A chronic bacterial disease caused by Mycobacterium leprae, endemic in many areas of Asia, Africa, the Pacific Islands, Latin America and the southern U.S., involving mainly skin, peripheral nerves, and the mucosa of the upper airway. The following characteristics are typical of the major forms of the disease:

• Tuberculoid: one or a few well-demarcated, hypopigmented, and anesthetic skin lesions, frequently with active, spreading edges and a clearing center; peripheral nerve swelling or thickening also may occur;
  
• Lepromatous: a number of erythematous papules and nodules or an infiltration of the face, hands, and feet with lesions in a bilateral and symmetrical distribution that progress to thickening of the skin;
  
• Borderline (dimorphous): skin lesions characteristic of both the tuberculoid and lepromatous forms;
  
• Indeterminate: early lesions, usually hypopigmented macules, without developed tuberculoid or lepromatous features.

Humans are the only reservoir of Mycobacterium leprae of proven significance. Although the exact mode of transmission is not clearly established, household and prolonged close contact appear to be important. The incubation period is from 9 months to 20 years, the average is probably 4 years for tuberculoid leprosy and twice that for lepromatous leprosy.

CASE CLASSIFICATION

1. CONFIRMED
   
   A clinically compatible case AND
   
   • Demonstration of acid-fast bacilli in skin or dermal nerve, obtained from a full-thickness skin biopsy of a lepromatous lesion.
     
     
2. PROBABLE
   
   Not used
   
   
3. POSSIBLE
   
   Not used

What you should know about Hansen's Disease (Leprosy), (Mycobacterium leprae)?