RELATIONSHIP BETWEEN PLANKTON POPULATION AND THE SURVIVAL OF EPIDEMIC VIBRIO CHOLERAE IN BANGLADESH

Abstract

In spite of the considerable number of critical work that has been conducted on the diarrhoea causing Vibrio cholarae bacterium, the ecological role of it’s habitat, survival and association with plankton in Bangladesh still little known. The study was conducted at twelve ponds, one canal and one river ecosystems from two geographical locations i.e., Mathbaria and Chhatak, of Bangladesh between the year 2013 and 2014 to assess the role of selected climatic and limnological parameters on the Vibrio cholarae and plankton population. Sampling was done on weekly basis during the outbreak season of cholera, while fortnightly in non-infectious period. From the coastal seven ponds of Mathbaria 86 species of zooplankton was recorded, of which 27 species of protozoa, 43 species of rotifera, 8 species of copepod and 8 species of cladocera. Freshwater ponds and river of Chhatak exhibited in total of 100 species of zooplankton of which 14 species belonged to the phylum protozoa, 58 species of rotifera, 9 species of copepod and 19 species of cladocera. In Mathbaria two peak seasons of cholera existed, summer (March-May) and autumn (September-November) where site-2 (pond), site-8 (local canal) and site-11 (pond) were recognized as suspected V. cholerae contaminated ponds due to the isolation of toxigenic V. cholerae O1 from these water bodies. The total zooplankton, specially crustacean plankton was dominantly recorded during peak season of cholera in all water bodies. In Mathbaria, crustacean planktonic nauplii were recorded in highest number in both peak infection seasons. In non-contaminated ponds ponds (sites-5, 7 and 9) protozoa, rotifer and nauplii were dominant in the peak season of cholera. In Chhatak, peak season of cholera infection was occurred only once in autumn (September-November). Three sampling sites in Chhatak as site-1 (pond), site-10 (Surma River) and site-12 (pond) were suspected as V. cholerae contaminated. During the study in Mathbaria and Chhatak seasonal species of copepod Cyclops sp., Diaptomus sp. and cladocera Diaphanosoma sp.were dominant plankton in two areas. Hydroclimatological factors like total rainfall in Mathbaria started to increase during summer peak (April) and then decrease at the end of autumn peak (November). On the other hand, in Chhatak total rainfall was highest during peak season (September-October) of cholera in the 2013. It was aided by highest air temperature during the peak seasons of cholera in Mathbaria and Chhatak. In pond ecosystem, micronutrients like nitrogen and phosphorus was found to be highest to improve primary productivity during peak V. cholerae season. Laboratory based microcosm study on copepods from three water sources inoculated with the pure culture of toxigenic Vibrio cholerae O1 revealed that the count of bacteria was increased with the increased production of nauplii. Direct Fluorescent Antibody (DFA) and Scanning Electron Microscopy (SEM) images exhibits positive association of Vibrio cholerae O1 with extracted crab and shrimp chitin. Considering the biomass, the amount of minimum nauplii biomass was found to be 94.3 g per cubic meter dry weight during peak season in the water samples. From this study, it is evident that the hydroclimatic factors in association with the limnological parameters is creating a favorable condition for the emergence and survibility of V. cholerae bacteria in the. The water temperature, crustacean zooplankton abundance with certain biomass under favourable nutrients state in the contaminated water bodies help in ensuring the maximum environmental condition for Vibrio cholerae survibility. In spite of long geographical distances of coastal Mathbaria water bodies are more vulnerable to contamination and disease spread than freshwater Chhatak waters. However, the environmental challenges being overcome by the bacterium during the infection season.