Measles symptoms range from fever to pneumonia and encephalitis

Secondary complications from measles in children range across the whole body

The most serious effects of a measles infection, particularly in young children, come from its attack on the immune system. This leaves the whole body vulnerable to follow-on diseases, with some of the most serious including respiratory conditions, encephalitis, and more.

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.

The rare but deadly time bomb lurking after a measles infection

Subacute sclerosing panencephalitis, also known as Dawson disease, is a progressive and fatal neurodegenerative condition caused by a dormant measles infection. Typically, patients recover from measles normally, with the symptoms of SSPE only appearing years or even decades later. The incidence rate in unvaccinated pediatric patients is estimated to be around one in 1,300.

Measles is one of the most contagious preventable diseases

The virus’s ability to persist in the air for up to two hours means an infected person could enter a room, leave, and two hours later infect someone else entering the room. Its location in the body’s upper respiratory tract also makes it easy for viral particles to be sneezed or coughed into the air.

The measles vaccine has saved an estimated 94 million lives since its introduction

Measles killed an estimated 2.6 million people globally in 1980, after the development of a vaccine but before its widespread dissemination. By 2014, that figure had dropped to an estimated 73,000.

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.

Vitamin A does not cure measles, but it helps reduce the symptoms

Also known as retinol, vitamin A plays a significant role in supporting the body’s immune system. The virus attacks the immune system, and studies have shown a correlation between vitamin deficiency and severity of measles symptoms. Supplemental vitamin A doses are now a part of recommended treatment for pediatric patients.

Current US measles outbreak data from the CDC

This data portal from the Centers for Disease Control and Prevention tracks current cases, hospitalizations, and deaths from measles. A 2025 outbreak in Texas and New Mexico drove US cases to their highest levels since the early 1990s.

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.

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.

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.

Most cases of West Nile virus are asymptomatic in people

About 1 in 5 infected people develop symptoms from West Nile, including symptoms such as fatigue, head and body aches, and vomiting. But around 1% of patients develop severe complications such as encephalitis or meningitis, which can be life-threatening. Those who are most likely to become severely ill are people over age 60.

In 2012, a virus that causes HFMD may have killed dozens of kids in Asia

More than 50 young children in Cambodia died in spring 2012 for unknown reasons, but laboratory testing of samples available from a limited number of those children came back positive for Enterovirus 71. That virus, which can cause HFMD, is known to cause severe complications among some people who contract the disease. But health officials concluded that poor baseline health and then incorrect treatment using steroids helped exacerbate their condition, helping lead to the deaths.

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.

Hear what it's like to have malaria

In Kenya, as one malaria-sufferer explains, the disease is common enough that anytime a child has a fever or any sort of sickness families and the community will wonder if it's malaria. Sleeping under a mosquito net is recommended. Unfortunately, a gin and tonic will not keep malaria at bay.

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.

Sepsis is the leading cause of death in hospitals

Sepsis is the result of an overly aggressive immune system trying to combat infection, triggering inflammation throughout the body. After it begins, each passing hour increases the risk of death by 4% to 9%, and an estimated 350,000 people die from the condition in the US each year.

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.

MS disproportionately sickens women, but men tend to have worse outcomes

Though the disease is more common in women, men's symptoms progress more quickly, with men more often diagnosed with progressive MS and men's cases typically resulting in more severe symptoms—perhaps due at least partly to more delayed diagnosis—and more severe disability over time.

Improved 19th-century sanitation meant kids encountered polio later, with worse results

Almost all children likely used to contract poliovirus, but scientists suggest that when infants encountered it very early in life—due to poorer conditions and hygiene—they still had some maternal protection from pregnancy or through breastmilk, so the symptoms were more flu-like.

Ménière's disease is a long-term, inner ear disorder that causes vertigo

This severe vertigo-causing disorder may involve long and recurrent episodes of vertigo. Symptoms of this disease include balance issues and hearing loss, tinnitus, and a feeling of fullness in the ear. It typically affects only one ear and is linked to a buildup of excess fluid in the inner ear.

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.

Erythema migrans rash is common in Lyme—but it often doesn't look like a bull's-eye

The US Centers for Disease Control and Prevention states that this rash occurs in roughly 70% or more of Lyme disease patients, and typically occurs at the site of a tick bite. The rash may expand slowly over several days and feel warm to the touch, but it's rarely itchy or painful. As it grows, areas of it may clear—creating a target or "bull's-eye" appearance.

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

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.

Heat exhaustion is the most likely diagnosis if someone is talking clearly

Heatstroke, true to its name, looks more like a stroke. Its symptoms include severe disorientation, irritability, and seizures, among others. A patient does not need to have collapsed in order to have exertional heatstroke, but if someone is talking clearly, they likely have heat exhaustion, and it hasn't progressed to heatstroke.

Ebola infects and disables immune cells, triggering a cascade of events that leads to small blood clots throughout the body, weakening blood vessels and interrupting blood flow to key organs.

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

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

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

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.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

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.

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

Animal phobias are likely the most common type of phobias, followed by an extreme fear of heights.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

View the ten deadliest tornadoes in US history.

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

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.

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

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.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.

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.

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

A pickleball's loud 'pop' sound can reach 120 decibels, which is equivalent to a hammer hitting a nail

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

After her fellow cult members tried to kill her with an LSD-infused hamburger, one member of the Manson Family, the murderous cult led by Charles Manson, decided to testify against the group's leader.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

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

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.