Nerve axons become damaged by leprosy, so patients may lose feeling in their skin

Leprosy doesn't cause fingers or toes to fall off

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.

Leprosy affects the skin, eyes, and upper respiratory tract

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.)

Watch how doctors examine leprosy patients for signs of vision impairment

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.

About 95% of people are naturally immune to leprosy.

See examples of leprosy in the Bible—a broad term for skin ailments in ancient times

People afflicted with leprosy in the Bible may have had a range of different skin diseases, rather than what's clinically diagnosed as Hansen's disease (leprosy) today. In the Bible, as in many traditional societies, those with the disease were often considered unclean or sinful.

More than 200,000 people are diagnosed with leprosy annually

The disease still occurs in more than 120 countries. Brazil, India, and Indonesia continue to report more than 10,000 new cases annually.

Leprosy symptoms may appear 20 years after infection, so contact tracing isn't possible.

Up to 225 cases of leprosy in the US are diagnosed each year

Most cases in the US are imported, meaning someone was infected in a country where it was more common. Since symptoms can sometimes take decades to appear, tracing the origin of the disease can be hard.

People can—and have—contracted leprosy from armadillos

A 2011 study linked multiple human cases to the handling of armadillos or the consumption of their meat. The research couldn't document direct transmission, but did find that the animals and humans shared the same exact strain of the disease.

Leprosy bacteria are sometimes grown on mouse feet for research since the pathogens can't be grown in a petri dish.

81% of Florida's leprosy cases occur in central Florida, raising concerns

Researchers noted in 2023 that about one-fifth of new US leprosy cases were reported in the central part of the Sunshine State. What's more, about a third of the new US cases overall appear to have been acquired locally, raising questions about whether the disease is now naturally occurring in parts of the southeastern US.

Recent research indicates leprosy was present in the Americas before European settlers

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.

Listen to what it was like living as a medieval leper

This podcast uses paleopathological and anthropological findings to reconstruct what it was like for people diagnosed with leprosy in medieval times on the Eurasian continent. If a town lacked a leprosarium—an isolated leper asylum or colony—or the suspected leper was a foreigner or a Jew, which would make them ineligible for leprosarium admission, they'd be expelled.

See what regions report new leprosy cases

This graphic shows the burden of leprosy by region for 2023, based on data provided from the World Health Organization, which collates this information. Southeast Asia leads in the number of cases by region. (Some readers may experience a paywall.)

America had a national leprosarium—a leper colony—in Louisiana until 1999

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.

Leprosy bacteria replicate extremely slowly—only once every two weeks

Mycobacterium leprae has a long incubation period and a very slow replication rate, taking roughly 12 to 14 days to make a copy of itself and divide. In contrast, bacteria like E. coli can replicate in about 20 minutes in ideal conditions. Someone can be infected for years without experiencing any symptoms. This also makes the disease difficult to treat. This video describes the knowns—and unknowns—about this infectious bacterium.

Read excerpted accounts from some of the 8,000 residents with leprosy on Moloka'i

Accounts preserved by the Kalaupapa National Historical Park describe how residents felt about being sent to live in this remote location and knowing they would never be allowed to leave. In 2012, 20 residents with the disease continued to voluntarily live in the area.

Sclerosis is the technical term for the lesions or plaques that form without myelin

In the absence of myelin, the body forms scar tissue called sclerosis. That scar tissue hampers nerve's abilities to transmit nerve impulses, essentially acting as a roadblock to speedy communication.

Paralysis from polio occurs in under 1% of infections

About 1 in 200 cases of infection causes paralysis. For paralysis to occur, the virus travels from the throat, intestines, and gut to infect specific cells within the spinal cord and brain stem that control movements. Within hours of invading the nervous system, paralysis can occur. The virus can be present in bodily secretions and stool for multiple weeks post-infection.

Phantom limb pain may often match the pain or contortion of the injury that led to the limb loss.

Lupus, an autoimmune disease with varied symptoms, was named for wolf bite-like lesions

The 13th-century physician behind the name (lupus is Latin for wolf) named it after a patient he saw who had facial lesions that looked to him like a wolf's bite. Other common symptoms of the disease include extreme fatigue, painful and swollen joints, fevers, and light sensitivity.

