Hansen’s disease, the preferred name for leprosy, is a chronic bacterial infection that is now highly treatable and curable. Death directly caused by the bacteria is rare. The primary danger comes from the progressive, permanent damage it causes to the nervous system, which, if left untreated, can lead to severe secondary complications that ultimately prove fatal.
The Cause and Modern Context of Hansen’s Disease
Hansen’s disease is caused by the slow-growing bacterium Mycobacterium leprae. This bacterium is an obligate intracellular parasite, meaning it must live inside host cells. It has an unusually long incubation period, with symptoms often taking between 2 and 10 years to appear after initial infection, though some cases may take 20 years or more.
Transmission is thought to occur through respiratory droplets from an untreated infected person. However, the disease is not highly contagious, and approximately 95% of the global population is naturally resistant. While rare in developed countries, it remains a public health concern in parts of Africa, Asia, and the Americas.
How Leprosy Damages the Body
The primary mechanism of disease progression involves the bacteria’s predilection for the peripheral nervous system and cooler areas of the body, such as the extremities, eyes, and nasal passages. M. leprae specifically invades Schwann cells, which insulate and support peripheral nerve fibers. This invasion, combined with the body’s inflammatory immune response, leads to the progressive destruction and demyelination of the nerves.
Damage to the sensory nerves results in a loss of sensation (anesthesia) in the affected areas. This inability to feel pain, heat, or cold is the root cause of many physical manifestations. Damage to the motor nerves causes muscle weakness and atrophy, leading to conditions like “clawed hand” or “dropped foot” due to paralysis. Autonomic nerve damage can also occur, affecting functions like sweating and tear production, which leaves the skin dry and the eyes vulnerable to injury.
Secondary Complications That Lead to Mortality
Mortality is caused by secondary, preventable complications that arise from irreversible nerve damage, not the Mycobacterium leprae infection itself. The most common pathway to death is through chronic infection and subsequent systemic sepsis. Because the hands and feet have lost sensation, repeated, unnoticed injuries such as cuts, burns, or pressure ulcers occur frequently.
These chronic, open wounds provide a constant entry point for other bacteria, leading to deep tissue infections that the patient often does not feel until they are severe. If local infections are not properly managed, the bacteria can spread into the bloodstream, resulting in sepsis—a life-threatening immune response that frequently causes organ failure and death. Another severe complication is the occurrence of intense inflammatory episodes known as Lepra Reactions, which can happen during or after antibiotic treatment.
These reactions result from the body’s heightened immune response and involve severe inflammation of the nerves and sometimes internal organs. In advanced, chronic cases, this persistent inflammation can lead to amyloidosis, where abnormal protein deposits accumulate in organs, most notably the kidneys. Amyloidosis can progress to severe renal insufficiency or complete kidney failure, which is a common terminal event in long-standing, untreated multibacillary leprosy.
Curative Treatment and Prevention
The modern standard of care, Multi-Drug Therapy (MDT), has transformed Hansen’s disease into a curable condition. MDT uses a combination of antibiotics—typically rifampicin, dapsone, and clofazimine—administered over a fixed period (usually 6 to 12 months). This combination therapy is highly effective, killing the M. leprae bacteria, halting disease progression, and preventing drug resistance.
MDT eliminates the bacteria, removing the primary source of the inflammatory and neurodestructive process. By stopping the disease’s progression, MDT effectively prevents the further nerve damage that serves as the precursor to fatal secondary complications like sepsis and organ failure. Early diagnosis and the immediate initiation of MDT are paramount, ensuring the greatest chance of preventing further nerve damage, disability, and subsequent mortality.