Vibrio cholerae
Cholera is a waterborne disease. It is an acute, diarrheal illness caused by infection of the intestine with a comma-shaped motile bacterium called Vibrio cholerae.
V.cholerae produces cholera toxin which acts on the mucosal epithelium is responsible for the characteristic diarrhea of the disease. Cholera toxins cause inflammation of the gut and production of a severe diarrahel. The watery diarrhea is speckled with flakes of mucus and epithelial cells (rice-water stool) and contains enormous numbers of vibrios.
Antigen of cholera plays an important role to spread the disease. The variation of antigens may result in epidemic and virulence. The flagellar of V. cholerae are shared with many water vibrios so they are not used to distinguish the strains causing epidemic. However, they do distinguish strains of V.cholerae into 139 known serotypes. Almost all of these strains of V.cholera are nonvirulent but the strains O1 and O139(Bengal) has been responsible for epidemic cholera. There are three distinct
O1 biotypes, named Ogawa, Inaba and Hikojima, and each biotype may display the classic or El Tor phenotype where to produce the major of eidemic of cholera disease.
V.cholerae O139 is a new serological strain with a unique O-antigen which partly explains the lack of residual immunity.
When people take the food that is contaminated with the cholera bacterium, most of them will suffer from the cholera disease. If bacteria are able to survive the gastric secretions and low pH of the stomach, they are well adapted to survival in the small intestine. V.cholerae
is resistance to bile salts and can penetrate the mucus layer of the small intestine, possibly helped by secretion of neuraminidase and proteases. They withstand the movement of gut by their own swimming ability and chemotaxis directed against the gut mucosa. The attachment of intestinal mucosa is probably by long filamentous fimbriae that form bundles at the poles of the cells. V.cholerae

produces a protease called mucinase that might contribute to detachment where vibrios would need to detach from cells that are being sloughed off of the mucosa in order to reattach to newly formed mucosal cells.
However, the infection is often mild or without symptoms. It can be severe when
Vibrio cholerae multiples in the intestine, releasing the powerful cholera toxin. The toxin activates the adenylate cyclase enzyme in cells of the intestinal mucosa leading to increased levels of intracellular cAMP, and secretion of H2O, Na ﹢ , K+, Cl ¯ and
HCO3 ¯ into the lumen of the small intestine. The effect is dependent on a specific receptor, monosialosyl ganglioside (GMI ganglioside) present on the surface of intestinal mucosal cells. The net effect of the toxin is to cause cAMP to be produce at an abnormally high rate which stimulates mucosal cells to pump large amounts of Cl ¯ into the intestinal contents. H2O, Na+ and other electrolytes follow due to the osmotic and electrical gradients caused by the loss of Cl ¯ . The lost H2O and electrolytes in mucosal cells are replaced from the blood. The loss of potassium ions may result in cardiac complications and circulatory failure. Thus, the toxin-damaged cells become pumps for water and electrolytes causing the diarrhea, loss of electrolytes and dehydration.
The main source of infection is water contamination by faeces from an infected person. The disease can spread rapidly in areas with inadequate treatment of sewage and drinking water. The cholera may also live in the environment in brackish rivers and coastal waters.
A person may get cholera by drinking water or eating food contaminated with the cholera bacterium. Sometimes, he can get the disease by handling of contaminated objects. Some people do not develop the typical symptoms of cholera although they are infected with vibrios. They are called carriers. The faeces from the carriers also contain vibrios with is a considerable threat as the carriers are free moving in a society.
The infection is often mild or without symptoms, but sometimes it can be severe.
The signs of severe diseases including profuse water diarrhaea with characteristic rice water stools, abdominal cramps, nausea, vomiting, dehydration and shock. Rapid loss of body fluid leads to dehydration and loss of mineral salts can cause death. Onset of the illness is generally sudden, with incubation periods varying from 6 hours to 5 days.
A healthy person may become hypotensive within an hour of the onset of symptoms and may die within 2-3 hours if no treatment is provided.

