Cholera

What Is Cholera? What Causes Cholera?

Worldwide, cholera affects 3-5 million people and causes 100,000-130,000 deaths a year as of 2010. Due to severe dehydration, fatality rates are high when untreated, especially among children and infants. Death can occur in otherwise healthy adults within hours. Those who recover usually have long-term immunity against re-infection.

The cholera epidemic in parts of Africa has been ongoing for more than 30 years, due to inadequate sanitation and water treatment systems.

Cholera was one of the earliest infections to be studied by epidemiological methods. Individuals' susceptibility to cholera is affected by their blood type, with those with type O blood being the most susceptible.

According to Medilexicon's medical dictionary:

Cholera is an acute epidemic infectious disease caused by the bacterium Vibrio cholerae. A soluble toxin elaborated in the intestinal tract by the bacterium activates the adenylate cylase of the mucosa, causing active secretion of an isotonic fluid resulting in profuse watery diarrhea, extreme loss of fluid and electrolytes, and dehydration and collapse, but no gross morphologic change in the intestinal mucosa.

Cholera was discovered in 1883 to be due to infection with Vibrio cholerae, a comma-shaped bacteria. The discovery was made by the great German bacteriologist Robert Koch (1843-1910). As head of a commission investigating the disease, Koch went to Egypt where an epidemic was taking place and there he found some sort of bacterium in the intestines of those dead of cholera but could neither isolate the organism nor infect animals with it.

Later in 1883 Koch went to India, where he wrote that he succeeded in isolating "a little bent bacilli, like a comma." He discovered that the bacteria thrived in damp dirty linen and moist earth and in the stools of patients with the disease.

Vibrio cholerae bacteria naturally live as rod-shaped bacteria existing primarily in plankton populations in shallow, brackish water. Attaching themselves to microscopic crustaceans called copepods that exist as part of the planktonic ecosystem, they move naturally through several environments. Colonies of the bacteria can exist on the surface of the copepods, flourishing during times when temperature, low salinity and high nutrient levels cause algal blooms in the estuary, explaining why cholera has traditionally been associated with monsoon conditions.

The bacteria also, however, exist as colonies of biofilms coating the surface of various natural features of the estuary, covering the water surface but also plants, stones, shells and similar items. They can take non-active form and survive in the silt of the estuary.

Finally the bacteria has been found resident in the egg masses of native midges, which serve as a reservoir for cholera bacteria. In all of these instances the bacteria is a natural inhabitant, not associated with damage to the ecology or the organisms with which it comes in contact.

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