Leprosy Risk Factors

People at highest risk are those who live in the areas where leprosy is endemic (parts of India, China, Japan, Nepal, Egypt, and other areas) and especially those people in constant physical contact with infected people. In addition, there is some evidence that genetic defects in the immune system may cause certain people to be more likely to become infected (region q25 on chromosome 6).

What is leprosy?

Leprosy also termed Hansen’s disease, is a chronic infection caused by the bacterium Mycobacterium leprae, a rod-shaped organism that stains reddish when an acid-fast stain is applied. Historians suggest leprosy was recognized as a disease as early as 600 BC; because of the disfigurement of individuals with untreated leprosy, people with leprosy have been shunned and isolated for many centuries. Fortunately, current multidrug therapy (MDT) has reduced leprosy so effectively that only a few countries still have individuals with this disease. Currently, the disease is rarely seen in the United States.

Leprosy has been classified into two major types: tuberculoid and lepromatous. However, there are intermediate subtypes (borderline, mid-borderline, and others). Tuberculoid leprosy has a more limited disease pattern and relatively few bacteria located in the infected tissue, while patients with lepromatous leprosy have the widespread disease and much larger numbers of bacteria in infected tissue. These terms are still seen in the literature but are being replaced by the terms paucibacillary (for tuberculoid) and multibacillary (for lepromatous) types.

Mycobacterium leprae can infect armadillos that are indigenous to the southwest United States; occasionally, people can get leprosy if they handle these animals. Another form of leprosy is seen in dogs and cats (canine leprosy). Although canine leprosy is caused by Mycobacterium species, there is no good evidence that canine leprosy is transmitted to humans by pets.