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Drink only water that have been boiled or treated with chlorine or iodine.
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Eat only food that has been thoroughly cooked.
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Proper sewage treatment
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Improvements in basic human hygiene (such as washing hands after defaecation)
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Isolation of patients and hygienic disposal of faeces and vomit from patients.
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Vaccination is recommended for people visiting areas where cholera is endemic and for those people living in such areas. The cholera vaccine contains heat-killed bacteria. It is only about 40-80% effective and protection only lasts for about 3-6 months.
Cholera SMART (Sensitive Membrane Antigen Rapid Test) is a rapid colorimetric immunoassay designed for the direct presumptive of Vibrio cholerae O1 in human feces as an adjunct to culture method for the diagnosis of cholera in symptomatic patients when cholera is endemic or epidemic.
ELISA Test (enzyme-linked immunosorbent assay) is another test for Vibrio cholerae found in the tested simple. First of all, take a plate that has tiny cups cut into it –a 96-well plate. Then coat the inside of well with a specific antibody which is specific for cholera toxin. The sample is added. The cholera-toxin-specific antibodies will bind antigen of cholera toxin. The things don’t bind to the toxin will be washed away. A second antibody specific for the same antigen of cholera toxin is added where it bends to the antigen making a sandwach which is radioactive. Free antibody is washed away again and only the antibody-antigen sandwiches remain by measuring the radioactivity can show how much cholera toxin was present in the tested sample.
Cholera can be simply and successfully treated by immediate replacement of the fluid and salts lost through diarrhea. Patients can be treated with oral rehydration solution, by packing of water containing balanced salts (NaCl, NaHCO3, KCl) and sugar (glucose). The replacement must be at lease 1.5 volumes to each volume of stool lost within 4-6 hours. When the patients are shock, an intravenous fluid is required for replace the body fluid. The types of solution are Decca solution, Ringer’s solution and WHO diarrhea treatment solution.
Antibiotics, such as tetracyclines and chloramphenicol, are effective at destroying the vibrios and decreasing the diarrhoea. Tetracycline is the common antibiotic to shorten the course and diminish the severity of the illness.
Chlormphenicol is effective against tetracycline-resistance vibrios.

From the map, we can find that the cholera cases is occurred in many parts of the world, such as Peru, Brazil, U.S.A, Mexico, India, China and Russia. Comparing with the distribution map of cholera in 1997, the majority of cholera cases were occurred in the Africa.
Occurrence (1997)
Occurrence key: yellow = low, orange = medium, and red = high
Global mean AVHRR-derived NDVI image for 1987
Cholera distribution map derived from WHO Global Cholera Update 1997

The reason why cholera diseases are common in the Africa is due to the environmental pollution. The poor standard of public and personal hygiene is the main reason for getting the cholera. As the country is poor, people don’t care the surroundings where they live. There is a poor garbage and waste disposal. People live in such areas drink the untreated water from the river. The water is contaminated by a lot of pathogens included V.cholerae. Besides, people don’t concern with personal hygiene, so the places where they live are very dirty and awful. Thus, this increases the numbers of flies which act as vectors in transferring faecal material with
V.cholerae to food .
In addition, the weather is the factor related to transmit the diseases. As the average temperature is high in the Africa, it increases the number of vectors (files) by rapid reproduction. This increases the chance of transmitting the disease.
However, the residents in the areas with endemic cholera disease develop a certain antibodies against infection by certain type of V.cholerae. It is because they had been suffered from the diseases in such areas. They would get a less chance to get the endemic diseases. On the other hand, there is no residual immunity against other epidemic type of V.cholerae
in the indigenous population. Previous exposure to Vibrio cholerae O1 does not provide protective immunity against Vibrio cholerae O139.
The countries have advanced water and sanitation systems, cholera is not a major threat, however, everyone, especially travelers, should be aware of how the disease is transmitted as they would get the disease easily during the traveling and transmit the disease to the other people.
Cholera in Hong Kong ( in 1997 )
Cholera in Hong Kong
Notes: y-axis - number of notifications (in different scales) x-axis - month in calendar year solid line in red - monthly means of past 5 years (1992-1996)
- monthly notifications in 1997

The serious condition of cholera was in the June in 1997 whereas that of cholera is in 1992-1996 were in the August (1992-1996). As a result, the summer is the common season that people get the disease in Hong Kong due to the hot weather. The food is contaminated easily by V.cholerae
causes cholera.
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Improve the standard of public and personal hygiene
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Proper sewage treatment
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Control of the number of vectors, e.g. files
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Better waste disposal and water flashing
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Better methods of keeping food
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Do not drink the treated water and uncooked food, especially shellfish
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Isolation of patients and hygienic disposal of faeces and vomit from patients
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Better drugs and vaccine is provided for the poor country.