Most people exposed to the cholera bacterium (Vibrio cholerae) don't become ill and never know they've been infected. Yet because they shed cholera bacteria in their stool for seven to 14 days, they can still infect others through contaminated water. Most symptomatic cases of cholera cause mild or moderate diarrhea that's often hard to distinguish from diarrhea caused by other problems.
Only about 1 in 10 infected people develops the typical signs and symptoms of cholera, usually within a few days of infection.
Symptoms of cholera infection may include:
- Diarrhea. Cholera-related diarrhea comes on suddenly and may quickly cause dangerous fluid loss — as much as a quart (about 1 liter) an hour. Diarrhea due to cholera often has a pale, milky appearance that resembles water in which rice has been rinsed (rice-water stool).
- Nausea and vomiting. Occurring especially in the early stages of cholera, vomiting may persist for hours at a time.
Dehydration. Dehydration can develop within hours after the onset of cholera symptoms. Depending on how many body fluids have been lost, dehydration can range from mild to severe. A loss of 10 percent or more of total body weight indicates severe dehydration.
Signs and symptoms of cholera dehydration include irritability, lethargy, sunken eyes, a dry mouth, extreme thirst, dry and shriveled skin that's slow to bounce back when pinched into a fold, little or no urine output, low blood pressure, and an irregular heartbeat (arrhythmia).
Dehydration may lead to a rapid loss of minerals in your blood (electrolytes) that maintain the balance of fluids in your body. This is called an electrolyte imbalance.
An electrolyte imbalance can lead to serious signs and symptoms such as:
- Muscle cramps. These result from the rapid loss of salts such as sodium, chloride and potassium.
- Shock. This is one of the most serious complications of dehydration. It occurs when low blood volume causes a drop in blood pressure and a drop in the amount of oxygen in your body. If untreated, severe hypovolemic shock can cause death in a matter of minutes.
Signs and symptoms of cholera in children
In general, children with cholera have the same signs and symptoms adults do, but they are particularly susceptible to low blood sugar (hypoglycemia) due to fluid loss, which may cause:
- An altered state of consciousness
When to see a doctor
The risk of cholera is slight in industrialized nations, and even in endemic areas you're not likely to become infected if you follow food safety recommendations. Still, sporadic cases of cholera occur throughout the world. If you develop severe diarrhea after visiting an area with active cholera, see your doctor.
If you have diarrhea, especially severe diarrhea, and think you may have been exposed to cholera, seek treatment right away. Severe dehydration is a medical emergency that requires immediate care regardless of the cause.
A bacterium called Vibrio cholerae causes cholera infection. However, the deadly effects of the disease are the result of a potent toxin called CTX that the bacteria produce in the small intestine. CTX binds to the intestinal walls, where it interferes with the normal flow of sodium and chloride. This causes the body to secrete enormous amounts of water, leading to diarrhea and a rapid loss of fluids and salts (electrolytes).
Contaminated water supplies are the main source of cholera infection, although raw shellfish, uncooked fruits and vegetables, and other foods also can harbor V. cholerae.
Cholera bacteria have two distinct life cycles — one in the environment and one in humans.
Cholera bacteria in the environment
Cholera bacteria occur naturally in coastal waters, where they attach to tiny crustaceans called copepods. The cholera bacteria travel with their hosts, spreading worldwide as the crustaceans follow their food source — certain types of algae and plankton that grow explosively when water temperatures rise. Algae growth is further fueled by the urea found in sewage and in agricultural runoff.
Cholera bacteria in people
When humans ingest cholera bacteria, they may not become sick themselves, but they still pass the bacteria in their stool. When human feces contaminate food or water supplies, both can serve as ideal breeding grounds for the cholera bacteria.
Because more than a million cholera bacteria — approximately the amount you'd find in a glass of contaminated water — are needed to cause illness, cholera usually isn't transmitted through casual person-to-person contact.
The most common sources of cholera infection are standing water and certain types of food, including seafood, raw fruits and vegetables, and grains.
- Surface or well water. Cholera bacteria can lie dormant in water for long periods, and contaminated public wells are frequent sources of large-scale cholera outbreaks. People living in crowded conditions without adequate sanitation are especially at risk of cholera.
