Probable role of blue-green algae in maintaining endemicity and seasonality of cholera in Bangladesh: a hypothesis.

Abstract

INTRODUCTION A good example of how reservoirs have gone undetected in Australia is shown by Rogers et al. (4). If Vibrio cholerae 01 has been isolated from aquatic there had not been an unusual drought, which resulted in environments in various parts of the world (1-14). the need for a supplementary water supply from a nearby However, little is known about its ecology, notably its river, the presence of V. cholerae 01 in Queensland rivers interaction with the resident flora in an aquatic ecosystem. would have gone unnoticed. It was by accident that the This gap in our knowledge is due to the fact that in the rivers were found to be reservoirs of V. cholerae 01. The past, investigations of the biology of V. cholerae have salinity of water in the rivers is low, in which V. cholerae been mainly based on the assumption that organisms 01 cannot survive long. Therefore, some sort of aquatic causing cholera occurred only clinically in man. flora in this water system must have been supporting the However, Colwell etal. (15) hypothesized that survival of V. cholerae 01. V. cholerae are autochthonous members of the bacterial Islam etal. (19) demonstrated the long-term survival flora of brackish water and estuarine systems. This and multiplication of V. cholerae 01 inside the hypothesis offered a new perspective on the ecology of mucilaginous sheath of a blue-green alga Anabaena this organism. variabilis. We are not aware of any other studies which , ,, j , , , , • , r have shown such a long survival of V. cholerae 01 in Marshall (16) suggested that the enhanced survival oi r, ,, .. . . . ° . . , fresh water m the laboratory. However, studies have microorganisms in aquatic environments is due to , , , , ,, , T/ ■ , . ? ., ^ r demonstrated that V. cholerae Ol survive better with association with some non-living and living surfaces ^ ,, , OA 6 ® aquatic flora (14,20-30). where they find the microenvironment favourable. Our study, the first attempt to examine algae as In the endemic areas of Bangladesh cholera epidemics posslble reservoirs of cholera) cleariy indicates that occur twice a year. During epidemics, V. cholerae Ol are blue-green algae could act as a reservoir of V. cholerae isolated from patients as well as from the surface water of 01 in the environment. Before this study, phycologists pond, lake, river, etc. but disappears from the had observed the association of other Gram-negative environment during the interepidemic seasons (17). The bacilli and blue-green algae in the environment, and had reservoirs or sites of survival and multiplication of V. tried to explain the various interdependent mechanisms of cholerae during the interepidemic period are not known. this co-existence (31). Although little information was