Cholera
by Gary Cocke
Etiologic agent: Vibrio cholerae (1)
Transmission
Cholera is transmitted by the fecal oral route. The most common way that people become infected with cholera is by drinking water contaminated with the feces of a person with V. cholerae. Outbreaks often occur in areas with poor sewage and drinking water sanitization. V. cholerae also lives coastal waters and can attach to crustaceans called copepods. Copepods feed on algae and will follow their food source More algae means more copepods, which means more V cholerae in the water. Also, shellfish filter a lot of water which can concentrate bacterial cells in their body. These shellfish can cause infection in people when they are eaten, and this is the cause of most cases contracted in America when the shellfish originate from an endemic cholera area. In areas where cholera is endemic it can also be transmitted through raw fruits and vegetables, since the water and fertilizer used to grow the crops are often contaminated with V. cholerae. Because more than a million bacteria are needed to cause illness, cholera is not normally transmitted through casual person to person contact. (5)
Resevoirs
The natural reservoir for V. cholerae was thought for a long time to be humans, but evidence now supports that the reservoir is the aquatic environment. (3)
General characteristics of V. cholerae
V. cholerae is a gram-negative rod which has a single polar flagellum for motility. It is oxidase positive which distinguishes it from enterics, and can be oxidative or fermentative in their metablolism, which distinguishes it from pseudomonads.(3) The microorganism is the source of the cholera infection, but the effects of the disease are attributable to the very potent enterotoxin called cholera toxin or CTX. This toxin interferes with the normal flow of sodium and chloride in the intestinal wall causing the body to secrete huge amounts of water and electrolytes. This is the cause for the diarrhea that is associated with the illness.(5)
Key tests for identification
Because the signs and symptoms of severe cholera are unmistakable in endemic areas, the only way to confirm the diagnosis is to identify the bacteria in the stool sample. (5) Dipsticks are now available for rapid diagnosis. Since the areas which are endemic for cholera are usuallylera are unmistakable in endemic areas, the only way to confirm the diagnosis is to identify the bacteria in the stool sample. (5) Dipsticks are now available for rapid not located next to clinical laboratories, the test is easy to transport and requires little to no training to use. The test is based on the principle of immunochromatography, and all you do is immerse the dipstick into a stool sample and wait 2-15 minutes. If two red lines appear then the test is positive for V. cholerae. (2)
Signs and symptoms
Most people exposed to V. cholerae never become ill, but can still transmit the bacteria through their feces. Most people who become sick with cholera only experience mild diarrhea which is hard to distinguish from run of the mill diarrhea. About 10% of people infected with cholera experience the typical signs and symptoms associated with the disease. The main sign of cholera is severe watery diarrhea. The diarrhea is often a milky color and resembles water which rice has been rinsed with. The person may also experience nausea, muscle cramps, dehydration, and shock. The shock which people may experience is attributable to the dehydration, and it is the most serious affect. Shock can cause death within minutes. Children with cholera have the same symptoms as adults, but may also experience extreme drowsiness or coma, fever, and convulsions. (5)
Historical information
Descriptions of cholera date back to Hippocrates and Sanskrit writings. Epidemic cholera was described by Garcia del Huerto, a Portugese physician in India, in 1563. In 1849 John Snow proved water as a mode of transmission for cholera, and in 1883 Robert Koch isolated the cholera vibrio from the feces of patients, proving it as the causative agent. (3) Cholera was simply endemic in most of the world before sewage and water sanitization, and still is endemic in parts of the world without proper sanitization. The first long distance spread of cholera began in 1817 with the spread of cholera from Europe to the Americas. Since the first long-distance spread of cholera until the early twentieth century six waves of cholera devastated the world in epidemic fashion. In 1961 a more virulent strand of cholera called El Tor emerged which ravaged the Phillipines and was known as the seventh global pandemic. El Tor also emerged again in Peru in 1991 killing 9642 people and infecting 1,041,422. Cholera was prevalent in the 1800s in America, but has been virtually eliminated with modern sewage and water treatments the seventh global pandemic. El Tor. 90% of cases of cholera are due to traveling abroad, and most of the other cases are due to eating shellfish from endemic areas. (3)
Virulence factors
Cholera has two factors which contribute most greatly to its virulence. First is the protein TCP pili, which allows the microorganism to adhere to the mucosa in the intestines. The TCP pili also allows the microorganism to clump together. Another virulence factor is the CTX toxin, which is attributable to viral DNA being added to the bacteria. The viral DNA which gives the bacteria the toxin also tells the bacteria to multiply like crazy when the bacteria is in the intestines. (6)
Control/Treatment
The World Health Organization has established guidelines for the treatment of cholera, in which the goal is to replace lost body fluids by using Oral Rehydration Salts. The Oral Rehydration Salts contain a specific mixture of salts, sugars, and water, and are available in powder form. The powder is then mixed with water that has been boiled and given to the patient. (5)
Prevention
The best way to prevent contacting cholera is to wash you hands, avoid untreated water, avoid raw or undercooked food, be wary of fruits and vegetables in endemic areas, and be wary of dairy food in endemic areas. There is no vaccine for cholera available in America, because the traditional injected vaccines offered minimal protection against the disease. (5) In other countries there is an oral cholera vaccine (OCV) that has been proven safe and effective 85-90% after six months in all age groups, and drops to 62% after 1 year. It is administered in 2 doses 10 to 15 days apart and given with 150 mL of safe water. Since 2006 the WHO has carried out several immunization campaigns. (1)
Current outbreaks locally
The last outbreak of cholera in the United States occurred in 1911.(5) However there are sporadic cases of which 90% are attributable to travel and most of the other cases are due to seafood from endemic areas. (3) In America approximately 1 in 45,333,334 catch cholera, and there were 6 notified cases in 1999. (7)
< 90% are attributable to travel and most ofp class="MsoNormal">Current outbreaks globally
Cholera is endemic in much of Asia, the Middle East, Latin America, and particularly in India and Sub-Saharan Africa. (5) In 2005 there were 131,933 reported cases of cholera and 2272 deaths. 14 countries accounted for 58% of the reported cases and Africa reported 125,082 of the cases. (1)
References
1. World Health Organization. http://www.who.int/mediacentre/factsheets/fs107/en/index.html . accessed 5/5/08
2.
Pasteur Institute. Dipsticks For Rapid Diagnosis of Cholera. http://www.pasteus.fr/actu/presse/priss/03Cholera-E.htm . accessed 5/5/08
3. Todar�s Online Textbook of Bacteriology. Vibrio cholerae and Asiatic Cholerae. http://www.textbookofbacteriology.net/cholera.html . accessed 5/5/08
4. Center for Disease Control. 4.&nd/disease_listing/cholera_gi.html" style="color: blue; text-decoration: underline; text-underline: single"> http://www.cdc.gov/nczved/dfbmd/disease_listing/cholera_gi.html . accessed 5/5/08
5. Mayo Clinic http://www.mayoclinic.com/print/cholera/DS00579/METHOD=print&DSECTION=all . accessed 5/5/08
6. Harvard Medical School Office of Public Affairs. How the Cholera Bacterium Got Its Virulence. http://www.hms.harvard.edu/news/releases/696cholera.html . Accessed on 5/5/08