- Seafood. Eating raw or undercooked seafood, especially shellfish, that originates from certain locations can expose you to cholera bacteria. Most recent cases of cholera occurring in the United States have been traced to seafood from the Gulf of Mexico.
- Raw fruits and vegetables. Raw, unpeeled fruits and vegetables are a frequent source of cholera infection in areas where cholera is endemic. In developing nations, uncomposted manure fertilizers or irrigation water containing raw sewage can contaminate produce in the field.
- Grains. In regions where cholera is widespread, grains such as rice and millet that are contaminated after cooking and allowed to remain at room temperature for several hours become a medium for the growth of cholera bacteria.
Everyone is susceptible to cholera, with the exception of infants who derive immunity from nursing mothers who have previously had cholera. Still, certain factors can make you more vulnerable to the disease or more likely to experience severe signs and symptoms. Risk factors for cholera include:
- Poor sanitary conditions. Cholera is more likely to flourish in situations where a sanitary environment — including a safe water supply — is difficult to maintain. Such conditions are common to refugee camps, impoverished countries, and areas devastated by famine, war or natural disasters.
- Reduced or nonexistent stomach acid (hypochlorhydria or achlorhydria). Cholera bacteria can't survive in an acidic environment, and ordinary stomach acid often serves as a first-line defense against infection. But people with low levels of stomach acid — such as children, older adults, and people who take antacids, H-2 blockers or proton pump inhibitors — lack this protection, so they're at greater risk of cholera.
- Household exposure. You're at significantly increased risk of cholera if you live with someone who has the disease.
- Type O blood. For reasons that aren't entirely clear, people with type O blood are twice as likely to develop cholera as are people with other blood types.
- Raw or undercooked shellfish. Although large-scale cholera outbreaks no longer occur in industrialized nations, eating shellfish from waters known to harbor the bacteria greatly increases your risk.
Cholera can quickly become fatal. In the most severe cases, the rapid loss of large amounts of fluids and electrolytes can lead to death within two to three hours. In less extreme situations, people who don't receive treatment may die of dehydration and shock hours to days after cholera symptoms first appear.
Although shock and severe dehydration are the most devastating complications of cholera, other problems can occur, such as:
- Low blood sugar (hypoglycemia). Dangerously low levels of blood sugar (glucose) — the body's main energy source — may occur when people become too ill to eat. Children are at greatest risk of this complication, which can cause seizures, unconsciousness and even death.
- Low potassium levels (hypokalemia). People with cholera lose large quantities of minerals, including potassium, in their stools. Very low potassium levels interfere with heart and nerve function and are life-threatening.
- Kidney (renal) failure. When the kidneys lose their filtering ability, excess amounts of fluids, some electrolytes and wastes build up in your body — a potentially life-threatening condition. In people with cholera, kidney failure often accompanies shock.
Cholera is rare in the United States with the few cases related to travel outside the U.S. or to contaminated and improperly cooked seafood from the Gulf Coast waters.
If you're traveling to cholera-endemic areas, your risk of contracting the disease is extremely low if you follow these precautions:
- Wash hands with soap and water frequently, especially after using the toilet and before handling food. Rub soapy, wet hands together for at least 15 seconds before rinsing. If soap and water aren't available, use an alcohol-based hand sanitizer.
- Drink only safe water, including bottled water or water you've boiled or disinfected yourself. Use bottled water even to brush your teeth. Hot beverages are generally safe, as are canned or bottled drinks, but wipe the outside before you open them.
- Eat food that's completely cooked and hot and avoid street vendor food, if possible. If you do buy a meal from a street vendor, make sure it's cooked in your presence and served hot.
- Avoid sushi, as well as raw or improperly cooked fish and seafood of any kind.
- Stick to fruits and vegetables that you can peel yourself, such as bananas, oranges and avocados. Stay away from salads and fruits that can't be peeled, such as grapes and berries.
- Be wary of dairy foods, including ice cream, which is often contaminated, and unpasteurized milk.
Because travelers have a low risk of contracting cholera and because the traditional injected vaccine offers minimal protection, no cholera vaccine is currently available in the United States.
A few countries offer two oral vaccines that may provide longer and better immunity than the older versions did. If you'd like more information about these vaccines, contact your doctor or local office of public health. Keep in mind that no country requires immunization against cholera as a condition for entry.