More than 200,000 people are diagnosed with leprosy annually

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.

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.)

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.

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.)

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

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.

About 95% of people are naturally immune to leprosy

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.

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.

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.

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.

More than 1 in 7 people worldwide have had Lyme disease

Research published in 2022 suggests that 14.5% of the world's population has contracted Lyme disease. Researchers arrived at that estimate by analyzing the presence of Lyme disease antibodies (indicating prior infection) across 89 studies conducted between January 1984 and December 2021. The works collectively included blood samples from more than 150,000 people. (Some user may encounter a paywall.)

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.

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.

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.

Neglected tropical diseases affect more people than the population of Europe

This group of conditions, which includes hookworm, sickens roughly one in seven people on the planet—a tally which dwarfs Europe's population of roughly 450 million. International cooperation and donations are helping to control some of these illnesses, which can be caused by parasites, viruses, and bacteria. They're all treatable or preventable, but primarily occur among poor, isolated communities that may not receive adequate care.

Treating black fever can result in a complication that spreads the deadly disease

Black fever, a deadly parasitic disease second only to malaria, threatens more than 1 billion people across more than 83 countries. Also known as kala-azar or visceral leishmaniasis, the disease is caused by parasites that spread through sandfly...

Since 1600, the longest stretch without an outbreak that killed 10,000 was four years

We think of pandemics as unlikely events, but disease outbreaks are surprisingly common. Over the past 400 years, the longest stretch without an outbreak that killed at least 10,000 people was just four years. The next pandemic can't be precisely known, so experts and policymakers focus on preparation.

Influenza infects up to a billion people worldwide each year

The World Health Organization estimates that seasonal influenza causes about 1B cases annually, including 3 to 5M severe illnesses and between 290,000 to 650,000 deaths.

Rabies kills more than 50,000 worldwide each year

Rabies transmission to humans typically comes from an infected animal, and death was very common before recent protocols were developed (post-exposure prophylaxis). The virus is neurotropic, which means it has an affinity for nerve tissue, and moves quickly from broadly infecting the body to destroying the brain.

Polio is currently circulating in only two countries but it remains difficult to eradicate

Wild polio virus is only endemic in two places. Afghanistan and Pakistan are the last two countries with naturally occurring polio cases. Vaccination campaigns have been plagued by misinformation, Taliban bans on vaccines, distrust of public health workers, and violence, including the killing of vaccinators.

China reports the highest prevalence of hearing loss and South Africa reports the lowest

This conclusion comes from research published in 2025 that analyzed self-reported hearing loss and hearing aid use from long-term studies that covered 28 countries. Its findings included that the countries with the greatest prevalence of hearing loss (China, South Korea, Mexico, and Brazil) also had the lowest levels of hearing aid use.

Explore more statistics about cancer

The American Cancer Society's Cancer Statistics Center estimates there will be more than 2 million new cancer cases and almost 620,000 cancer deaths in the US during the course of 2025. Breast, prostate, and lung cancers remain the most prevalent. This interactive tool provides detailed statistics on cancer incidence, mortality, and survival rates, allowing users to explore data by state, cancer type, demographics, and risk factors.

The 2026 Ebola outbreak is hampered by a lack of vaccine against the species of the virus, heightening the need for rapid tests to aid in disease control.

About 20% of people infected with cholera have severe symptoms

That's according to studies from outbreaks in Bangladesh. Most people who contract the disease have mild or moderate symptoms, or none at all. Yet anyone infected with the disease-causing bacteria can shed the pathogens in their feces for a few days, or even up to around 10, seeding the environment with bacteria.

In 2024, Black Friday was observed in 129 countries

Brazilians adopted Black Friday in 2010. Today, 60% of Brazilians participate in the shopping event. Large corporations offering Black Friday sales in the US (like Amazon, for instance) began offering similar deals in places like the UK, spreading the holiday internationally.

Most of the world’s population has difficulty processing lactose—but that’s not an allergy

Lactose intolerance is a digestive condition that occurs when the small intestine has difficulty breaking down lactose, a sugar found in products like milk or cheese, leading to symptoms such as diarrhea or bloating. Almost 70% of the world’s population may have lactose processing issues, particularly in Asia and Africa. This is different from a condition called cow's milk protein allergy—an immune system disorder that can cause hives and anaphylaxis.

Obesity rates have more than doubled worldwide since 1990

In the US alone, the percentage of the population meeting the clinical standard of obesity rose from less than 20% to more than 40% over the past three decades. This rise has been matched by many countries across the globe, from industrialized to developing nations.

Between 10 million and 50 million people in the US develop rashes from poison ivy, poison sumac, and poison oak each year.

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

This real-time tracking of the hantavirus cruise ship outbreak in May 2026 offers a unique glimpse into the global reach of the outbreak and whether the virus sickened passengers and their communities around the world.

Louisiana's 'Cancer Alley' is infamous for having some of the highest industrial pollution, toxic air emissions, and cancer risks in the US.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

In 2018, 26-year-old missionary John Allen Chau was killed by tribesmen after attempting to reach and evangelize on India's isolated North Sentinel Island

Telehealth demand for GLP-1s for weight loss is booming as consumers seek easier access.

Fireworks-related ER visits are on the rise—in 2024, they increased by 52% as compared to the prior year.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

In 2019, a laptop loaded with six of the worst malware in history and described as 'an exhibit of historical weaponry' sold for $1.3M.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by more than 1.5 million Muslims each year.

Despite being favored by 87% of Americans, Congress does not have term limits.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in terms of casualties, forces mobilized, and displacement of civilians.