Cholera

Definition

Cholera is a serious bacterial disease that often causes severe diarrhea. Cholera usually spreads through contaminated water. Left untreated, cholera can cause death in a matter of hours.

Modern sewage- and water-treatment facilities have virtually eliminated cholera in industrialized countries. The last major cholera outbreak in the United States occurred in 1911. But cholera is still present in other parts of the world, such as Asia, the Middle East, Latin America, and particularly India and sub-Saharan Africa. The risk of cholera epidemic is highest when poverty, war or natural disasters force people to live in crowded conditions without adequate sanitation, a common cause of cholera outbreaks.

Unlike many infectious diseases, cholera is easily treated. Death results from severe dehydration that can be prevented with a simple and inexpensive rehydration solution.

Symptoms

Most people exposed to the cholera bacterium 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. Most people who become sick with cholera experience only mild or moderate diarrhea that's often hard to distinguish from diarrhea caused by other problems.

Only about one in 10 infected people develops the typical signs and symptoms of cholera, which include:

• Severe, watery diarrhea. The incubation time for cholera is brief — usually one to five days after infection. Diarrhea comes on suddenly. Cholera diarrhea often is voluminous, flecked with mucus and dead cells, and has a pale, milky appearance that resembles water in which rice has been rinsed (rice-water stool). What makes cholera diarrhea so deadly is the loss of large amounts of fluids in a short time — as much as a quart an hour.
• Nausea and vomiting. Occurring in both the early and later stages of cholera, vomiting may persist for hours at a time.
• Muscle cramps. These result from the rapid loss of salts such as sodium, chloride and potassium.
• Dehydration. This can develop within hours after the onset of cholera symptoms — far more quickly than in other diarrheal diseases. Depending on how much 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, 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).
• Shock. Hypovolemic shock is one of the most serious complications of cholera dehydration. It occurs when low blood volume causes a drop in blood pressure and a corresponding reduction in the amount of oxygen reaching your tissues. 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 may also experience:

• Extreme drowsiness or even coma
• Fever
• Convulsions

Causes

Contaminated water supplies are the main source of cholera infection, although raw shellfish, uncooked fruits and vegetables, and other foods also can harbor cholera bacteria.

The bacterium that causes cholera, Vibrio cholerae, has 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. As many as 10,000 bacteria may adhere to a single crustacean. 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.

Most cholera outbreaks occur in spring and fall when ocean surface temperatures and algae blooms are at their height. More algae mean more copepods, and more copepods mean more cholera bacteria.

Cholera bacteria in people
When humans ingest cholera bacteria, they may not become sick themselves, but they still excrete the bacteria in their stool and can pass cholera disease to others through the fecal-oral route. This mainly occurs when human feces contaminate food or water supplies, both of which 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 include:

• 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. Cholera epidemics are most likely to occur in communities without adequate sanitation and in areas affected by natural disasters or war. People living in crowded refugee camps are especially at risk of cholera.
• Seafood. Eating raw or undercooked seafood, especially shellfish, that originate from certain locations can expose you to cholera bacteria. Most cases of cholera occurring in the United States since the 1970s have been traced to oysters and crab from the Gulf of Mexico and to seafood transported or smuggled from countries where cholera is endemic. Shellfish are a particular problem because they filter large amounts of water, concentrating the levels of cholera bacteria.
• 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. Fruits and vegetables may also become tainted with cholera bacteria during harvesting or processing.
• 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.

Bacteria produce strong toxin
Although V. cholerae is the source of cholera infection, 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).

Risk factors

Everyone is susceptible to cholera, with the exception of nursing infants who derive immunity from their mothers' milk. 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:

• Malnutrition. Malnutrition and cholera are interconnected. People who are malnourished are more likely to become infected with cholera, and cholera is more likely to flourish in places where malnutrition is common, such as 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 lack this protection, so they're more likely to develop cholera and to have severe signs and symptoms of the disease. Children and older adults, especially, tend to have lower than normal stomach acid levels. So do people who have had gastric surgery, who have untreated Helicobacter pylori infection, or who are taking antacids, H-2 blockers or proton pump inhibitors for ulcers. Antacids help neutralize stomach acid, and H-2 blockers and proton pump inhibitors reduce the amount of acid your stomach produces.
• Household exposure. You're more likely to develop cholera if you live with someone who has the disease. Up to half the household contacts of infected people also become sick.
• Compromised immunity. If your immune system is compromised for any reason, you're more susceptible to cholera infection.
• 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 raw shellfish — particularly oysters — from waters known to harbor the bacteria or shellfish transported by travelers from countries where cholera is endemic greatly increases your risk.

