Leprosy, also called Hansen's disease, affects 10 –12 million people worldwide. Caused by an unusual bacterium called Mycobacterium leprae, leprosy primarily affects humans. Leprosy is found in tropical areas, such as Africa, South and Southeast Asia, and Central and South America. In the United States, cases of leprosy have been reported in areas of Texas, California, Louisiana, Florida, and Hawaii. Leprosy can take many forms, but the most familiar form is characterized by skin lesions and nerve damage. Although leprosy is curable with various antibiotics, it remains a devastating illness because of its potential to cause deformity, especially in the facial features. Fortunately, antibiotic regimens are available to treat and eventually cure leprosy.

Mycobacterium leprae is an unusual bacterium for several reasons. The bacterium divides...