Post-treatment Lyme disease syndrome may be caused by bacterial remnants in the liver

PTLDS, which refers to lingering symptoms of Lyme after antibiotic treatment, is an area of active research. Rodent research published in 2025 suggests that these ongoing symptoms may potentially be due to the body's inflammatory response to lingering cellular components from the bacteria that cause Lyme, Borrelia burgdorferi. In rodents, components of the bacteria's cellular wall may remain in the liver after the bacteria were eliminated with antibiotics.

Read an account of what life was like in America's national leprosarium—its leper colony

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.

Phantom limbs aren't just limited to limbs—there are phantom breasts, teeth, and more, and these sensations are often painful.

How ALS (Lou Gehrig's Disease) might work, and what scientists are learning about it

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that affects the nerve cells (neurons) controlling muscle movement. As the motor neurons degenerate, they stop sending signals to the muscles, causing progressive muscle weakness and, eventually, death. This three-minute animation focuses on the mechanisms within the motor neurons that cause them to degenerate. By understanding these mechanisms, researchers hope to one day find a cure for ALS.

When humans perceive touch, the information is sent to the thalamus and then to the primary somatosensory cortex, the part of the brain that receives sensory input.

Lyme disease is caused by bacteria transmitted through the bite of infected ticks

It's an infectious disease caused by Borrelia burgdorferi bacteria. It's spread through the bite of two species of infected ticks, the Western blacklegged ticks on the West Coast, and Blacklegged ticks found throughout the eastern US. The ticks can transmit the disease at both the nymph and adult stage. It's not known to be transmitted from one person to another via kissing or sex.

Research suggests the brain maintains connections to lost limbs

Decades-old research suggested brain reorganization after amputations, but brain scans show unchanged limb representations. Phantom limb pain may result from such unchanged brain maps, which may enhance prosthetic limb control in brain-computer interface technology.

Leprosy has been detected in British red squirrels

The animals have been infected with both strains of the bacterium that cause leprosy. Researchers have found that squirrels living in different parts of the UK were infected with different species of the disease-causing bacteria. (Some users may experience a paywall.)

Rabies is nearly 100% fatal once symptoms appear

Rabies, a viral disease attacking the central nervous system, is nearly always fatal once symptoms appear. It spreads through the infected animal saliva (typically through bites) and causes encephalitis, leading to severe neurological symptoms and death. See how the lyssavirus—the bugs behind rabies—work once inside the body.

Being struck by lightning has a mortality rate of about 10%

Near-immediate deaths are the result of electrical disruptions in the heart and nervous system, causing cardiac arrest, but severe skin burns, temporary paralysis, and blown eardrums are more common. About 74% of survivors are left with a long-term disability, which includes brain damage and changes in memory and mood.

Nonamputees can be tricked into thinking they have phantom limbs with rubber arm experiments.

Measles infection can cause long-term immune system “amnesia”

The measles virus attacks the body's immune system, including preying on T and B cells in the lymphatic system. These cells hold memories of past infections, which can be degraded as the virus destroys them. This leaves patients susceptible to other infections for a year or longer.

In 2011, a mysterious illness spread around LeRoy, New York

A handful of girls were stricken with bizarre twitches, tics, and spasms — all apparently involuntary. Some believed the incident to be conversion disorder, an illness where emotional troubles have physical symptoms.

Wild chimpanzees have been spotted with leprosy lesions

In research published in 2021, scientists reported discovering cases of leprosy in wild chimpanzees from Guinea-Bissau and the Ivory Coast—marking the first time the disease has been found in any nonhuman species in Africa. They confirmed that leprosy was the cause of the deformities by testing the animals' poop for the presence of the disease-causing bacteria.

A web of sensory neurons in the skin help filter out background sensations

The somatosensory system helps us organize and navigate our surroundings, enabling us to understand our bodies in relation to our environment and also filter out minor sensations that are basically background noise so they aren't overwhelming to our bodies. Meanwhile, viscerosensation—or internal sensation—refers to the internal sensory neuron system that conveys information from internal organs to the brain.

A rare measles complication is that the virus can linger in the body for years after apparent recovery and continue to replicate—leading to a progressive and fatal breakdown of the central nervous system that can occur decades after the initial infection.

