During the present cholera pandemic the El Tor biotype of Vibrio cholerae has completely displaced the classic biotype, except in Bangladesh. We studied the distribution of these two biotypes in twenty-four rural districts during epidemics in 1988-89; there was clustering of the classic biotype in the southern region and of the El Tor biotype in all other regions. These findings suggest that the southern coastal region is now (and may always have been) the habitat of classic cholera. The selective distribution of V cholerae O1 biotypes in Bangladesh may have been affected by ecological changes occurring in the country.
PIP: Researchers from the International Center for Diarrheal Disease Research, Bangladesh in Dhaka took rectal swabs from 2386 patients with suspected cholera between September 1988-October 1989. They identified V. cholerae 01 in 951 (40%) cases and it was the most common enteric pathogen in the study. 71% of these were the Inaba serotype. El Tor biotype predominated (81% of the cases) with the Inaba serotype accounting for 86% of these cases. Classic cholera made up the remaining cases (18%) with the Ogawa serotype accounting for 98%. The difference in serotypes between classic cholera and the El Tor biotype was significant (p.001). 1984-1987 data revealed that the Ogawa serotype made up 96% and 83% of the classic and El Tor biotypes respectively. In the 7 southern districts of Bangladesh, classic cholera predominated (79%). On the other hand, almost all cases (99%) were El Tor biotype in the 17 northern and middle belt districts. A highly significant difference in distribution of the 2 isolates occurred (p.001). Even when the researchers included 1984-1987 data, the distribution pattern remained the same. Almost all classic biotypes in the southern region were resistant to tetracycline and the El Tor biotypes were sensitive to it. Previous reports claimed that the classic biotype disappeared from Bangladesh between 1973-1979, yet they only included data from the Matlab and Dhaka treatment centers. in 1982, researchers included samples from the south and found classic cholera. This study suggests that it had always been in the south. The researchers hypothesized that the coexistence of the 2 V. cholerae biotypes may be due to ecological changes including flooding, soil erosion, and construction of barrages and dams especially in the northeastern and middle belt regions.