growth.

Why did the armadillo cross the road? Climate change

Although the armadillo debate is far from settled, the armored mammal has continued to expand its territory.

The primarily nocturnal animal originated in South America and migrated to the U.S. crossing through Central America, Mexico and the Rio Grande River in the 1850s. It then expanded to states such as Texas, Louisiana, Mississippi, Alabama and Georgia.

Their arrival in Florida was accidental, experts say, after armadillos escaped a small zoo and circus in the 1920s and 30s.

They've been expanding northward ever since, with recent sightings reported as north as southern Indiana, Tennessee and Illinois, DeGregorio said.

Rising temperatures due to climate change are creating more habitable environments for armadillos in areas with historically colder climates, he said. Human development has also aided their trek northward as they tend to travel along the forests that line main roads. There's been some evidence that they can even hitchhike on trucks.

"We've made a very easy travel corridor for them – low medians and the forest(ed), grassy areas around roads," DeGregorio said. "That makes an easy walking path for an armadillo to follow."

Some experts argue their expanding territory and ability to survive new areas could increase the proportion of domestically contracted cases of leprosy. Others are more skeptical.

"When people hear about armadillos expanding, they think it's going to increase the risk of leprosy to the human population and at this point, there isn't much evidence of that," said Jim Loughry, a retired biology professor from Valdosta State University.  

Much to the dismay of wildlife experts, armadillos will likely remain the prime suspects in this unsolved mystery until more research is done.

Follow Adrianna Rodriguez on X, formerly Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

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