Toxigenic Vibrio cholerae evolution and establishment of reservoirs in aquatic ecosystems

Abstract

The spread of cholera in the midst of an epidemic is largely driven by direct transmission from person to person, although it is well-recognized thatVibrio choleraeis also capable of growth and long-term survival in aquatic ecosystems. While prior studies have shown that aquatic reservoirs are important in the persistence of the disease on the Indian subcontinent, an epidemiological view postulating that locally evolving environmentalV. choleraecontributes to outbreaks outside Asia remains debated. The single-source introduction of toxigenicV. choleraeO1 in Haiti, one of the largest outbreaks occurring this century, with 812,586 suspected cases and 9,606 deaths reported through July 2018, provided a unique opportunity to evaluate the role of aquatic reservoirs and assess bacterial transmission dynamics across environmental boundaries. To this end, we investigated the phylogeography of both clinical and aquatic toxigenicV. choleraeO1 isolates and show robust evidence of the establishment of aquatic reservoirs as well as ongoing evolution ofV. choleraeisolates from aquatic sites. Novel environmental lineages emerged from sequential population bottlenecks, carrying mutations potentially involved in adaptation to the aquatic ecosystem. Based on such empirical data, we developed a mixed-transmission dynamic model ofV. cholerae, where aquatic reservoirs actively contribute to genetic diversification and epidemic emergence, which underscores the complexity of transmission pathways in epidemics and endemic settings and the need for long-term investments in cholera control at both human and environmental levels.

Modular Molecular Weaponry Plays a Key Role in Competition Within an Environmental Vibrio cholerae Population

“…Environmental populations of Vibrio cholerae , the etiological agent of cholera, are composed of different toxigenic and non-toxigenic lineages living together in brackish water habitats ( Pretzer et al, 2017 ; Mavian et al, 2020 ). Among their competitive arsenal, shared with ∼25% of all Gram-negative bacteria ( Bingle et al, 2008 ), is the type VI secretion system (T6SS).…”

Phylogeography of the marine pathogen, Vibrio vulnificus, revealed the ancestral scenarios of its evolution

“…Similarly, persistent aquatic environmental reservoirs for V . cholerae O1 are present in Asia, causing a disease that has recurrently manifested in seven worldwide pandemics originating from Asia (Colwell & Huq, 1994; Mavian et al, 2020; Weill et al, 2017).…”

“…However, ML methodologies are not equally effective for bacteria, detecting less ancestral states (nodes in the tree) than other approaches based on Bayesian inference. Nevertheless, and rather interestingly ML‐based methodology has been recently used for studying the evolution of Vibrio cholerae reservoirs in aquatic ecosystems (Mavian et al, 2020).…”

Endemic Cholera in India and Imported Cholera in Russia: What is Common?

“…In endemic countries, cholera continues to occur due to hot climate, poor sanitation and natural reservoirs of infection. Survival of TVC in such environments is thought to be the possible reason for recurrent annual epi demics in the Indian subcontinent [33]. Several investigations carried out in India during cholera outbreaks showed that TVC were present in samples collected from the affected areas [34][35][36].…”