Leprosy

Leprosy, also called Hansen's disease (HD), is a long-term bacterial infection.

It is caused by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. This disease is significant because it can cause permanent damage to the skin, eyes, and respiratory tract. Most importantly, it can attack the nervous system.

While the infection is serious, it is not highly contagious. In fact, 95% of people who are exposed to the bacteria do not develop the disease. This is because a person's baseline immune function and genetic factors help prevent the infection from taking hold.

The mechanism of the disease centers on how the bacteria interact with the body. The bacteria are obligate intracellular pathogens, meaning they must live inside host cells to grow. They have been shown to bind to Schwann cells, which are cells that support the nerves. This binding leads to inflammation and nerve injury, such as demyelination. Demyelination is the loss of the protective coating around nerves. This causes a loss of axonal conductance, or the ability of the nerve to send signals. As a result, patients may experience a loss of nociception, which is the ability to feel pain.

Without the ability to feel pain or temperature, people may suffer unnoticed wounds. These injuries can lead to secondary bacterial or viral infections. Over time, this can cause tissue loss, making fingers and toes appear shortened or deformed.

Doctors classify leprosy into two main types based on the bacterial load. The first type is paucibacillary leprosy. A person with this type has five or fewer skin patches that are poorly pigmented and numb. The second type is multibacillary leprosy. These patients have more than five skin patches and a higher number of bacteria in their bodies. Diagnosis is confirmed through a skin biopsy. During this process, doctors look for acid-fast bacilli, which are bacteria that retain certain red stains under a microscope.

The history of leprosy is very long and spans thousands of years. The name comes from a Greek word meaning "scale." The term Hansen's disease honors the Norwegian physician Gerhard Armauer Hansen.

The study of this disease is known as leprology. Historically, the disease has been linked to social stigma. This stigma often prevented people from seeking early treatment. In some places, people were forced into leper colonies to live apart from society.

While Japan repealed its Leprosy Prevention Laws in 1996, some former patients still live in sanatoriums. In the past, some people even used leper bells to warn others of their presence.

Global numbers show that leprosy is becoming much less common. In the 1980s, there were 5.2 million cases worldwide. By 2020, that number fell to fewer than 200,000 cases.

Most new cases are concentrated in just 14 countries. India is responsible for more than half of all new cases globally. Despite these challenges, the progress is huge. Between 1994 and 2014, 16 million people were cured of the disease.

Today, leprosy is a curable condition using multidrug therapy (MDT).

This treatment uses specific antibiotics to kill the bacteria. For paucibacillary leprosy, patients take dapsone, rifampicin, and clofazimine for six months. For multibacillary leprosy, the same medicines are used for 12 months. The World Health Organization provides these treatments free of charge. Once a person starts this therapy, they are considered non-infectious after 72 hours. This allows patients to live normally with their families, attend school, and go to work.

Leprosy is also a zoonotic disease, meaning it can spread between animals and humans. Research shows that armadillos can carry the bacteria. It is suspected that armadillos acquired the bacteria from European explorers.

In 2016, researchers also found the bacteria in red squirrels in Great Britain. This connection to animals shows how complex the spread of the disease can be. Understanding these links helps scientists better manage the disease in both humans and nature.