Cholera
Cholera (or Asiatic cholera or epidemic cholera) is a severe diarrheal disease caused by the bacterium Vibrio cholerae Transmission to humans is by ingesting contaminated water or food. The major reservoir for cholera was long assumed to be humans, but some evidence suggests that it is the aquatic environment.
V. cholerae is a Gram-negative bacteria which produces cholera toxin, an enterotoxin, whose action on the mucosal epithelium lining of the small intestine is responsible for the characteristic massive diarrhea of the disease In its most severe forms, cholera is one of the most rapidly fatal illnesses known: 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 More commonly, the disease progresses from the first liquid stool to shock in 4-12 hours, with death following in 18 hours to several days without rehydration treatment.
Prevention
Although cholera can be life-threatening, it is nearly always easily prevented, in principle, if proper sanitation practices are followed. In the United States and Western Europe, because of advanced water treatment and sanitation systems, cholera is no longer 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. Good sanitation practices, if instituted in time, 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 the germ infected fecal waste (and all clothing and bedding that come in contact with it) produced by cholera victims is of primary importance.
* Sewage: Treatment of general sewage before it enters the waterways or underground water supplies prevent possible undetected patients from spreading the disease.
* Sources: Warnings about cholera contamination posted around contaminated water sources with directions on how to decontaminate the water.
* Sterilization: Boiling, filtering, and chlorination of water kill the bacteria produced by cholera patients and prevent infections, when they do occur, from spreading. All materials (clothing, bedding, etc.) that come in contact with cholera patients should be sterilized in hot water using (if possible) chlorine bleach. Hands, etc. that touch cholera patients or their clothing etc. should be thoroughly cleaned and sterilized. All water used for drinking, washing or cooking should be sterilized by boiling or chlorination in any area where cholera may be present. Water filtration, chlorination and boiling are by far the most effective means of halting transmission. Cloth filters, 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, public health education and good sanitation practices are the limiting factors in preventing transmission.
Susceptibility
Recent epidemiologic research suggests that an individual's susceptibility to cholera (and other diarrheal infections) is affected by their blood type: Those with type O blood are the most susceptible[11] while those with type AB are the most resistant. Between these two extremes are the A and B blood types, with type A being more resistant than type B
About one million V. cholerae bacteria must typically 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 antacids), or those who are malnourished.
It has also been hypothesized that the cystic fibrosis genetic mutation has been maintained in humans due to a selective advantage: heterozygous carriers of the mutation (who are thus not affected by cystic fibrosis) are more resistant to V. cholerae infections In this model, the genetic deficiency in the cystic fibrosis transmembrane conductance regulator channel proteins interferes with bacteria binding to the gastrointestinal epithelium, thus reducing the effects of an infection.
Transmission
Drawing of Death bringing the cholera, in Le Petit Journal.
Drawing of Death bringing the cholera, in Le Petit Journal.
Persons infected with cholera have massive diarrhea. This highly liquid diarrhea, which is often compared to "rice water", is loaded with bacteria that can spread under unsanitary conditions to infect water used by other people. Cholera is transmitted from person to person through ingestion of feces contaminated water loaded with the cholera bacterium. The source of the contamination is typically other cholera patients when their untreated diarrhea discharge is allowed to get into waterways or into groundwater or drinking water supply. Any infected water and any foods washed in the water, and shellfish living in the affected waterway can cause an infection. Cholera is rarely spread directly from person to person. V. cholerae occurs naturally in the plankton of fresh, brackish, and salt water, attached primarily to copepods in the zooplankton. Both toxic and non-toxic strains exist. Non-toxic strains can acquire toxicity through a lysogenic bacteriophage Coastal cholera outbreaks typically follow zooplankton blooms. This makes cholera a zoonosis.