Environmental and Epidemiological Aspects of V. cholerae O1 Contamination of Water Bodies in the Republic of Kalmykia

Abstract

Background: Within the framework of cholera surveillance in the Russian Federation, annual isolation of nontoxigenic V. cholerae O1 strains from water bodies is registered in the Republic of Kalmykia. This fact is the rationale for the present study and analysis of data on contamination of water bodies with V. cholerae O1 with account for some environmental and quality indicators of water bodies used for recreational purposes. Objective: To study contamination of water bodies with V. cholerae O1 as a component of cholera control surveillance in the Republic of Kalmykia. Materials and methods: We used notifications issued by Offices of the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing (Rospotrebnadzor) in the constituent entities of the Russian Federation, passports for V. cholerae O1 strains, and information from “Cholera vibrios. Russia” database for 1991–2019. Results: In the 1970s, 1980s and 1990s, several outbreaks, sporadic and single imported cases of cholera were registered in the republic. The total of 446 strains of V. cholerae O1 El Tor were isolated during the analyzed period. The PCR analysis identified them as V. cholerae O1 ctxA–tcpA– and V. cholerae O1 ctxA– tcpA+. We observed an increasing trend in the number of isolated strains with the approximation coefficient of 0.374 against its general decrease in the country in 1991–2019. Strains were isolated annually, mainly from the Elista River, Zayachy Pond and other water bodies with poor microbiological and chemical water quality parameters. V. cholerae O1 ctxA– tcpA+ were isolated mainly at the wastewater discharge sites, which indicated their imported origin, along with V. cholerae O1 ctxA– tcpA– with InDel and PCR genotypes not previously found in this region. We consider the contamination of water bodies with V. cholerae O1 ctxA– tcpA– and V. cholerae O1 ctxA– tcpA+ as prerequisites for possible deterioration of the local epidemiological situation due to cholera importation from endemic areas. Conclusion: When analyzing the pollution of water bodies in the Republic of Kalmykia with V. cholerae O1, we established a long-term annual isolation of cholera vibrios from some water bodies in the city of Elista, including Elistinka river, Zayachy and Kolonsky ponds, notorious for poor microbiological and chemical water quality indicators. The contamination was mainly attributed to domestic wastewater discharge and poorly treated effluents of sewage treatment plants into the Elistinka river within the city boundaries, as well as watercourses from hollows. This proves the imported origin of the bacterium confirmed by isolation of V. cholerae O1 ctxA– tcpA– with InDel- and PCR-genotypes not previously found in this region.