Learn how cholera bacteria sicken humans

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 1892, two scientists purposefully infected themselves with cholera bacteria

When they became ill—one with mild diarrhea and the other with severe cholera—researchers pointed to that as proof that the pathogen caused the disease.

See how cholera spreads in a community

This animated video offers a comprehensive look at how cholera spreads. It makes clear why it's so difficult to stamp out this disease in communities around the world. It also details what steps can help control cholera.

Cholera can persist in the environment, unlike smallpox, which needs a human host

Vibrio cholerae is the pathogen that causes cholera. It can reproduce in the environment without a human host, which means it's formally called a facultative pathogen. Obligate pathogens need a host to reproduce. Examples of obligate-based diseases include leprosy and smallpox.

1 in 4 people around the world don't have access to clean water

Poor water sanitation puts people at risk of acquiring this diarrheal infection. Cholera infections are on the rise due to extreme weather events and conflict. In recent years there have been cholera outbreaks in locations that hadn't seen the disease in many years, including Haiti.

The wonderfully named Vibrio diabolicus is a cousin of the cholera-causing bacterium

This bacterium, which belongs to the same genus as the cholera bacterium, was initially isolated from deep-sea hydrothermal fields. It was sampled from water that was scooped up during a French-American cruise in October 1991.

More than 4,000 people died from cholera in 2023

This global health threat sickened more than half a million people in 2023 and killed 4,007 people. That's a 71% increase in deaths as compared to a year earlier. (Report only offered in PDF format.)

Extreme weather conditions heighten cholera risks in settings like refugee camps

Runoff from sewage—exacerbated by situations like flooding or extreme rains—heightens this threat. Increasing temperatures also create the ideal conditions for the bacteria to reproduce, increasing transmission risks.

Maryland required cholera researchers to fly a yellow warning flag—signifying quarantine dangers in the 1970s

University of Maryland Hospital researchers intentionally infected volunteers with the cholera bacterium in the late 1970s to further their understanding of the disease. They proceeded with this work following the recommendation of a US government panel. (Some users may encounter a paywall.)

We're in the middle of a decadeslong cholera pandemic

In 1961, the world's seventh recorded cholera pandemic started in South Asia, and it has continued through the decades. India and Bangladesh are at particular risk. This pandemic is driven partly by conflict, population displacement, extreme weather, and poor water infrastructure.

Cholera went global thanks to global trade

The first cholera pandemic grew from an outbreak in India, in 1817. Scientists suggest it spread from there throughout the continent and onward to Africa, Russia and Europe through the poop of traders.

Cholera vaccines can protect people from disease for months—or even years

There are three recommended cholera vaccines on the market. The number of required shots and the period of protection they provide vary, but each of them can be life-saving.

The cholera bacteria was first isolated in 1854—but the discovery was largely ignored

The pathogen was isolated by the Italian physician Filippo Pacini in Florence, Italy, though his discovery was largely ignored in favor of the popular miasma—bad air—theory of disease at the time. The pathogen was separately isolated about three decades later by German microbiologist Robert Koch.

Historically, cholera has repeatedly disrupted the Hajj for Muslims

Outbreaks of the disease throughout the 19th century and the beginning of the 20th, killed thousands of religious pilgrims as they sought to complete this obligatory pilgrimage.

Cholera was called the 'Blue Death'

In the mid-1800s—when John Snow identified cholera in London—the disease was known simply as the "Blue Death." That's because blood would thicken in patients' veins when they were struggling with extreme dehydration. As a result, their skin would turn a blueish hue as their blood was starved of oxygen.

Explore these images to better understand why food poisoning makes you feel nauseous.

The canal carried germs as well as goods

In 1832, North America’s first cholera epidemic spread inland by way of the Erie Canal, carried by immigrants arriving on ships. Fearful towns barred passengers from disembarking, yet cholera, smallpox, and other diseases still traveled the waterway.

Unprecedented imaging of the Vibrio bacteria, published in 2026, may highlight new treatment targets

Researchers have produced the most detailed image ever of a key part of the Vibrio bacteria—the cause of cholera—known as the sheathed flagellum, which helps it move.

