by Whit Gibbons

June 26, 2005

Armadillos are literally on the move. I have recently seen reports of their becoming established in northern Missouri, Iowa, and Illinois. About ten years ago was the first time I had seen a live armadillo in central South Carolina. Maps in the most recent Peterson field guide for mammals show them nowhere near these states. Aside from their bizarre appearance and a talent for dispersal, some armadillos in Louisiana have another unusual trait. They have leprosy.

Armadillos are the only animal besides humans in which populations harbor leprosy. Leprosy, or Hansen's disease, is caused by a type of bacteria closely related to the one that causes tuberculosis. But medical researchers have yet to find a satisfactory way to culture the leprosy bacteria in the laboratory for study. Armadillos are kept in captivity at medical facilities so researchers have the bacteria on hand to test treatments and study the microorganism.

But a big mystery remains. How is leprosy transmitted? Pieces of the puzzle have been investigated by Kim Marie Tolson, a wildlife biologist at Northeast Louisiana University. As part of her research program, she and her students capture armadillos and assess them for the presence of leprosy. Leprosy has been recognized as a human affliction since biblical times, although Tolson thinks many of the references to it in the Bible were actually other skin diseases. Nonetheless, the disease still exists. Studying afflicted armadillos might provide insights into how the disease is transmitted and other aspects of its biology.

Armadillos often live more than ten years, which is important. The incubation period for the bacteria is at least two years, and possibly five or six, before it is expressed. Being long-lived is a requirement for acquiring leprosy. For example, even if possums were susceptible, their normal life span is only about two years; therefore, they would not have time to get leprosy.

Tolson's research involves catching armadillos as they scurry aboveground at her field sites in northern Louisiana. When she goes "dillering," as armadillo collecting is called, she takes several volunteers, each armed with a long-handled net. Armadillos have extraordinarily poor eyesight, making some of the chases as humorous as they are exciting. Tolson speaks of one armadillo that escaped because it ran smack into an oak tree and then turned and ran between the legs of a pursuer. Apparently, armadillos are hard to catch when you are laughing.

The captured animals, which may number as many as 60 in one day, are carried to the university where skin samples are taken and the animals are given identification marks. Samples are taken from the ears and lymph nodes, common locations of leprosy infections. The marking is done with a tattoo press, each animal receiving its personal ID on the inside of the shell-like outer covering. Animals are released at their site of capture within 72 hours, with the researchers hoping to recapture them later.

One-fourth of the armadillos captured in Tolson's study have identifiable leprosy. Others may have been exposed but are carriers only or have not yet manifested the symptoms. Humans generally show signs of leprosy through deterioration of the extremities. Armadillos seem to have a bigger problem: the disease is usually fatal. Tolson has even discovered leprosy infections in the bone marrow. These funny-looking mammals are indeed completely susceptible to the disease throughout their systems. However, most of them lose their lives on highways, as armadillos, like possums, are seriously road-challenged.

One point Tolson makes about the ecology of leprosy in armadillos is that most of the infected animals come from bottomland hardwood forests rather than from more open, drier habitats. Also, virtually all reported cases of leprosy in armadillos have been west of the Mississippi River, hence not in Florida where the largest eastern populations occur, and as far as is known, not in the many new areas armadillos are moving into. Incidentally, few if any humans have ever been known to contract leprosy from the Louisiana armadillos.

Although Hansen's disease does not have the social stigma associated with it in earlier times and can usually be controlled with medication in humans, it's nice to know we have the armadillo as a partner for studying it.

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