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Infectious Disease and Microbiology - Leprosy
Leprosy is a chronic infectious disease caused by Mycobacterium leprae, an acid-fast, slow-growing intracellular organism that primarily affects the skin and peripheral nerves. The disease has a long incubation period, typically ranging from 5 to 7 years, and is transmitted mainly through prolonged close contact, likely via respiratory droplets or direct contact with untreated skin lesions. The organism has a predilection for cooler areas of the body, particularly the skin and peripheral nerves, where it infects Schwann cells and leads to nerve damage.
Leprosy remains a global health concern, although its prevalence has significantly declined over recent decades due to effective multidrug therapy. It is most common in endemic regions such as Brazil, India, Indonesia, and parts of Africa and Southeast Asia. Risk factors include close household contact with infected individuals, extremes of age (children and older adults), and impaired cell-mediated immunity. Genetic susceptibility also plays a role, influencing disease type and severity.
The clinical presentation varies widely depending on the host immune response. Patients typically present with hypopigmented or erythematous skin lesions accompanied by sensory loss, which is a hallmark feature. In tuberculoid disease, lesions are few, well-defined, and associated with localized nerve involvement. In contrast, lepromatous disease is characterized by numerous lesions, nodules, and diffuse skin involvement, often with more extensive nerve damage. Advanced cases may lead to deformities such as loss of eyebrows, hoarseness, and the classic saddle-nose deformity due to cartilage destruction.
Diagnosis is primarily clinical, based on the presence of characteristic skin lesions with sensory loss and thickened peripheral nerves. Skin smears or biopsies may be used to confirm the diagnosis, showing either granulomatous inflammation with few organisms in tuberculoid disease or numerous bacilli in lepromatous disease. The disease is also classified by the World Health Organization into paucibacillary and multibacillary forms based on lesion number and bacterial load.
Treatment involves prolonged multidrug therapy to prevent resistance and ensure cure. Multibacillary disease is treated with a combination of dapsone, rifampin, and clofazimine for an extended duration, while paucibacillary disease requires a shorter regimen with fewer drugs. Alternative agents such as fluoroquinolones, macrolides, and tetracyclines may be used in certain cases. Close monitoring is essential during therapy due to potential drug side effects and immune-mediated reactions.
The prognosis is excellent with appropriate treatment, but complications can arise, particularly involving the immune system. Type I (reversal) reactions involve worsening inflammation and nerve damage, while Type II reactions, known as erythema nodosum leprosum, present with systemic symptoms such as fever and painful nodules. Long-term complications include permanent nerve damage, disability, and deformities if untreated. Early diagnosis and adherence to therapy are crucial in preventing these outcomes.
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