Measles is one of the most contagious preventable diseases

Measles attacks the body’s immune system, leaving it vulnerable to secondary complications

A measles infection begins in the lungs, where it hijacks cells known as macrophages and begins to replicate itself. It then uses a Trojan horse method to enter the lymph nodes, where it attacks vulnerable T and B cells. Symptoms include fever and rashes.

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.

The R0 value is how epidemiologists quantify disease contagiousness

The basic reproduction number indicates the average number of people a person with a disease will infect. Measles is the most contagious disease, with an R0 of 12-18, though vaccines have significantly reduced the number of susceptible individuals.

Measles evolved from an ancient cattle disease as early as 3,000 years ago

Genetic analysis suggests that the closest modern relative of measles is a livestock virus known as rinderpest, with the viral strains diverging between 2,000 and 3,000 years ago. The timing coincided with the rise of major cities above 250,000 people, offering a novel transmission route for the newly mutated measles virus.

A 1954 outbreak at a Boston boarding school allowed scientists to isolate the measles virus

While measles was described as early as the 9th century, humanity lacked the medical technology to fight the disease until the mid-20th century. Vaccine development from the Boston outbreak in the 1960s and 1970s led to one of the most effective inoculation campaigns in history.

Measles was declared eliminated in the US in 2000

Following a decades-long vaccination campaign, health officials declared victory over measles. This formal definition does not mean limited outbreaks no longer occur, but that ongoing endemic transmission for longer than 12 months has been prevented.

A technical look at the measles virus and its life cycle

The measles virus is made up of a single strand of RNA, packaged inside an envelope that varies in shape and size. A negative-sense paramyxovirus—the same family as mumps—the virus is encased in proteins that help it attach to immune cells inside the body.

Measles reached global transmission during the 15th- and 16th-century Columbian exchange

Devastating diseases like smallpox, influenza, measles, and other viruses were largely introduced into the Western Hemisphere beginning with the 1492 arrival of Christopher Columbus and the ensuing age of exploration.

A look at the 2025 measles outbreak in West Texas and surrounding areas

A measles outbreak in the summer of 2025 ultimately led to more than 900 cases and the deaths of two young children. The highly contagious virus requires vaccination rates near 95% to achieve herd immunity—the Texas outbreak spread through areas of significant mistrust of vaccines, including the area’s Mennonite community.

Flu spreads through droplets in the air and on surfaces

Influenza passes mainly through tiny droplets released when sick people cough, sneeze or talk. The virus can also survive briefly on surfaces, allowing it to spread when others touch contaminated objects.

HFMD can survive on surfaces for days at a time

That's why the virus can be transmitted via fomites—surfaces that have virus on them like doorknobs, kids toys, etc. These viruses are resilient—they are often even resistant to freezing (and are frequently stored at freezing temperatures in lab settings).

Polio commonly spreads when virus-laden feces gets into our mouths

This highly infectious disease is transmitted from one person to another, mainly when we eat virus-laden poop particles. Less frequently, contaminated food or water can transmit the virus, or people can be infected via respiratory droplets (from coughing or sneezing).

The CDC’s “Pink Book” chapter on measles

The agency’s “Pink Book” is meant to be a comprehensive guide on various diseases and their treatments. This chapter on measles reviews how it works and common symptoms, and provides information on the MMR and MMRV vaccines.

Variola: the second-deadliest virus on Earth

Because it was declared eradicated in 1980, many forget smallpox is one of history's deadliest diseases—in its final century, it's estimated to have claimed 500 million lives. This 11-minute video from production studio Kurzgesagt takes a look at...

Hand, foot, and mouth is usually seasonal—peaking in summer—but not always

This painful, contagious disease most commonly has outbreaks in summer and early fall in the US because the enteroviruses that cause disease can most readily survive and be transmitted in warmer, humid conditions. It can still show up throughout the year, however.

What is a sneeze? (And can it kill you?)

A sneeze is an important involuntary reflex to expel something that is irritating your nose. But can it kill you? No, say these silly video hosts. Although, the sneeze can expel air, saliva, and mucus at nearly 100 miles per hour in a five-foot radius. See them break it down with this quick, quirky video.

Marburg virus, related to Ebola, is also extremely deadly, and has no available vaccine.

Cryptococcus neoformans, a growing threat, causes infections in the brain and lungs

This inhalable, microscopic pathogen is found worldwide. It rarely causes illness, but it can take root in those with compromised immune systems, including people with advanced HIV/AIDS. Symptoms of cryptococcal infection—such as a stiff neck, vomiting, and confusion—can begin weeks or months after breathing in spores, though sometimes symptoms won’t appear for years. There are no known cases of transmission between people or between people and animals.

Why we don't have an answer for the common cold

Since a landmark study of the common cold in 1925, researchers have learned much more about the seasonal ailment. Despite continuous study, people still contract colds for similar periods of time at the same rate with the same symptoms, and there's no vaccine. This article explains how the many viral strains make it hard to control.

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

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.

Bats are uniquely suited to act as reservoirs of viruses

Some of the deadliest diseases to jump from animals to humans originate in bat species. This rich visualization explores the diversity of bats and the factors that make them efficient vectors for harboring and transmitting disease, from their long lifespans to their migration patterns.

Explore what it's like Inside a patient isolation unit

Containing a contagious disease like Ebola requires strict protective measures. There are several specialized medical wards to contain deadly infectious diseases at hospitals across the U.S. Emory University has one such unit, where 4 patients were treated during the 2014 outbreak.

Particles found in Martian air pose significant risks to human lungs

Ultrafine dust, just 3 micrometers wide, is small enough to bypass lung defenses and enter the bloodstream, where its highly reactive chemicals can cause thyroid disease. Silica in the dust can also cause silicosis, a chronic and incurable lung disease.

Drug-resistant staph infection is one of the deadliest superbugs

Methicillin-resistant Staphylococcus aureus (MRSA)—the superbug version of staph infection—is responsible for more deaths than any other superbug, killing more than 120,000 people globally each year. The bug is leading cause of hospital infections, and is harmless on the skin but causes severe symptoms once inside the body.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

Broken or neglected air conditioners are risky for respiratory health

A well-maintained air conditioner can typically keep out unwanted pathogens, but units that are dusty or water-logged can foster germs and cause harm. AC units also remove moisture from the air, potentially causing mucus membranes to dry out and become vulnerable to infection.

Fear (and stress) can be contagious via pheromones secreted by the body

While seeing someone else in a panicked state may induce a stress response, researchers have found stress can be literally contagious—chemicals contained in sweat and other secretions can trigger stress hormone release in others. Theories suggest this feature is an evolutionary adaptation to protect groups from danger.

Explore what it's like inside a patient isolation unit, used in situations such as treating a patient or suspected patient with Ebola.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

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.

Tattoos remain visible on your skin thanks to immune cells called macrophages

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.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Elk Cloner, the first computer virus to spread in public, was written as a practical joke by Richard Skrenta, a Pittsburgh high school student.

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

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

View the ten deadliest tornadoes in US history.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

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

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

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

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.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

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

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time