Cholera: Causes, Symptom, Treatment & Prevention
Cholera is an acute infectious disease caused by a bacterium, Vibrio cholerae (V. cholerae), which results in a painless, watery diarrhea in humans. Some affected individuals have copious amounts of diarrhea and develop dehydration so severe it can lead to death. Most people who get the disease ingest the organisms through food or water sources contaminated with V. cholerae.
V. cholerae was first isolated as the cause of cholera by Filippo Pacini in 1854, but his discovery was not widely known until Robert Koch (who also discovered the cause of tuberculosis), working independently 30 years later, publicized the knowledge and the means of fighting the disease. The history of cholera repeats itself. The U.S. National Library of Medicine houses original documents about multiple cholera outbreaks in the U.S. from the 1820s to the 1900s, with the last large outbreak in 1910-1911. Since the 1800s, there have been seven cholera pandemics (worldwide outbreaks). Multiple outbreaks worldwide continues into the 21st century with outbreaks in India, Iran, Vietnam, and several African countries occurring over the last 10 years (most recent outbreaks occurred in Haiti and Nigeria in 2010-2011). Why is cholera history repeating itself? The answer can be traced back to Dr. Snow's studies that show a source (water or occasionally food) contaminated with V. cholerae can easily and rapidly transmit the cholera-causing bacteria to many people. Until safe water and food is available to all humans, it is likely that cholera outbreaks will continue to happen.
Cholera is caused by the bacterium V. cholerae. This bacterium is Gram stain-negative and has a flagellum (a long, tapering, projecting part) for motility and pili (hair like structures) used to attach to tissue. Although there are many V. cholerae serotypes that can produce cholera symptoms, the O groups O1 and O139, which also produce a toxin, cause the most severe symptoms of cholera. O groups consist of different lipopolysaccharides-protein structures on the surface of bacteria that are distinguished by immunological techniques. The toxin produced by these V. cholerae serotypes are an enterotoxin composed of two subunits, A and B; the genetic information for the synthesis of these subunits is encoded on plasmids (genetic elements separate from the bacterial chromosome). In addition, another plasmid type encodes for a pilaus (a hollow hairlike structure that can augment bacterial attachment to human cells and facilitate the movement of toxin from V. cholerae into human cells). The enterotoxin causes human cells to extract water and electrolytes from the body (mainly the upper gastrointestinal tract) and pump it into the intestinal lumen where the fluid and electrolytes are excreted as diarrheal fluid. The enterotoxin is similar to toxin formed by bacteria that cause diphtheria in that both bacterial type secret the toxins in their surrounding environment where the toxin then enters the human cells. The bacteria are usually transmitted by drinking contaminated water, but the bacteria can also be ingested in contaminated food, especially seafood such as raw oysters.
Vibrio cholerae, the bacterium that causes cholera, is usually found in food or water contaminated by feces from a person with the infection. Common sources include:
- Municipal water supplies
- Ice made from municipal water
- Foods and drinks sold by street vendors
- Vegetables grown with water containing human wastes
- Raw or undercooked fish and seafood caught in waters polluted with sewage
When a person consumes the contaminated food or water, the bacteria release a toxin in the intestines that produces severe diarrhea. It is not likely you will catch cholera just from casual contact with an infected person.
The symptoms and signs of cholera are a watery diarrhea that often contains flecks of whitish material (mucus and some epithelial cells) that are about the size of pieces of rice. The diarrhea is termed "rice-water stool" and smells "fishy." The volume of diarrhea can be enormous; high levels of diarrheal fluid such as 250 cc per kg or about 10 to 18 liters over 24 hours for a 70 kg adult can occur. People may go on to develop one or more of the following symptoms and signs:
- Rapid heart rate
- Loss of skin elasticity (washer woman hands sign; see figure 2)
- Dry mucous membranes
- Low blood pressure
- Muscle cramps
- Restlessness or irritability (especially in children)
Those infected require immediate hydration to prevent these symptoms from continuing because these signs and symptoms indicate that the person is becoming or is dehydrated and may go on to develop severe cholera. People with severe cholera (about 5%-10% of previously healthy people; higher if a population is compromised by poor nutrition or has a high percentage of very young or elderly people) can develop severe dehydration, leading to acute renal failure, severe electrolyte imbalances (especially potassium and sodium), and coma. If untreated, this severe dehydration can rapidly lead to shock and death. Severe dehydration can often occur four to eight hours after the first liquid stool, ending with death in about 18 hours to a few days in undertreated or untreated people. In epidemic outbreaks in underdeveloped countries where little or no treatment is available, the mortality (death) rate can be as high as 50%-60%.
Treatment & Prevention:
Although there is a vaccine against cholera, the CDC and World Health Organization don't normally recommend it because it may not protect up to half of the people who receive it and it lasts only a few months. However, you can protect yourself and your family by using only water that has been boiled, water that has been chemically disinfected, or bottled water. Be sure to use the bottled, boiled, or chemically disinfected water for the following purposes:
- Preparing food or drinks
- Making ice
- Brushing your teeth
- Washing your face and hands
- Washing dishes and utensils that you use to eat or prepare food
- Washing fruits and vegetables
To disinfect your own water, boil it for one minute or filter it and add two drops of bleach or one-half of an iodine tablet per liter of water.
You should also avoid raw foods, including the following:
- Unpeeled fruits and vegetables
- Unpasteurized milk and milk products
- Raw or undercooked meat or shellfish
- Fish caught in tropical reefs, which may be contaminated
If you develop severe, watery diarrhea and vomiting -- particularly after eating raw shellfish or traveling to a country where cholera is epidemic -- seek medical help immediately. Cholera is highly treatable, but because dehydration can happen quickly, it's important to get cholera treatment right away.
Hydration is the mainstay of treatment for cholera. Depending on how severe the diarrhea is, treatment will consist of oral or intravenous solutions to replace lost fluids. Antibiotics, which kill the bacteria, are not part of emergency treatment. They reduce the duration of diarrhea by half and also reduce the excretion of the bacteria, thus helping to prevent the spread of the disease.