Cholera: Prevention is better than cure

Cholera is a diarrhoeal disease caused by the bacteria known as Vibrio cholerae. The infection leads to a form of diarrhoea in which the patient passes the so called rice-water stool instead of the usual formed faeces. The cause of such stools is now well understood. On entering the human intestine through contaminated food or water, the Vibrio cholerae lodges itself in small intestine. Here it secretes certain proteinaceous substances (known as enterotoxins), which attach to the specific receptors (Gm ganglioside)on the intestinal cell surface. A part of enterotoxin then enters the intestinal epithelial cells and activates the metabolic pathway in them leading to a profuse outpouring of fluids from them into the intestinal lumen. The bacteria themselves, however, do not invade the tissue. The disease had been endemic in India down the centuries, mainly in the Ganges and Brahmputra deltas in Bengal. The record of spread of Cholera throughout the world is available only after 1817 when the first pandemic occurred.  Since then six such pandemics are on record showing that the disease affected millions of people all over the world with high rate of mortality and morbidity. The seventh pandemic spread from the Sulwesi Island in Indonesia in 1961 that was caused by a biotype el Tor of Vibrio cholerae.

The man is the only source of the disease. The spread occurs through a contaminated environment. An infected patient excretes around 10⁷ to 10² bacteria per ml of stool which may further contaminate drinking water through sewage pollution. Wells and reservoirs of surface water (lakes and ponds) can get contaminated easily.  Food is another source of infection. All people in the endemic area should use boiled cooled water for drinking. Food handlers can also act as transmitters of infection. Flies act as mechanical transmitters of Cholera infection. Sanitation staff should be alerted to decontaminate the water-bodies with permitted chemicals.

The clinical picture may range from an asymptomatic carrier state to the fulminant disease. The most characteristic feature is rice-water stool and a precipitate vomiting. Dehydration may develop due to fluid loss and if not treated, the patient may collapse within 24 hours. Tentative diagnosis of disease can be made by the microscopic examination of stool, where a hanging drop preparation on a slide would show darting mobility of the bacteria. The specific diagnosis is made by growing the bacteria on artificial media in the laboratory and by serotyping of bacterial colonies grown on media.

The disease is treated by replacing the lost fluids and electrolytes, intravenously if the patient is admitted to a hospital or orally through oral rehydration powder. Tetracycline is the drug of choice. Sulphonamides, furazolidne and cotrimethoxazole have also been found to be useful. Drugs should never be taken without medical consultation. Cholera is one of the diseases which can be prevented by vaccination controlled by sanitation. The source of infection being man alone and the commonest vehicle of transmission is the water. Special attention should therefore be paid to the purity of water and the ice made from it for human consumption. The disposal of human excreta and garbage should be safe and soiled clothes of the patient must be disinfected. The isolation and treatment of Cholera patients is must. The outbreak of cholera should be notified at national level immediately for adequate prophylactic vaccination of people traveling to that area. The cholera vaccine (vaccine developed from attenuated Vibrio cholerae) is given by intramuscular injection provides effective protection for two to three months in around 89% of vaccinated population. However, oral vaccines of cholera are also available with variable protective efficacy.