Severely dehydrated patients, who make up for five per cent of all clinical cases, require intravenous rehydration fluids. Cholera bacteria favour brackish water. Survival in seawater for more than 50 days has been demonstrated. The association of Vibrio cholerae with zooplankton has contributed to its global distribution. Under unfavourable conditions, the bacteria can survive in a dormant state, i.e. viable but not culturable.
Dormant bacteria contribute to the occurrence of seasonal epidemics.
Promising results in Vietnam In 1992, a killed oral cholera vaccine, manufactured locally in Vietnam and administered in two doses, has performed better. Protection for children aged from 1 to 5 years was similar to that of older persons. This outcome has been ascribed to the presence of certain colonisation antigens, toxins and haemagglutinins in the Vietnam vaccine that were not included in the vaccines used in Bangladesh. Capitalizing on the findings of the Bangladesh trial, further research has been conducted on the merits of using the cholera toxin's B subunit in oral vaccine formulations. It confers complete and early protection against cholera caused by either biotype.