Oral rehydration solution was developed in the 1960s in response to cholera deaths.

Watch what the Ebola virus does inside the body in order to spread and survive.

Robert Koch won the Nobel for his tuberculosis work, but he also pioneered cholera research

Koch was one of the first scientists to isolate the bacterium that causes cholera while investigating an outbreak in Egypt in 1883. He went on to advise about rules to control cholera outbreaks, which formed the basis of the disease control approaches and water hygiene techniques still used today.

Pooping or puking out pathogens is sometimes recommended with food poisoning

Sometimes stopping food poisoning-linked diarrhea with over-the-counter medications is a bad idea because it may prolong illness. Doctors can advise you if your diarrhea or vomiting is severe about what medications to take and when, but generally doctors recommend trying to stay hydrated during a bout of food poisoning and letting the body naturally remove pathogens from the body via vomiting or diarrhea, as needed.

We can get food poisoning from spending time in swimming pools, lakes, rivers, and ponds

Some of the same pathogens that may sicken us in food or water may also sicken us in recreational swimming environments. Bacteria can rub off of people’s (or animal’s) bodies or contaminate the water through a diarrheal episode. Washing your hands for at least 20 seconds before eating food if you are at the beach, pool, or other similar environments and being sure not to swallow the water are ways to help keep safe.

Ebola virus, with an average fatality rate of around 50%, has been responsible for more than 2,000 confirmed deaths during the 2026 outbreak in the Democratic Republic of the Congo and Uganda.

Although rare, HFMD can spreads in pools due to poor bathroom hygiene

In pools with inadequate levels of chlorine, this disease can spread via the poop-to-mouth route, though this isn't one of the most common ways the disease is transmitted. People can become infected by swallowing contaminated pool water after little kids (or their parents) don't do an adequate job removing virus-laden feces from the child before the child enters the water.

Lengthy incubation periods are why it's tough to link foodborne illness to specific foods.

This is what happens inside your body when you're sick

This video details the biology of what happens inside the human body during illness.

What happens when the gut microbiome is out of whack?

An imbalance in gut microbiome flora can lead to a condition known as dysbiosis. This condition is typically characterized by a drop in microbiota diversity and an increase in harmful unicellular and acellular organisms, such as viruses, that can negatively impact the host's immune system and overall health. Genetics, infections, dietary choices, antibiotics, food additives, artificial sweeteners, and other lifestyle and environmental factors can cause dysbiosis.

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 'kissing bug disease' occurs when a bug's parasite-laden poop gets into your blood

Chagas disease transmission can occur when triatomine bugs bite someone infected with a Trypanosoma cruzi parasite and then bite someone else, passing on the pathogen, though the parasite can also be transmitted in other ways, including via food, congenitally, and through blood transfusions. The bugs tend to feed at night and can bite anywhere on the body, but their reputation for biting people around the mouth and eyes created the idea that the bugs were "kissing" humans. Recent research suggests the disease may be endemic in the US.

Fecal transplants can help treat infections by transplanting healthy gut bacteria from a donor into a patient's gastrointestinal tract using samples of human waste, which are turned into a liquid mixture and often delivered via a colonoscopy procedure.

There's a goddess in South Asia worshipped for her protection against cholera

Both Hindus and Muslims in certain parts of South Asia pray to Oladevi, also known as Olabibi, to help protect against cholera. People also pray to this goddess for protection against epidemics more broadly.

There's an official term for the sound your stomach makes before intense diarrhea

It's borborygmi. The sound is produced when gas or liquid moves through the bowel. Peristalsis, the wave-like muscle tightening process that typically pushes food through the digestive system, produces the sound as it tries to push these substances through the body.

Accidental ingestion of batteries can be life-threatening

Tissue in the body can serve as a circuit path between the anode and cathode of a battery, resulting in electrical burns and gradual tissue erosion. Stomach acid can corrode a battery and cause its toxic contents to leak, making a person sick. Batteries for internal use, such as in pacemakers, require special designs.

