Every year, about 200 new cases of leprosy are diagnosed in the United States. Most patients come from countries such as India and Brazil, where leprosy is still common. Rarely, leprosy occurs out of the blue, as in the handful of cases in the past two decades in New Yorkers without clear risk factors, who were perhaps exposed to undiagnosed immigrants with the disease. A full one-third of leprosy cases in America occur in Southerners who have never travelled outside the US. Florida has been a leprosy hotspot in recent years, with 27 cases in 2015 and 18 cases in 2016.
What in the sweet Sam Hill is going on with leprosy in old Dixie? Mycobacterium leprae, the bacteria responsible for leprosy, is still something of an enigma. For unclear reasons, most people are innately resistant to infection with it. However, it thrives in those who are vulnerable, multiplying to astronomical numbers in the skin and along the nerves, leading to skin deformities and nerve damage. (It does not invade deeper organs, as it cannot tolerate warmer temperatures.) Strangely, it has proven impossible to grow on culture media in the lab. Besides human beings, only two other animals seem to become infected: the nine-banded armadillo of the southern United States, and the European red squirrel (like impertinent Squirrel Nutkin from Beatrix Potter). The armadillo is especially prone to becoming leprous, perhaps because of its low body temperature, and may play a key role in leprosy transmission south of the Mason-Dixon line. Up to 20% of armadillos are infected with leprosy, and the leprosy strain found in armadillos is identical to that seen in southerners with leprosy. Human leprosy cases in Florida have been associated with getting splattered with armadillo roadkill, hunting and skinning armadillos, and gardening in soil full of armadillo droppings. Some will be happy to know that well-cooked armadillo meat does not seem to transmit leprosy. Leprosy also seems to grow and survive in soil, which could be a source of infection in those without a history of exposure to lepers, armadillos, or leper armadillos.
Leprosy may pose a risk to tourists as well, including the Canadian snowbirds who schlep down south every winter to escape white snow and black ice. A retired Nova Scotian farmer was recently diagnosed with lepromatous leprosy, apparently acquired from wintering in the central Florida region where leprosy transmission is most common. Although he had no known armadillo exposure, the leprosy strain found in his skin matched that seen in armadillos. The authors concluded that “travelers to the southern United States would be wise to avoid contact with armadillos.”
The nine-banded armadillo is a recent arrival in the United States from South America, having been first found in the Rio Grande valley of Texas in the 1840s. Since then, it has spread widely across the South. It does well in human environments, burrowing under porches and eating grubs and ants found in disturbed soils and suburban lawns. In recent years, perhaps aided by development, climate change, and their robust front crawl, armadillos have been making their way north into Virginia and Illinois, and as far west as Nebraska. Will zoonotic leprosy come with them?