Abstract
Vibrio cholerae, the causative agent of pandemic cholera, is abundant in marine and freshwater environments. Copepods and chironomids are natural reservoirs of this species. However, the ways V. cholerae is globally disseminated are as yet unknown. Here we review the scientific literature that provides evidence for the possibility that some fish species may be reservoirs and vectors of V. cholerae. So far, V. cholerae has been isolated from 30 fish species (22 freshwater; 9 marine). V. cholerae O1 was reported in a few cases. In most cases V. cholerae was isolated from fish intestines, but it has also been detected in gills, skin, kidney, liver and brain tissue. In most cases the fish were healthy but in some, they were diseased. Nevertheless, Koch postulates were not applied to prove that V. cholerae and not another agent was the cause of the disease in the fish. Evidence from the literature correlates raw fish consumption or fish handling to a few cholera cases or cholera epidemics. Thus, we can conclude that V. cholerae inhabits some marine and freshwater fish species. It is possible that fish may protect the bacteria in unfavorable habitats while the bacteria may assist the fish to digest its food. Also, fish may disseminate the bacteria in the aquatic environment and may transfer it to waterbirds that consume them. Thus, fish are reservoirs of V. cholerae and may play a role in its global dissemination.
Highlights
The devastating disease, cholera, is known to occur globally causing epidemics and pandemics
Halpern et al (2008) raised the hypothesis that fish that feed on copepods and chironomids, and waterbirds that may feed on these invertebrates and consume fish as well, may be reservoirs and vectors of V. cholerae
V. cholerae was isolated from internal organs of diseased ayu (Plecoglossus altivelis) and guppy fish (Poecilia reticulate) in Japan and Iran, respectively (Yamanoi et al, 1980; Kiiyukia et al, 1992; Kiani et al, 2016) and from Nile tilapia (Oreochromis niloticus) that were cultured in floating cages in Thailand (Dong et al, 2015) (Table 1)
Summary
The devastating disease, cholera, is known to occur globally causing epidemics and pandemics. The strains were detected in the fish intestine after the fish were exposed to the bacteria (Table 1). V. cholerae O1 isolates, positive to ctxA and tcpA genes were detected from two marine fish in Cochin, India (no details were given as to the fish species) (Kumar and Lalitha, 2013).
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