Leprosy is a highly stigmatized but curable infectious disease affecting the skin, eyes, respiratory system, and peripheral nerves. While roughly 200,000 patients are diagnosed with the condition annually, including about 200 in the US, most people have natural immunity. Infected individuals may lose feeling in their extremities and not notice cuts or burns, leading to severe infections and potential loss of affected areas.
It's also known as Hansen's disease for the Norwegian scientist Gerhard-Henrik Armauer Hansen, who discovered that leprosy is caused by the bacterium Mycobacterium leprae. (More rarely, a second bacterium causes leprosy.) Early leprosy symptoms, such as skin discoloration, may take 20 years to manifest, complicating tracking of disease transmission.
Public health authorities state the disease spreads through prolonged close contact and cannot be spread by touching or sharing a meal, but its exact mode of transmission remains unclear. Humans may also contract leprosy from armadillos. The disease has additionally been detected in wild chimpanzees and red squirrels.
Hours of research by our editors, distilled into minutes of clarity.
The standard approach for tracking disease transmission isn't realistic for this disease because symptoms may take decades to manifest. As a result, disease transmission is still not fully understood.
Contracting it requires prolonged contact with someone with the disease, meaning you'd have to be living with them. You cannot get leprosy from hugging someone with leprosy or sitting next to them. It's not known to pass from mother to fetus. The risk of transmission from armadillos is also likely low, but people should avoid touching wild animals for general safety.
The nerve damage that results from infection sometimes causes loss of feeling in extremities so injuries like cuts or burns may be missed. In such cases, resulting infections can lead to digit loss. Fingers or toes can also appear to shorten with this disease because nerve damage can sometimes make muscles in fingers and toes so weak that they're reabsorbed by the body.
Public health officials forcibly sent those diagnosed with leprosy to the Louisiana Leper Home in Carville, first founded in 1894. Listen to an interview about this site, its evolution, and how its residents advocated for themselves—including regaining the right to vote.
José Ramirez Jr. shares an account of his eight years at the 300-acre national leprosarium in Carville, Louisiana, from 1968 through the mid-1970s. Mostly staffed by nuns with nursing degrees, this facility was home to hundreds of people at a time, and it's also the site where they were required to be buried.
Untreated, the disease can lead to permanent nerve damage and the loss of sensation in arms, legs, and other extremities. The exact form of transmission remains unclear, but scientists suspect it is spread via respiratory droplets over a prolonged period. (Warning: Graphic content, including photos of deformities.)
Infection of the peripheral nerves—nerves outside the brain and spinal cord—is a known complication of leprosy. That damage can cause patients to lose their sense of touch and the ability to feel pain or temperature in affected areas, leading to accidental injury.
New research published in 2025 upended long-held notions that the disease was introduced to the Americas by European colonizers. Evidence of a lesser-known leprosy-causing bacterium was found in ancient human remains that date back 4,000 years.
Clinicians must screen for symptoms of eye and vision damage in leprosy patients, including loss of sensation, reduced blink reflex, and inability to close or keep the eyes closed.
The main leprosy-causing bacterium can't be grown in a petri dish, so the disease is challenging to study in the lab. For research purposes, it has been grown in the foot pads of mice.
Discover a broad spectrum of topics, from fundamental anatomy to the latest in medical research and treatments, all aimed at enhancing your understanding of health, wellness, and our bodies. Our resources are meticulously curated to offer precise and pertinent information to students, professionals, and anyone interested in learning more about the medical sciences. Dive in to stay informed, make well-informed health decisions, and explore the intriguing world of medicine.