Abstract
The endemicity of cholera in India has been well researched. Among the other endemic areas, Indian subcontinent appears to be the cradle of Vibrio cholerae genovariants, which subsequently spread worldwide. In contrast, all the cholera cases recorded in Russia are of imported origin. In the past century, such importations might result in epidemics, which, however, ended with elimination of toxigenic V. cholerae (TVC) from the affected areas. Currently, the incidence of TVC in water reservoirs or infected returnees from Asian countries are rare events, mostly due to constant surveillance activities. Furthermore, the climatic conditions in the majority of Russian regions are unfavorable for longterm environmental survival of the pathogen. On the other hand, global shifts in climate accompanied by unexpected anomalies in previously stable climatic zones may promote dissemination of imported TVC and emergence of cholera. In some regions of Russia, seasonal weather patterns are pretty similar to Indian. Molecular studies of isolates from diverse territories show that TVC have been introduced into new areas and acquired additional traits, absent in their ancestors.This article describes genomic characteristics of TVC isolates from Russia, India and some other countries. The review is complemented by bioinformatics analysis of important genetic markers to discriminate between clones that emerged in endemic regions and were imported into cholera-free locations. We have found more evidence in support of primary Indian origin of recent genovariants and their ongoing transformation, including the emergence of a new rtxA gene allele with a 60 bp deletion in addition to the previously known null mutation. In certain conditions, TVC could pose a potential threat of spreading epidemic cholera into Russia and other territories. Cholera control requires joint efforts of researchers to learn more about the pathogen at the molecular level for developing effective strategies to protect the humankind throughout the world.
Highlights
The endemicity of cholera in India has been well researched
Present description of the spread of cholera in India and Russia shows that in spite of different current epidemic situation in two countries, some common traits may be found concerning the risks of the disease upsurge
India was rather quickly followed by their migration to Russia, as well as to other countries worldwide, some of which are endemic for cholera
Summary
Cholera is known to be endemic in the South Asian countries, especially in India and Bangladesh, where infections occur every year [19]. Only one evidence of environmental survival of a toxigenic clone has been known, i.e. isolation of clonal V. cholerae strains in Rostov-on-Don from sewage and water from different sites within 2 weeks in 2001 It appears that the pathogen might have originated from patients/carriers and escaped the wastewater treatment process. In Bangladesh cholera maintains an annual cycle with two infection peaks – before and just after monsoon, which is linked to changing physico-chemical and biotic factors These seasonal outbreaks correlate with phytoplankton blooms, which, possibly aid in the increase of cell number of zooplankton-associated TVC [14]. In Russian Federation and neighboring Ukraine, most recorded epidemic outbreaks of cholera took place during hot seasons and were associated with pollution of natural water reservoirs with sewage or fecal contamination by infected humans [3, 17, 25, 26]. The possibility that the longterm “inter-epidemic” period (from 2002 till today) may come to an end in Russia cannot be totally ruled out, because the currently predominating highly virulent new genetic variants of V. cholerae seem to possess better fitness for environmental survival [50]
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