Leprosy, also known as Hansen’s disease, is a chronic infectious condition that has affected humanity for thousands of years. This curable disease is primarily caused by the bacterium Mycobacterium leprae, which slowly damages the peripheral nerves and targets various parts of the body, including the skin, eyes, and upper respiratory tract. While historically associated with severe stigma, modern medicine offers effective treatments that can fully cure individuals and prevent long-term complications.
Characteristics of Mycobacterium leprae
Mycobacterium leprae was first identified in 1873 by Gerhard Armauer Hansen, marking the first time a bacterium was confirmed as the cause of a human disease. This microorganism is a rod-shaped, acid-fast bacillus, meaning it retains certain dyes even after being washed with an acid-alcohol solution. It functions as an obligate intracellular parasite, requiring host cells for its survival and replication.
A notable feature of Mycobacterium leprae is its exceptionally slow growth rate, with a doubling time of approximately 12 to 14 days. The bacterium thrives in cooler body temperatures, explaining its predilection for sites such as the skin, peripheral nerves, upper respiratory tract, eyes, and testes. Unlike most bacteria, Mycobacterium leprae cannot be grown in artificial laboratory media; instead, scientists rely on animal models like the nine-banded armadillo and the footpads of mice for studies.
How the Bacteria Is Transmitted
Transmission of Mycobacterium leprae occurs primarily through respiratory droplets expelled from the nose and mouth of an untreated, infected individual. Despite historical misconceptions, leprosy is not highly contagious and requires prolonged, close, and frequent contact for transmission. Casual interactions, such as shaking hands or hugging, do not typically lead to the spread of the disease.
The vast majority of the global population, estimated at about 95%, possesses a natural immunity to the bacterium, further limiting its transmission. Once an infected individual begins appropriate antibiotic treatment, they rapidly become non-infectious, usually within a few days, stopping the chain of transmission. Symptoms can take anywhere from nine months to over 20 years to appear, though the average incubation period is approximately five years.
Symptoms and Diagnosis
Leprosy primarily manifests through its effects on the skin and peripheral nerves, which are the nerves outside the brain and spinal cord. Early signs include discolored skin patches with a definitive loss of sensation, meaning the affected area cannot feel touch, heat, or pain. The disease can also present as lumps, bumps, or generalized thickening of the skin.
Damage to the peripheral nerves can lead to muscle weakness, paralysis in the hands and feet, and potential disfigurement if untreated. This nerve damage also results in a loss of sensation, leaving affected extremities vulnerable to unnoticed injuries. Leprosy is classified into two main forms based on the body’s immune response: tuberculoid leprosy, with fewer skin lesions and limited bacteria, and lepromatous leprosy, with widespread lesions and a higher bacterial load.
Diagnosis is made through a clinical examination, looking for these cardinal signs. Confirmation involves taking a skin or nerve biopsy, where tissue samples are examined under a microscope for acid-fast bacilli. A slit-skin smear is also a diagnostic method to identify the bacteria.
Treatment and Elimination of the Bacteria
Leprosy is a curable disease, and the standard medical approach involves Multi-Drug Therapy (MDT), a treatment regimen recommended by the World Health Organization (WHO). This therapy combines several antibiotics to eliminate the bacterium from the body. The primary medications used in MDT are rifampicin, dapsone, and clofazimine. Using multiple drugs simultaneously prevents the development of antibiotic resistance.
The duration of treatment varies by disease classification: individuals with paucibacillary leprosy receive treatment for six months, while those with multibacillary leprosy are treated for 12 months. MDT is highly effective, with a cure rate over 98% and a very low relapse rate. The WHO has played a significant role in global leprosy control by providing MDT free of charge in many countries, reducing the disease’s prevalence worldwide and stopping its transmission.