What are the causes of cholera?

 Most people contract cholera through drinking water or eating food that has been faecally contaminated by the bacteria. Person to person transmission is rare.

Uncooked shellfish, cooked rice, fresh fruits and vegetables can become sources of the disease, but potable water remains the most important source.

On the whole, cholera is a disease that affects economically disadvantaged communities with poor sanitary conditions. In developed countries such as the USA, cholera has been very rare over the last 100 years. Less than 10 cases are reported in the USA each year, mostly in travellers to endemic areas.

Epidemics usually occur in areas where there is loss of sanitary human waste disposal, lack of safe drinking water, and limited access to healthcare facilities usually in areas of over-crowding, war or famine. But cholera can also spread after a natural disaster such as a flood or earthquake, when fresh water supplies are disrupted.

Endemic areas include India, Asia, sub-Saharan Africa, Mexico, South and Central America.

Vibrio choleraeis a human pathogen. Epidemics seem to follow a cyclical pattern. Periods of rain are essential for a resurgence of the disease. When environmental conditions are unfavourable, the bacteria survive in the water by attaching to algae or the shells of shellfish. After heavy rains, however, when you have large quantities of fresh water at the mouth of rivers, the levels of salinity change and the organisms begin to multiply and move upstream. Communities living close to the river get infected when they use water from the river which is contaminated by the cholera bacteria.

As bacteria infect the community's water supply, more and more people become infected, until there's nobody else for the bacteria to infect, or the community has built up immunity.

Most recently, outbreaks have occurred in Haiti and Nigeria. The most recent outbreak in South Africa occurred in 2008-2009, when the cholera outbreak from Zimbabwe spread to several provinces, predominately Limpopo and Mpumalanga provinces.

(Previously reviewed by Professor Willem Sturm, Head of the Medical Microbiology and Infectious Diseases department at the Nelson Mandela School of Medicine in Durban)
(Reviewed by Dr Miscka Moodley, Microbiologist, UCT, March 2011)

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