Nonwhite Lyme patients tend to be diagnosed later and have more severe disease

Peer-reviewed research published in 2025 from Pfizer—a pharmaceutical company working on a candidate vaccine for Lyme disease—examined Lyme data from more than 150,000 Medicare and Medicaid beneficiaries and found that Black patients, as compared to white beneficiaries, were more likely to have disease that had spread further throughout the body at the time of care. The difference, the scientists wrote, may be partly due to difficulties recognizing the characteristic rash on darker-colored skin.

Remylination is a huge focus for treatment—especially among older adults

Our ability to build new myelin sheaths for nerves degrades with age. There have been research advances boosting cells that support these processes and clear away debris from degraded myelin, but not yet any medications to boost myelination itself, which would aid nerve signaling and preserve nerve function.

What is the peripheral nervous system?

This nervous system extends throughout the body, where it acts as the informational bridge between the central nervous system, housed in the brain and spinal cord, and the body's muscles and organs. The peripheral nervous system is further divided into the autonomic, enteric, and somatic nervous systems, each of which oversees certain muscle types and processes. This article overviews the anatomy and functions of the peripheral nervous system.

Itching is caused by stimulated nerve cells in the skin

Scratching produces low-level pain signals to the brain, distracting from the itch. Scratching also releases serotonin, a neurotransmitter that creates a happy sensation, which resets the itch signal. This can cause a cyclical itch-scratch cycle.

Changes in vision or eye pain can be early MS symptoms

This occurs due to myelin degradation around the optic nerve, impairing its ability to transmit visual information to the brain. Individuals may especially experience eye symptoms after exercising or taking a hot shower because boosted body temperatures slow down nerve function in nerves already damaged by MS.

Measles symptoms range from fever to pneumonia and encephalitis

While less common, most measles-related deaths come from secondary conditions such as pneumonia (one to six cases per 100 patients) and encephalitis (one case per 1,000 patients). Blindness, which is rare, may arise from corneal ulceration.

Herpangina is a related disease that also has characteristic sores in the mouth and throat

This painful condition is also caused by several viruses in the enterovirus family. The condition typically has early symptoms including a fever and sore throat, in addition to the sores. Herpangina is often mistaken for strep throat, but there's no cure for herpangina and patients typically have symptoms for about a week.

Electricity can be lethal because it can disrupt the nervous system, which controls critical bodily functions that rely on electrical signals between cells, such as breathing and heart rate.

Multiple sclerosis means 'many scars'

That's a reference to the scarring or lesions that occur in the brain, spinal cord, and elsewhere whenever the immune system has a flare-up. The immune system attacks the myelin because it incorrectly responds as if it's a threat, damaging the body's ability to transmit electrical signals effectively from areas of the body to the brain.

Touch deprivation can heighten anxiety and depression

Pacinian Corpuscles are pressure receptors just under the skin that send signals to the vagus nerve in the brain—that's the cranial nerve which regulates involuntary actions like breathing, heart rate, and the general "fight or flight" response. Activating those receptors can slow the heart, decrease blood pressure, and lead to the release of oxytocin and cortisol. The absence of touch, conversely, can promote negative feelings.

Individuals with synesthesia experience involuntarily overlapping sensations

Tasting words or seeing colors in music results from the brain retaining extrasensory connections from infancy. While most lose these neural pathways during development, about 4% of people are synesthetes, maintaining them without realizing it's unusual.

Mind-controlled bionic arms use nerve implants to restore sensation and movement

Unlike traditional prosthetics that rely on surface electrodes or mechanical parts, this system uses implanted titanium and nerve-connected electrodes to enable a seamless brain-to-arm connection. Patients train in virtual reality with their implanted signals before using the physical prosthesis.

Chronic lyme isn't a medically recognized diagnosis in conventional medicine

It describes a constellation of symptoms attributed to a persistent Lyme infection—meaning the bacteria have remained present even after antibiotics. It often occurs among people who have never received a positive test for Lyme. Doctors do recognize "post-treatment Lyme disease syndrome," however, which can include muscle and joint pain, fatigue, and cognitive difficulties after treatment for confirmed Lyme.