Legionnaires' disease is a serious lung infection caused by Legionella bacteria, and it's often contracted from inhaling contaminated mist or water.

Food poisoning can sometimes cause serious long-term health issues

Although foodborne illness can be relatively mild and cause short-term discomfort, more rarely it can also cause long-term severe health consequences, depending on your individual risk factors, the severity of your sickness, and the care you receive. Kidney failure is one serious complication associated with certain types of food poisoning. Meningitis, hepatitis, arthritis, and pancreatitis are also rare and serious foodborne illness complications. If a pregnant person gets food poisoning, it can cause health issues for the fetus.

See how the Ebola virus affects blood circulation in the human body.

Harmful algal blooms can occur in warm, nutrient-rich, stagnant waters and are often associated with the rapid reproduction of blue-green algae—a misnomer for cyanobacteria, not algae.

See the incubation periods for certain food poisoning-causing organisms

Read this chart that lists common food sources of different foodborne illness-causing pathogens and typical times between exposure and symptom onset.

Without liver bile, human poop would be a pale silver color

Stomach acid and enzymes break down food into smaller particles, expelling a semi-fluid mass called chyme into the small intestine, where bile is added. As the intestines absorb nutrients and water, the chyme solidifies and changes color.

Natural toxins produced on plants or consumed by animals may cause food poisoning

When humans eat plants with certain natural toxins on them—including a family of toxins called aflatoxins that fungi produce on crops like peanuts and corn— they can become ill with food poisoning. Toxins can still harm humans even if animals or plants appear fine to the human eye. The World Health Organization advises that we should throw away moldy or discolored foods, refrain from eating wild plants or mushrooms that aren’t definitively nonpoisonous, and remember that just because something is “natural” it’s not always safe to eat.

John Snow—not the one from 'Game of Thrones'—determined that contaminated water sickened London

His pioneering epidemiology work during an 1854 cholera outbreak mapped out the commonalities between people in London who were getting sick. He discovered that ill people were getting water from the same Broad Street pump. Before Snow's work, the prevailing theory was that bad air sickened individuals instead of cholera-causing bacteria in the water.

Explore inside a mosquito factory where millions of mosquitoes are bred weekly

In Medellin, Colombia, scientists are infecting Aedes aegypti mosquitoes with Wolbachia, a bacterium that wouldn't otherwise infect the species, but does block its ability to transmit dengue, Zika, yellow fever, and chikungunya. In the wild, infected mosquitoes would breed with wild mosquitoes, pass down Wolbachia, and thus reduce disease transmission.

Climate shifts are projected to cause more cases of food poisoning

Research published in 2024 suggests that with more severe heatwaves and natural disasters, scientists expect there to be a rise in foodborne disease, especially in Africa and Asia. Already, there are an estimated 600 million food poisoning cases and 420,000 deaths annually. Diarrhea is the most common cause of those deaths.

Bacteriophages—viruses that infect bacteria before multiplying within them—exist on Earth in numbers greater than all other living organisms combined.

See this graphic of the complex malaria transmission lifecycle.

Norovirus is the leading cause of food poisoning in the US

The illness is typically transmitted when virus-laden feces gets into another person’s mouth. That occurs when people do not properly wash their hands, contaminating food or surfaces.

Learn about swimmer's ear, which sickens 1 in 10 Americans

This outer ear infection—in the tube leading from the ear opening to the eardrum—is usually caused by bacteria. Formally called otitis externa, this condition is commonly called swimmer's ear because microbes can enter the ear canal while swimming.

Although consuming saltwater can dehydrate and kill organisms, some fish survive by using specialized gills that leach excess salt from their bodies back into the surrounding water.

The history of germ theory, which explains that illnesses are caused by microorganisms

For centuries, the miasma theory, which held that illnesses were caused by clouds of "bad air" produced by decaying organic matter, was the accepted explanation for the spread of disease. The development of microscopes and the subsequent technology to isolate bacteria and test disease spread in mice greatly contributed to contagionists overturning miasmatists.