Leprosy, also known as Hansen’s disease, is caused by M. leprae, and has been known since antiquity. Although this organism was first described by Hansen in 1873 (9 years before Koch’s discovery of the tubercle bacillus), efforts to grow the organism in vitro on agar and other bacteriologic media have remained unsuccessful. Leprosy occurs in one of two clinical presentations: lepromatous (multibacillary) leprosy or tuberculoid (paucibacillary) leprosy. Since the 1940s when dapsone was recognized as an effective antimicrobial therapy, the global disease burden has been significantly reduced, due to the successful use of antimicrobial therapy and the start of the WHO’s campaign efforts to eliminate leprosy in 1991. According to the WHO database, 136 countries reported new cases of leprosy in 2015. Globally, the majority of cases occur in India (60%), Brazil (13%), and Indonesia (9%). In the United States, leprosy is a rare disease; in 2015, 178 new cases were reported, with most of these cases being reported in the following States: Arkansas, California, Florida, Hawaii, Louisiana, New York, and Texas. The epidemiology of leprosy in the United States closely reflects immigration patterns, and the majority of patients (approx. 60%) were born outside the United States. Detailed data are available from the CDC, the U.S. National Hansen’s Disease Program, and the WHO.

Typical acid-fast bacilli—singly, in parallel bundles, or in globular masses—are regularly found in scrapings from skin or mucous membranes (particularly the nasal septum) in patients with lepromatous leprosy. The bacilli are often found within the endothelial cells of blood vessels or in mononuclear cells. When bacilli from human leprosy (ground tissue nasal scrapings) are inoculated into the footpads of mice, local granulomatous lesions develop with limited multiplication of bacilli. Inoculated armadillos develop extensive lepromatous leprosy, and armadillos naturally infected with leprosy have been found in Texas and Mexico. M. leprae from armadillo or human tissue contains a unique o-diphenoloxidase, perhaps an enzyme characteristic of leprosy bacilli.

Clinical Findings

 The onset of leprosy is insidious. The lesions involve the cooler tissue of the body, including the skin, superficial nerves, nose, pharynx, larynx, eyes, and testicles. The skin lesions may occur as pale, anesthetic macular lesions 1–10 cm in diameter; diffuse or discrete erythematous, infiltrated nodules 1–5 cm in diameter; or a diffuse skin infiltration. Neurologic disturbances are manifested by nerve infiltration and thickening, with resultant anesthesia, neuritis, paresthesia, trophic ulcers, and bone resorption and shortening of the digits. The disfigurement caused by the skin infiltration and nerve involvement in untreated cases may be extreme.

The disease is divided into two major types: lepromatous and tuberculoid, with several intermediate stages (see the Ridley-Jopling classification system). In the lepromatous type, the course is progressive and malignant, with nodular skin lesions; slow, symmetric nerve involvement; abundant acid-fast bacilli in the skin lesions; continuous bacteremia; and a negative lepromin (extract of lepromatous tissue) skin test result. In lepromatous leprosy, cell-mediated immunity is markedly deficient, and the skin is infiltrated with suppressor T cells. In the tuberculoid type, the course is benign and nonprogressive, with a small number of macular skin lesions containing few bacilli, severe asymmetric nerve involvement of sudden onset, and a positive lepromin skin test result. In tuberculoid leprosy, cell-mediated immunity is intact, and the skin is infiltrated with helper T cells.

Systemic manifestations of anemia and lymphadenopathy may also occur. Eye involvement is common. Amyloidosis may develop.

Diagnosis

 Scrapings with a scalpel blade from skin or nasal mucosa or from a biopsy of earlobe skin are smeared on a slide and stained by the Ziehl-Neelsen technique. Biopsy of skin or of a thickened nerve gives a typical histologic picture. No serologic tests are of value. Nontreponemal serologic tests for syphilis frequently yield false-positive results in patients with leprosy.

Treatment

Sulfones such as dapsone (see Chapter 28) are first-line therapy for both tuberculoid and lepromatous leprosy. RMP and/ or clofazimine generally are included in the initial treatment regimens. Other drugs active against M. leprae include minocycline, clarithromycin, and some fluoroquinolones. Regimens recommended by the WHO are practical. Several years of therapy may be necessary to adequately treat leprosy. Epidemiology While it is currently not exactly known how M. leprae spreads among people, transmission of leprosy is most likely to occur via respiratory droplets (eg, cough and sneezing) from an infected individual to a healthy person. Prolonged and close contact with infected individuals is necessary for effective transmission of the organism; nasal secretions are the most likely infectious material for family contacts. Casual contact (eg, shaking hands) with a person who has leprosy does not pose a risk for transmission of the organism. The incubation period for leprosy is probably 2–10 years. Without prophy laxis, about 10% of exposed children may acquire the dis ease. Treatment tends to reduce and abolish the infectivity of patients. In the southern United States (eg, Texas) and Mexico, some armadillos are found to be naturally infected with M. leprae. Recent studies suggest that armadillos may be a source of human infection in the southern United States; however, the risk of transmission to human appears to be low, specifically when appropriate precautions are used when handling potentially infected animals.

 Prevention and Control

In the United States, the current recommendations for prevention of leprosy include a thorough examination of household contacts and close relatives. This should include a complete skin examination and an examination of the peripheral nervous system. The U.S. Public Health Service National Hansen’s Disease Program does not recommend routine dapsone prophylaxis. A therapeutic trial may be indicated for patients whose signs and symptoms are suggestive of leprosy but who do not have a definitive diagnosis.

 BCG does provide some protection against leprosy especially among household contacts of cases.

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