Cholera is caused by the bacterium Vibrio cholera, whose "natural reservoirs" are suggested to be "brackish rivers and coastal waters" . Human-volunteer feeding studies utilizing healthy individuals have demonstrated that approximately one million organisms need to be ingested to cause illness. After ingestion, the viable bacteria attach to the small intestine and produce cholera toxin . There are a number of causes which may contribute to the source, spread and severity of cholera. These include:
The consumption of food or water contaminated with the cholera bacterium. In particular, shellfish (oysters, ...) harvested from fecally polluted coastal waters are consumed raw have been a source of cholera. Vegetables and fruits which have been washed or rinsed with contaminated water may also transmit the infection in the bacterium is present.
Inadequate treatment of sewerage and drinking water. Poor standards of sanitation, leading to contaminated water supplies. Inadequate treatment of sewerage and drinking water may also result in an epidemic of cholera - in an epidemic, the source of contamination is usually the faeces of an infected person .
Conditions which may compromise or place a strain on hygiene, sanitation or other infrastructure (e.g. plumbing, water treatment systems etc.) may also led to an outbreak or epidemic of cholera. These conditions include famine, overpopulation, war and poverty.
Transmission of cholera through direct person-to-person contact is rare. Instead, cholera is predominantly spread through a number of alternate mediums:
Transmission by the faecal-oral route. Cholera is contracted almost exclusively by means of contaminated food and water. Water may be contaminated as its source, and may also transmit the bacterium through fruits and vegetables (as above) and also through cooking utensils, if they have been washed in contaminated water. "Moist grains, such as rice, millet or sorghum" are ideal vehicles...