(also called '''Asiatic cholera''') is a
Water-borne Disease caused by the
Bacterium ''
Vibrio Cholerae '', which are typically ingested by drinking
Contaminated Water , or by eating improperly cooked fish, especially
Shellfish . It was first described in a scientific manner by the
Portuguese physician
Garcia De Orta in the
16th Century .
Cholera produces potentially lethal secretory diarrhea through a pathway that involves the
Cystic Fibrosis Transmembrane Conductance Regulator , CFTR.
1 }} This discovery led to the hypothesis that carriers for
Cystic Fibrosis , who have lower levels of functional CFTR, are protected from the severe effects of cholera because they don't lose water as quickly as other people. This might explain the high incidence of cystic fibrosis among populations which were formerly exposed to cholera. However, no evidence of resistance ''
In Vivo '' has been observed in humans, and studies in mice have produced conflicting results.
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Recent
Genetic Research has determined that a person's susceptibility to cholera (and other diarrheas) is affected by their
Blood Type . Those with type O blood are the most susceptible. Those with type AB are the most resistant, virtually immune. Between these two extremes are the A and B blood types, with type A being more resistant than type B.
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About one million ''V. cholerae'' bacteria must be ingested to cause cholera in normally healthy adults, although increased susceptibility may be observed in those with a weakened
Immune System , individuals with decreased gastric acidity (as from the use of
Antacid s), or those who are
Malnourished .
Cholera is transmitted through ingestion of feces contaminated with the bacterium. The contamination usually occurs when untreated sewage is released into waterways, affecting the water supply, any foods washed in the water, and shellfish living in the affected waterway—it is rarely spread directly from person to person.
The resulting diarrhea allows bacteria to spread to other people under unsanitary conditions.
Symptoms include those of general GI tract upset: , muscle cramps, weakness, loss of tissue
Turgor , sunken eyes and wrinkled skin, severe
Metabolic Acidosis with
Potassium Depletion ,
Anuria , circulatory collapse and
Cyanosis . Death is through circulatory
Volume Shock (massive loss of fluid and electrolytes), and can occur within hours.
The root causes of these symptoms are the
Enterotoxin s that ''V. cholerae'' produces. The main enterotoxin, known as , interacts with
G Protein s and
Cyclic AMP in the intestinal lining to open
Ion Channels . As ions flow into the intestinal
Lumen , water follows through osmosis.
Cholera was originally
Endemic to the Indian subcontinent, with the
Ganges River likely serving as a contamination reservoir. It spread by trade routes (land and sea) to
Russia , then to
Western Europe , and from Europe to
North America . It is now no longer considered an issue in Europe and North America, due to
Filtering and
Chlorination of the water supply.
- 1816-1826 - : Previously restricted, the pandemic began in Bengal , then spread across India by 1820. It extended as far as China and the Caspian Sea before receding.
- 1829-1851 - reached Europe, ), Quebec , Ontario and New York in the same year, and the Pacific coast of North America by 1834.
- 1849 - Second outbreak in Paris. An outbreak in North America took the life of U.S. President James K. Polk
- 1852-1860 - mainly affected Russia, with over a million deaths.
- 1863-1875 - spread mostly in Europe and Africa .
- 1866 - Outbreak in North America.
- 1899-1923 - had little effect in Europe because of advances in public health, but Russia was badly affected again.
- 1961-1970s - began in Indonesia , called El Tor after the strain, and reached Bangladesh in 1963, India in 1964, and the USSR in 1966. From North Africa it spread into Italy by 1973. In the late 1970s there were small outbreaks in Japan and in the South Pacific.
- January 1991 to September 1994 - Outbreak in South America , apparently initiated by discharged ballast water. Beginning in Peru there were 1.04 million identified cases and almost 10,000 deaths. The causative agent was a non-O1, Nonagglutinable Vibrio (NAG) named O139 Bengal. It was first identified in Tamilnadu , India and for a while displaced El Tor in southern Asia before decreasing in prevalence from 1995 to around 10% of all cases. It is considered to be an intermediate between El Tor and the classic strain and occurs in a new serogroup. There is evidence as to the emergence of wide-spectrum resistance to drugs such as Trimethoprim , Sulfamethoxazole and Streptomycin .
The scientists with major contributions to fighting cholera were
John Snow , who found the link between cholera and drinking water in
1854 , and
Robert Koch , who identified ''V. cholerae'' as the bacillus causing the disease. The bacterium was originally isolated thirty years earlier by Italian anatomist
Filippo Pacini , but his results were not widely known around the world.
In the past, people travelling in ships would hang a yellow flag if one of the crews suffered from cholera. Boats with a yellow flag hung would not be allowed to disembark at any harbor. (See ''
Love In The Time Of Cholera '')
Treatment typically consists of aggressive
Rehydration and
Replacement Of Electrolytes , since the death rate is generally high due to the serious dehydration caused by the illness.
Tetracycline Antibiotics may have a role in reducing the duration and severity of cholera, although drug-resistance is occurring,
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and their effects on overall mortality is questioned.
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Although cholera can be life-threatening, it is easily prevented. In the United States and Western Europe, because of advanced water and sanitation systems, cholera is not a major threat. The last major outbreak of cholera in the United States was in
1911 . However, everyone, especially travellers, should be aware of how the disease is transmitted and what can be done to prevent it.
Simple sanitation is usually sufficient to stop an epidemic. There are several points along the transmission path at which the spread may be halted:
- Sickbed: Proper disposal and treatment of waste produced by cholera victims.
- Sewage: Treatment of general sewage before it enters the waterways.
- Sources: Warnings about cholera contamination posted around contaminated water sources.
- Sterilization: Boiling, filtering, and chlorination of water before use.
Filtration and boiling is by far the most effective means of halting transmission.
Cloth Filter s, though very basic, have greatly reduced the occurrence of cholera when used in poor villages in Bangladesh that rely on untreated surface water.
In general, education and sanitation are the limiting factors in prevention of cholera epidemics.
- Cholera facts from the United States FDA website: http://vm.cfsan.fda.gov/~MOW/chap7.html
- Cholera in 19th century,London: John Snow: website: http://www.ph.ucla.edu/epi/snow.html
- FDA "Bad Bug Book" entry: http://vm.cfsan.fda.gov/~MOW/chap7.html
- Cholera and the Cholera Toxin , by Elizabeth Cronenwett
