Cholera is an acute gastrointestinal disease caused by the Gram-negative bacterium Vibrio cholerae. It is transmitted primarily via the fecal-oral route through the ingestion of contaminated water or food.
Vibrio cholerae is a motile, Gram-negative bacterium of the family Vibrionaceae, primarily associated with waterborne outbreaks in areas with inadequate sanitation. Although over 200 serogroups of V. cholerae exist, only O1 and O139 are responsible for epidemic cholera. The O1 serogroup, particularly the El Tor biotype, has been implicated in several global pandemics since the 1960s. In 1992, the emergence of O139 in South Asia marked a notable shift in the epidemiology of cholera. These strains produce cholera toxin and are capable of sustained transmission in human populations.
Large outbreaks often occur in settings of overcrowding, natural disasters, or displacement, where fecal contamination of drinking water is prevalent. The disease burden is highest in regions with poor infrastructure and limited access to medical care. The infectious dose of V. cholerae is high due to the bacterium's vulnerability to acidic gastric conditions. However, when stomach acidity is reduced—due to medications, surgery, or co-ingested food—lower inocula can initiate infection.
The clinical presentation of cholera is marked by painless, voluminous diarrhea without blood or leukocytes. In severe cases, fluid losses can exceed 20 liters per day, rapidly leading to hypovolemic shock. Cholera is a potentially life-threatening disease and can be fatal without medical intervention, particularly in young children, older adults, and individuals with underlying health conditions. Mortality in untreated individuals can reach 50%, but with the timely administration of oral or intravenous rehydration therapy, outcomes improve significantly. The disease typically follows a self-limiting course of 5 to 7 days. In endemic regions, rapid diagnosis and access to rehydration therapy are essential to minimize fatality during outbreaks.
Cholera is a gastrointestinal disease caused by Vibrio cholerae, which spreads through the consumption of contaminated water or food.
In the small intestine, the bacterium adheres to the epithelial cells.
The bacterium then releases cholera toxin, composed of one A subunit and five B subunits.
The B subunits bind to GM1 ganglioside receptors on the epithelial cell, allowing the toxin to enter the host cell by endocytosis.
Inside the cell, the A subunit is cleaved into A1 and A2 fragments.
The A1 fragment uses nicotinamide adenine dinucleotide as a donor to ADP-ribosylate the Gs protein, locking it in an active state.
As a result, adenylate cyclase becomes overstimulated and continuously converts ATP into cyclic AMP.
Elevated cyclic AMP levels open ion channels, causing anions like chloride and bicarbonate ions to rush into the intestinal lumen.
An osmotic gradient is created that draws water out of the cells.
The outcome is profuse watery diarrhea, which causes dehydration and electrolyte imbalance.
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