A surprise lesson arrived in my snail mailbox today: the April 28 issue of NEJM includes a fascinating research paper on a probable cause of leprosy in the southern U.S. New, detailed genetic studies show that armadillos, long-known to harbor the disease, carry the same strain as occurs in some patients; they’re a likely culprit in some cases.

Dr. Gerhard Henrik Armauer Hansen, who identified the bacteria causing leprosy

Dr. Gerhard Henrik Armauer Hansen, who identified the bacteria causing leprosy

For those who didn’t go to med school: Leprosy is a chronic, infectious disease cause by Mycobacterium leprae. In my second year we were told to refer to the illness as Hansen’s disease. We learned that some people are more susceptible to it than others, possibly due to inherited immunological differences, a point that is reiterated in the current article.

The World Health Organization reports there are under 250,000 cases worldwide every year. Here in the U.S., Hansen’s disease is quite rare, with about 150 new cases reported annually according to the study authors. The condition wasn’t evident in the Americas before Columbus’ travels, but by the mid-18th Century it was affecting some settlers near New Orleans. Today, most cases in the U.S. arise in travelers and others who’ve lived or worked abroad in regions where leprosy is endemic. About a third crop up in people who’ve never left the country, and these cases tend to cluster in the southeastern U.S.

Leprosy tends to affect the skin, and what the NEJM investigators first did was examine skin biopsy specimens from patients who live in the U.S. and hadn’t traveled. It’s been known for decades that armadillos can carry these bacteria, and so the researchers took specimens from wild armadillos in five southern states, and analyzed the M. leprae bacterial genomes. They matched. Then they looked at more patients’ samples, and also analyzed M. leprae sequences from patients in other parts of the world.

The conclusion is that wild armadillos and some leprosy patients in the southern U.S. are infected with an identical strain of the bacteria that causes leprosy. From this information, the authors infer that armadillos are a reservoir for this stigmatizing germ, and that they may be the source of some patients’ infections.

So the news is that leprosy may be a zoonosis.

A personal note –

Only once I saw a patient with Hansen’s disease, at the Bellevue dermatology clinic, when I was a fourth-year student. She was an elderly woman from China. Her face, which I can picture now, had classic leonine features. The resident caring for her,  an intern with a plan to become a dermatologist, prescribed antibiotics.

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