Current concepts in the pathogenesis of leprosy. Clinical, pathological, immunological and chemotherapeutic aspects.

In recent years there have been notable advances in the laboratory investigation and field management of leprosy. Progress, however, continues to be hindered by the lack of efficient methods for early diagnosis and implementation of control and treatment measures. Diagnosis is still made on the same principles as a century ago (clinical and histopathological findings), and only 1 in 3 known patients worldwide receives optimal chemotherapy. In 1988, nearly 1 in 10 newly diagnosed patients already had debilitating deformities. Contributing factors are operational, administrative and financial difficulties in implementing multidrug therapeutic regimens, inadequately trained personnel, and lack of priority and political commitment to leprosy control. The formulation and implementation of multidrug therapy is the most important development in leprosy in the past 10 years. Dapsone monotherapy was the mainstay for treatment and control for approximately 40 years, but secondary dapsone-resistant strains, first noted in 1964, now infect as many as 50% of all new patients. Multidrug regimens recommended by the WHO consist of various combinations of therapy using dapsone, rifampicin, clofazimine and a thionamide. Duration of therapy is limited to 6 months for paucibacillary and 2 years or more for multibacillary patients; relapse rates thus far are low. The average cost of treatment worldwide, including the cost of drugs, is estimated at $US150 per patient. The recent annual drop of nearly 8% in newly registered patients may be due to the implementation of these therapeutic regimens. Newer drugs that may be introduced into these regimens include fluoroquinolones, minocycline and clarithromycin. While knowledge of the microbiology of the leprosy bacillus and host response has advanced remarkably, there is little improvement in the understanding or amelioration of social aspects of leprosy. Better treatment and control reduces the stigma, but improvements in the attitudes of patients and society towards leprosy are as important as advances in medical science in achieving ultimate eradication of the disease.