Armadillos likely source of human leprosy

Published on July 01, 2011
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Armadillos appear to be a likely cause of human cases of leprosy in the southern United States, according to an article published in late April.

A scientific report in the New England Journal of Medicine, which was available online April 28, indicates about 150 new cases of leprosy, or Hansen's disease, are reported in the U.S. annually and that about a third of these cases involved patients who lived solely in the U.S., did not recall contact with another infected person, and appeared to have acquired the disease from a local source. The researchers isolated nearly identical strains of Mycobacterium leprae from 28 of 33 wild armadillos and from 25 of the 39 patients who lived in areas of the U.S. where they could be exposed to armadillos. They found different strains in people who were infected in the Philippines and Brazil.

Richard W. Truman, PhD, a research scientist for Hansen's disease programs in the Health Resources and Services Administration, said the data confirm a long-held hypothesis that armadillos can be a source of infection in humans and that leprosy is probably a zoonosis in the southern United States. He noted that the bacteria that cause leprosy are found only in humans and in nine-banded armadillos, or Dasypus novemcinctus. Other types of armadillos, including six-banded armadillos that have been kept as pets, are not known to carry the bacteria. 

Research findings published in the New England Journal of
Medicine indicate nine-banded armadillos, or Dasypus novemcinctus,
that are found in the U.S. can spread leprosy to humans.

Dr. Truman hopes that the study will help people take appropriate measures to decrease their risk of infection from exposure to armadillos, although he noted that the risk is already low. HRSA information also indicates that 95 percent of people are immune to infection with M leprae.

"If we can discourage people from having frequent direct contact with armadillos, that's probably beneficial," Dr. Truman said. "But there's no real reason to panic about this infection or to take drastic steps to eliminate armadillos from their environments."

Dr. Truman noted that efforts to eliminate armadillos, such as shooting the animals, could raise people's risk of infection.

James L. Krahenbuhl, PhD, director of Hansen's disease programs for HRSA, said the study could also aid physicians in identifying and treating the rare disease.

"Our goal in dealing in the aftermath of this terrific research report is basically to educate physicians that they may see leprosy and that we have a program here and we can help them," Dr. Krahenbuhl said. He noted that the federal program works with about 550 private practice physicians who have at least one patient with Hansen's disease.

The study's 11 authors worked on the project for at least 18 months in the U.S., France, Switzerland, and Venezuela, Dr. Truman said. Although previous studies had indicated exposure to armadillos could be a risk factor, he said such studies also found that general exposure to wildlife could be an equivalent risk factor. Previous studies of risk factors for the disease had faced difficulties because of the 3- to 5-year gap between infection and the onset of clinical symptoms, as well as the frequency of misdiagnosis, he said.

The disease is known to be present in armadillos at high rates only in lowland areas of Alabama, Arkansas, Louisiana, Mississippi, and Texas, Dr. Truman said.

More information from the New England Journal of Medicine is available at