When to seek medical advice

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 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.

Tests and diagnosis

Although signs and symptoms of severe cholera may be unmistakable in endemic areas, the only way to confirm a diagnosis is to identify the bacteria in a stool sample. But because cholera requires immediate treatment and because all cases of watery diarrhea are treated in the same way, doctors are likely to begin rehydration before a definitive diagnosis is made.

They're also likely to carefully monitor vital signs such as blood pressure and pulse as well as blood sugar and electrolyte levels, and the amount of oxygen and carbon dioxide in the blood — all of which can be affected by the severely dehydrating effects of cholera.

Rapid cholera dipstick tests are now available, enabling health care providers in remote areas to confirm diagnosis of cholera earlier. Quicker confirmation helps to decrease death rates at the start of cholera outbreaks and leads to earlier public health interventions for outbreak control.

Complications

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 18 to 48 hours 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). A common cholera complication in children, this occurs when blood levels of glucose, the body's main energy source, fall abnormally low. Glucose is absorbed directly into your bloodstream after eating and enters your cells through the action of the hormone insulin. With severe cholera, people can become too ill to eat, so they don't get glucose from food and the body becomes unable to carry out normal glucose absorption. This may lead to unusually low blood sugar levels, 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. Hypokalemia is especially serious in people whose potassium stores have already been depleted by malnutrition.
• Kidney (renal) failure. When the kidneys lose their filtering ability, excess amounts of fluids and wastes build up in your body — a potentially life-threatening condition. In people with cholera, kidney failure often accompanies shock.

Treatments and drugs

The World Health Organization (WHO) has established guidelines for treating cholera. The goal is to replace fluids and electrolytes lost through diarrhea using a simple rehydration solution that contains specific proportions of water, salts and sugar. The solution, called Oral Rehydration Salts (ORS), is available as a powder that can be reconstituted in boiled or bottled water.

During a cholera epidemic, most people can be helped by oral rehydration alone, but severely dehydrated people may also need intravenous fluids. No matter which method is used, immediate treatment is critical because death from cholera can occur within hours. Without rehydration, approximately half the people with cholera die. With treatment, the number of fatalities drops to less than 1 percent.

In addition to rehydration, people who are severely ill with cholera may benefit from antibiotics, which can cut the length of the illness in half. Recent studies show that a single dose of azithromycin (Zithromax, Zmax) in adults or children with severe cholera helps shorten diarrhea duration and decreases vomiting.

Prevention

Cholera cases reported in the United States since 1995 have been traced to sources outside the U.S. or to contaminated and improperly cooked seafood from the Gulf Coast waters, and from Louisiana, where it was locally harvested after hurricanes Katrina and Rita, in October 2005.

If you're traveling to cholera-endemic areas, your risk of contracting the disease is extremely low if you follow these precautions:

• Wash your hands. Frequent hand washing is the best way to control cholera infection. Wash your hands thoroughly with hot, soapy water, especially before eating or preparing food, after using the toilet, and when you return from public places. Carry an alcohol-based hand sanitizer for times when water isn't available.
• Avoid untreated water. Contaminated drinking water is the most common source of cholera infection. For that reason, drink only bottled water or water you've boiled or disinfected yourself. Hot beverages such as coffee and tea as well as bottled or canned soft drinks, and wine and beer are generally safe. Carefully wipe the outside of all bottles and cans before you open them and ask for drinks without ice. Use bottled water to brush your teeth.
• Eat food that's completely cooked and hot. Choose food that's been thoroughly cooked and is served hot. Cholera bacteria can survive on room temperature food for up to five days and aren't destroyed by freezing. It's best to avoid street vendor food, but if you do buy it, make sure your meal is cooked in your presence and served hot.
• Avoid sushi. Don't eat raw or improperly cooked fish and seafood of any kind.
• Be careful with fruits and vegetables. When you're traveling, make sure that all fruits and vegetables that you eat are cooked or have thick skins that you peel yourself. Avoid lettuce in particular because it may have been rinsed in contaminated water.
• Be wary of dairy foods. Avoid ice cream, which is often contaminated, and unpasteurized milk.
• Cholera vaccine. 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.