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| CHOLERA |
Disease
Cholera is an acute diarrheal illness caused by certain serotypes of Vibriocholeriae. Infection is acquired by ingestion of contaminated food or water. The disease is toxin mediated and fever is unusual. The toxin acts on the intestinal epithelial cells of the small intestines, producing hyper secretion of water and chloride ion and thus leading to massive diarrhea upto 15 litres/day and may lead to profound hypovolumia.
Occurrence
Cholera occurs in epidemic under conditions of crowding, war and famine (e.g. refugee camps) and where sanitation is inadequate. Cholera is native to the Ganga delta in Indian subcontinent but its incidence of outbreaks has come down in last few decades due to better preventive measures. Now most of the cases are being reported from Africa and South East Asia mainly Bangladesh.
Risk for travellers
Travellers are not at significant risk from cholera provided that simple precautions are taken to avoid potentially contaminated food and water. Vaccination is of questionable benefit to general tourist travellers, for whom the risk is very low, and is therefore recommended only for individuals at increased risk of exposure, particularly emergency relief and health workers in refugee situations. Cholera vaccination is not required as a condition of entry to any country.
Vaccine
Two types of oral cholera vaccine have been developed. The first is killed whole cell (WC) vaccine. Two formulations of the killed WC vaccine have been prepared: one composed solely of killed bacteria while the other one also contains the non toxic. B supcervit of cholera toxin (WC/BS). Both the killed Cholera vaccines given orally, are safe and effective but WC/BS vaccine is proving better than WC vaccine. The inactivated or killed vaccine confers high-grade (85–90%) protection for 6 months after the second dose, to be given between 1-6 weeks after the first. After 3 years, protection remains as high as 62% in vaccine recipients over 5 years of age. In children between 2-6 years three doses of vaccines are given each separated by an interval of 1-6 weeks.
Oral cholera vaccine is licensed for resident of or travellers to endemic or epidemic areas. Immunisation should be completed at least 1 week before potential exposure. However, there is no requirement for cholera vaccination for international travel. Immunisation with cholera vaccine does not provide complete protection and all the residents of or travellers to a country where cholera exists should be warned that scrupulous attention to food, water, and personal hygiene is essential.
Live vaccine have been developed and is under field trails but none has been proved effective till date and thus are not recommended. Injectable cholera vaccine provides unreliable protection and is no longer recommended.
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