Cholera is a bacterial disease usually spread through contaminated water. Cholera causes severe diarrhea and dehydration. Left untreated, cholera can be fatal in a matter of hours. Cholera is easily treated. Every year, there are an estimated 3–5 million cholera cases and 100 000–120 000 deaths due to cholera. The short incubation period of two hours to five days, enhances the potentially explosive pattern of outbreaks. During the 19th century, cholera spread across the world from its original reservoir in the Ganges delta in India. Six subsequent pandemics killed millions of people across all continents. The current (seventh) pandemic started in South Asia in 1961, and reached Africa in 1971 and the Americas in 1991. Cholera is now endemic in many countries. Modern sewage and water treatment have virtually eliminated cholera in industrialized countries. The risk of cholera epidemic is highest when poverty, war or natural disasters force people to live in crowded conditions without adequate sanitation.

 Causes, Transmission and Symptoms
Cholera is an acute illness caused by infection of the intestine with the bacterium Vibrio cholerae. The infection is often mild or without symptoms, but sometimes it can be severe. Although cholera can be life-threatening, it is easily prevented and treated. Symptoms include: watery diarrhea, vomiting and leg cramps. A person may get cholera by drinking water or eating food contaminated with the cholera bacterium. In an epidemic, the source of the contamination is usually the feces of an infected person. The disease can spread rapidly in areas with inadequate treatment of sewage and drinking water. The cholera bacterium may also live in the environment in brackish rivers and coastal waters. The disease is not likely to spread directly from one person to another; therefore, casual contact with an infected person is not a risk for becoming ill.

Two serogroups of V. cholerae – O1 and O139 – cause outbreaks. V. cholerae O1 causes the majority of outbreaks, while O139 is confined to South-East Asia. Non-O1 and non-O139 V. cholerae can cause mild diarrhoea but do not generate epidemics.

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. 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.

For infection to develop, many bacteria must be consumed. Then, there may be too many for stomach acid to kill, and some bacteria can reach the small intestine, where they grow and produce a toxin. The toxin causes the small intestine to secrete enormous amounts of salt and water. The body loses this fluid as watery diarrhea. It is the loss of water and salt that causes death. The bacteria remain in the small intestine and do not invade tissues.

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. Seafood. Eating raw or undercooked seafood, especially shellfish, that originates from certain locations can expose you to 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. 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 and Disease Burden
Cholera transmission is closely linked to inadequate environmental management. Typical at-risk areas include peri-urban slums, where basic infrastructure is not available, as well as camps for internally displaced people or refugees, where minimum requirements of clean water and sanitation are not met.

The consequences of a disaster – such as disruption of water and sanitation systems, or the displacement of populations to inadequate and overcrowded camps – can increase the risk of cholera transmission should the bacteria be present or introduced. Epidemics have never arisen from dead bodies.
Cholera remains a global threat to public health and a key indicator of lack of social development. Recently, the re-emergence of cholera has been noted in parallel with the ever-increasing size of vulnerable populations living in unsanitary conditions. The true burden of the disease is estimated to be 3–5 million cases and 100 000–120 000 deaths annually.

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: 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.  Household exposure: One at significantly increased risk of cholera if one lives with someone who has the disease. Compromised immunity: If one’s immune system is compromised for any reason, one is more susceptible to cholera infection.

 Complications
Approximately one in 20 infected persons has severe disease characterized by profuse watery diarrhea, vomiting, and leg cramps. In these persons, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours. If dehydration is not treated, loss of water and salts can lead to kidney failure, shock, coma, and death. In people who survive, symptoms usually subside in 3 to 6 days. Most people are free of the bacteria in 2 weeks. The bacteria remain in a few people indefinitely without causing symptoms. Such people are called carriers.

Although shock and severe dehydration are the most devastating complications of cholera, other problems can occur, such as: Low blood sugar (hypoglycemia),  Low potassium levels (hypokalemia), 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

Seeking Medical Advice
Seek immediate medical care if you develop severe diarrhea or vomiting and are in or have very recently returned from a place where cholera occurs. If you believe you may have been exposed to cholera, but your symptoms are not severe, call your doctor. Be sure to tell him or her that you suspect your illness may be cholera. If your doctor determines that you don't need to come in immediately, take measures to avoid dehydration. Severe dehydration is the most dangerous potential complication of cholera. For diarrhea and vomiting that may be cholera-related, drinks such as water, juice and soda won't adequately replenish both fluids and electrolytes. Instead, use an oral rehydration solution. You can buy powdered packets of Oral Rehydration Salts (ORS), originally developed by the World Health Organization to treat diarrhea and dehydration in infants with cholera. Reconstitute the powder in water according to the directions on the package. Always purify the water first by boiling, filtration or other proven methods. Re-measure the water, then add the powdered oral rehydration material. If a pre-formulated solution is unavailable, you can make your own oral rehydration solution by mixing 1/2 teaspoon salt, 1/2 teaspoon baking soda, 3 tablespoons sugar and 1 liter (about 1 quart) of safe drinking water. Be sure to measure accurately because incorrect amounts can make the solution less effective or even harmful.

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. 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.

Treatment and drugs: Cholera requires immediate treatment because the disease can cause death within hours. Rehydration. The goal is to replace fluids and electrolytes lost through diarrhea using a simple rehydration solution, Oral Rehydration Salts (ORS), that contains specific proportions of water, salts and sugar. Intravenous fluids. During a cholera epidemic, most people can be helped by oral rehydration alone, but severely dehydrated people may also need intravenous fluids. Antibiotics. 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. Zinc supplements. Research has shown that zinc may decrease and shorten the duration of diarrhea in children.

 Outbreak response: Once an outbreak is detected, the usual intervention strategy is to reduce deaths by ensuring prompt access to treatment, and to control the spread of the disease by providing safe water, proper sanitation and health education for improved hygiene and safe food handling practices by the community. The provision of safe water and sanitation is a formidable challenge but remains the critical factor in reducing the impact of cholera. Rapid replacement of lost body water and salts is lifesaving. Most people can be treated effectively with a solution given by mouth. These solutions are designed to replace the fluids the body has lost. For severely dehydrated people who cannot drink, a salt solution is given intravenously. Solid foods can be eaten after vomiting stops and appetite returns. People are usually given an antibiotic to reduce the severity of diarrhea and make it stop sooner. Also, people who take an antibiotic are slightly less likely to spread the infection during an outbreak. Tetracycline or doxycycline is effective in adults, unless the bacteria in the area are resistant to tetracycline. Then, ciprofloxacin can be used.

Prevention: 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. Coffee, tea and other hot beverages, as well as bottled or canned soft drinks are generally safe. Eat food that's completely cooked and 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. 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.  A few countries offer two oral vaccines that may provide longer and better immunity than the older versions did. Purification of water supplies and appropriate disposal of human waste are essential. Other precautions include using boiled or chlorinated water and avoiding uncooked vegetables and undercooked fish or shellfish. A multidisciplinary approach based on prevention, preparedness and response, along with an efficient surveillance system, is key for mitigating cholera outbreaks, controlling cholera in endemic areas and reducing deaths.

(Dr. Syed Amin Tabish (FRCP, FACP, FAMS, MD) is Medical Superintendent at SKIMS, Srinagar)

Lastupdate on : Sun, 29 Aug 2010 21:30:00 Makkah time
Lastupdate on : Sun, 29 Aug 2010 18:30:00 GMT
Lastupdate on : Mon, 30 Aug 2010 00:00:00 IST