Leprosy is a chronic infectious disease caused by the bacterium *Mycobacterium leprae* that primarily affects the skin, peripheral nerves, and mucous membranes of the upper respiratory tract. Its impact on the body is profound and multifaceted, involving a complex interaction between the bacteria and the immune system that leads to nerve damage, loss of sensation, skin lesions, and progressive tissue destruction.
When *M. leprae* enters the body, it targets the skin and peripheral nerves, especially those in cooler areas such as the hands, feet, face, and earlobes. The body’s immune response to the infection determines how the disease manifests. In some cases, the immune system mounts a strong cellular reaction that walls off the bacteria, resulting in a form called tuberculoid leprosy. This form is characterized by firm, dry skin patches with loss of sensation because the nerve fibers in the skin become inflamed and damaged. The immune cells infiltrate all layers of the skin and the underlying tissues, including sweat glands and hair follicles, but the bacteria are few in number due to this effective immune response.
The nerve damage in leprosy is critical because it disrupts the transmission of nerve impulses. This leads to loss of sensation in the affected areas, meaning the person cannot feel pain, heat, or cold. Without this protective sensation, minor injuries go unnoticed and untreated, which can cause wounds to worsen and become infected. Over time, this can result in large ulcers and tissue loss, sometimes severe enough to require amputation. The nerve damage also causes muscle weakness and paralysis, leading to deformities such as clawed hands or foot drop. Facial muscles can be affected too, causing difficulties with blinking and facial expressions, which increases the risk of eye damage and blindness.
In the other form of leprosy, called lepromatous leprosy, the immune response is weaker, allowing the bacteria to multiply extensively. This leads to widespread skin lesions, nodules, and thickening of the skin. The bacteria invade the nerves more diffusely, causing widespread nerve damage and more severe disabilities. The mucous membranes of the nose and throat can also be affected, leading to chronic nasal congestion, nosebleeds, and in advanced cases, collapse of the nasal septum.
Leprosy can also trigger immune reactions known as leprosy reactions, which may occur during or after treatment. These reactions cause painful inflammation, swelling, fever, and further nerve damage, potentially worsening disability. Managing these reactions often requires corticosteroids or other immunosuppressive drugs to reduce inflammation and prevent permanent nerve injury.
Because the nerves are progressively destroyed, the body parts affected by leprosy lose their normal function and appearance. The loss of sensation combined with muscle paralysis leads to deformities and disabilities that can be socially stigmatizing. The damage to the skin and nerves is irreversible if not treated early, but modern multidrug therapy can cure the infection and halt progression.
In summary, leprosy affects the body by infecting and destroying peripheral nerves and skin tissues, leading to loss of sensation, muscle weakness, deformities, and chronic ulcers. The disease’s impact is largely due to nerve damage, which prevents the body from sensing injury and controlling muscles, resulting in progressive tissue destruction and disability.
