Cholera

Cholera is an acute intestinal illness caused by the toxigenic bacterium Vibrio cholerae. While most infected individuals have no or mild to moderate symptoms, 5 percent have severe disease. Severe infection is characterized by large volumes of watery diarrhea and vomiting. Profuse amounts of diarrhea can lead to dehydration, metabolic disturbances, hypovolemic shock, and coma. Without appropriate fluid replacement, severe cholera can lead to death within hours. Without treatment, a cholera outbreak in a community may lead to fatality rates approaching 50 percent.

V. cholerae is a gram-negative, curved, motile bacillus. While humans are the only known hosts, V. cholerae can exist in aquatic environments. Infection is generally via contaminated water and less commonly food. Once ingested, the bacterium produces an enterotoxin that activates the adenylate cyclase enzyme on the mucosal epithelium of the intestine. Activation of the enzyme opens ion channels and allows ions to flow into the intestinal lumen. Subsequently, massive amounts of water may be osmotically drawn into the intestine leading to dehydration and circulatory shock.

Treatment for severe cholera consists of aggressive rehydration therapy to replace lost water and correct electrolyte imbalances. The World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) provide standardized sachets to be mixed with water to produce oral rehydration solution (ORS). ORS uses sodium-coupled glucose co-trans-port to stimulate resorption of salt and water. Therapy is given orally unless the patient is in shock or otherwise unable to take fluids by mouth, in which case they are given intravenously. In situations in which WHO/UNICEF ORS is not available, a rice- or cereal-based solution may be used. In severe cases, antimicrobial therapy may reduce the volume and duration of diarrhea and the period of vibrio excretion. There is no effective vaccine against cholera.

Originally endemic to the Indian subcontinent, there have been seven global cholera pandemics and multiple epidemics over the past 200 years. In 1854, in one of the most important events in the history of public health, John Snow removed the handle on the Broad Street water pump in London and proved that cholera was transmitted via contaminated water. Due to improved sanitation, cholera no longer poses a significant risk in the developed world. However, in 2004, the WHO reported over 100,000 cases of cholera causing over 2,300 deaths in a total of 56 countries and estimates that this represents only 5 to 10 percent of the true burden of disease.