In Canada and the U.S., leprosy is now a relatively uncommon disease, with only several thousand diagnosed cases, usually treated with drugs on an outpatient basis. In developing countries, however, leprosy is a serious health problem. The World Health Organization has reported an estimated 10 to 12 million cases of leprosy world-wide, with more than half of them untreated.

 

In its worst form, leprosy can cripple and disfigure. The search for a vaccine has become more urgent because the drugs used to treat leprosy are showing signs of losing their effectiveness as the disease becomes more immune to them.

 

Leprosy is a bacterial disease whose roots can be traced back to the beginning of history. To produce a vaccine, the leprosy bacillus must first be grown under laboratory conditions for study. While the bacillus was actually isolated more than a century ago, it was not until the early 1970's that researchers discovered the armadillo as a model for leprosy.

 

The nine-banded armadillo is one of the few creatures other than humans that can be infected with the leprosy bacillus. Its body temperature is 90 degrees, 8.6 degrees lower than the temperature of most mammals, including humans. In people, the leprosy bacillus concentrates in the body's cool extremities, such as the fingers and ears, while in the armadillo, all of its lukewarm organs turn out to be ideal incubators for the bacillus.

 

The armadillo's susceptibility to leprosy was discovered in the laboratory in the late 1960's, and later researchers found that many wild armadillos in the southeastern U.S. already had the disease. After decades of effort, it is still impossible to grow the leprosy bacillus in culture, so armadillos are the major source of the bacilli for study.

 

By studying transmission of leprosy in these natural armadillo populations, medical researchers will eventually learn how this ancient disease spreads in humans. Meanwhile, armadillos are supplying bacilli used in leprosy vaccines which are now being tested on more than a half million people in developing countries where the disease is prevalent.