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Leprosy is a chronic and progressive disease that primarily affects the skin and peripheral nervous system. The disease has been with us for thousands of years. There is evidence of the disease as far back as 4000 BC, in ancient Egypt.  In 1873, Norwegian physician Dr. Gerhard Armauer Hansen discovered that leprosy was caused by a bacterium.  Today, we call this bacterium Mycobacterium leprae, and we often refer to leprosy as Hansen’s Disease, in honor of Dr. Hansen. While leprosy caused significant morbidity and mortality in the past, cases today are rare and are curable with proper treatment.
Leprosy does not spread very easily. Transmission is poorly understood, but it is thought to occur via respiratory droplets. Leprosy cannot be contracted from a single exposure to someone with the disease, but only from prolonged exposure over many months. Leprosy cannot be transmitted sexually, and it cannot be passed from a pregnant woman to her fetus. Once an individual has begun treatment for leprosy, they are no longer contagious.
Not everyone who experiences prolonged exposure to leprosy will go on to develop the disease. There are both genetic and environmental factors that determine susceptibility. It is estimated that only 5-20% of people are susceptible to developing leprosy. Surprisingly, individuals with HIV infection do not appear to be at an increased risk of contracting leprosy nor at an increased risk for severe outcomes. The reasons for this remain unclear and are interesting when you consider their weakened immune system.
In addition to human reservoirs, leprosy has been found in armadillos, wild chimpanzees, mangabey monkeys, and British red squirrels. There are well-documented instances of humans contracting leprosy through contact with armadillos.
Symptoms of leprosy typically develop from 1 to 20 years after exposure, with an average incubation period of 5 years.  Leprosy often causes changes in skin color, with areas becoming hypopigmented or erythematous. Painless ulcers may be seen on the soles of the feet, and loss of eyebrows and eyelashes are sometimes noted. Subcutaneous nodules are also common.
In addition to the skin, leprosy affects the mucous membranes of the nose, throat, and eyes. Leprosy may cause congestion, nose bleeds, and sometimes collapse of the nasal septum, resulting in a characteristic “saddle nose deformity.” Other findings include difficulty in blinking, photophobia, corneal ulcers, staphylomas, and glaucoma. Untreated leprosy may result in blindness.
Leprosy can produce significant peripheral neuropathy. The skin may become numb to touch, pain, and temperature. Muscle weakness can occur, and paralysis of the hands and feet may be noted. Sometimes the disease causes nerves to become enlarged. Observation of enlargement of the great auricular nerve may lead to a diagnosis.
As the disease progresses, burning, tingling, and pain occur. The hands and feet may become crippled. Erosion of finger bones is sometimes seen, and toes and fingers may appear to be shorter as a result of reabsorption. Advanced disease may also cause erectile dysfunction, infertility, osteoporosis, and chronic kidney disease.
There are also psychiatric comorbidities associated with leprosy. One study found that 44% of patients with the disease suffer from depression, anxiety, or psychosis.
Two main systems have been used to classify leprosy.
Traditionally, the disease was categorized as “tuberculoid,” “lepromatous,” or “borderline.” Tuberculoid leprosy is usually limited to a few skin lesions. It is milder than lepromatous or borderline leprosy and is less contagious than the latter. Patients with tuberculoid leprosy mount immune responses that prevent the disease from progressing. In lepromatous and borderline leprosy, systemic infection is present. The skin, peripheral nervous system, and other organs may become involved.
More modern classification of leprosy divides the disease into two types: “paucibacillary” (PB) or “multibacillary” (MB). PB is defined as ≤ 5 skin lesions with no bacteria detected via biopsy. MB is defined by the detection of bacteria on biopsy or by the presence of ≥ 6 skin lesions.
The incidence of leprosy is declining, with approximately 200,000 new cases expected this year – worldwide.
It is estimated that currently, approximately 2 to 3 million people are living with disabilities secondary to leprosy.  It is commonly stated that leprosy is twice as common in men as women. The true discrepancy between the sexes remains unknown as sociocultural factors may have led to female cases being underreported.  Leprosy is more common in adults than children, and more common in older children than younger children.
Leprosy is extremely rare in the United States, with only 77 cases reported in 2019. The vast majority of these cases were imported, occurring in immigrants and refugees. Many countries in Europe reported zero cases in 2019.
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The diagnosis of leprosy generally begins with a clinical suspicion related to characteristic signs and symptoms. The gold standard for diagnosis is a biopsy of a suspicious area of skin or peripheral nerve also sometimes called a lepromin skin test. PCR has also proven to be a valuable tool.
In 2008, a second species, Mycobacterium lepromatosis, was also found to cause leprosy. Neither Mycobacterium lepromatosis nor Mycobacterium leprae has ever been successfully cultured under laboratory conditions. Both are obligate intracellular organisms, biologically related to the bacterium that causes tuberculosis.
In the 1940s, Promin was developed as the first effective treatment for leprosy. Promin is broken down by the body into Dapsone. In the 1950s, clinicians began using Dapsone itself as a treatment. Currently, Dapsone is rarely administered alone; and multi-drug regimens are more effective and may prevent the development of drug resistance.
Multibacillary disease is typically treated with daily Dapsone and Clofazimine – in addition to monthly Rifampin – administered for one year. Paucibacillary disease is typically treated with daily Dapsone plus monthly Rifampin for six months. Treatment may trigger severe inflammatory reactions. Anti-inflammatory drugs or medications such as aspirin, prednisone, and thalidomide are sometimes used to combat such episodes during treatment.
Throughout history, individuals affected with leprosy were discriminated against. In part, this was a reaction to the overt disfigurement seen in advanced cases. To this day, the expression “treated like a leper” refers to feeling ostracized.
The disease was referenced as a curse in the Bible and by the Ancient Greeks. In fact, the precise nature of the Biblical “leprosy” is not known. During the Middle Ages, “Leper Colonies” were built to isolate these patients, with as many as 19,000 such institutions existing across Europe. During the 19th century, hospitals known as “Leprosaria” emerged for patients with leprosy.
Despite the fact that leprosy is now curable, significant stigma regarding the disease remains. There are still 750 Leper Colonies in India, housing more than 200,000 people. In some cases, Indian law discriminates against people with leprosy, including a statute that permits the detention of leprosy patients. Hopefully, the stigma associated with leprosy will disappear from all countries. As long as discrimination remains, leprosy patients may avoid seeking treatment, and the disease will remain uneradicated.
GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools– GIDEON has you covered with a program that has met standards for accessibility excellence.
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