A non-virulent variant of the deadly Vibrio cholerae O1 strain has likely been present in Haitian aquatic environments for several hundred years, with the potential to become virulent through gene transfer with the toxigenic strain introduced by U.N. peacekeepers, according to scientists at the University of Florida College of Public Health and Health Professions.
“Since the 2010 earthquake and cholera epidemic in Haiti, researchers have debated whether toxigenic Vibrio cholerae was already present in Haiti’s aquatic environments,” said Dr. J. Glenn Morris, director of Florida’s Emerging Pathogens Institute. Dr. Morris is a senior author of the study, published online October 27 in Scientific Reports.
“While the strain responsible for the 2010 cholera epidemic was almost certainly introduced from outside of Haiti by U.N. peacekeeping troops, this study suggests that cholera was present in Haiti at some point in the past, possibly as early as the time of Columbus. These ‘ancient’ strains are now non-toxigenic, and consequently cannot cause cholera. However, their identification raises questions about whether these older strains might interact with the toxigenic V. cholerae O1 introduced by U.N. peacekeepers, becoming virulent in the process,” Dr. Morris said.
Although the V. cholerae species of bacteria are common throughout the world, the toxic strains V. cholerae O1 and V. cholerae O139 are primarily found in Asia and Africa. Investigators isolated two non-toxic V. cholerae O1 strains from estuaries in Port-au-Prince Bay, initially thinking that the isolates were foreign toxigenic strains that had lost their virulence genes. However, on closer examination, they discovered that these isolates were more similar to strains that caused the first cholera pandemics than they were to modern pandemic strains of the bacteria.
“When we used the genomic data to trace the history of these isolates, we found that they shared a common ancestor with the ‘modern’ cholera strains around 1548,” said Dr. Taj Azarian, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health and a recent graduate of the UF doctoral program in epidemiology at the College of Public Health and Health Professions and the College of Medicine. “This was well before any records of cholera in Hispaniola.”
Although the researchers suggest that these cholera strains may have been in Haiti’s aquatic environments since the 1500s, they admit that it is also possible that the strains were introduced at some time after that — becoming endemic, though not pathogenic, well before the 2010 cholera outbreak.
Similarly, the researchers have not yet established the likelihood of modern, toxigenic cholera strains trading genetic information with these older strains, rendering the older strains harmful through the process. The isolates analyzed in the study shed new light on the history of the pathogen, however.
“These non-toxigenic strains are believed to be the progenitor of known toxigenic V. cholerae strains, including both the Classical and El Tor biotypes,” said Dr. Afsar Ali, a research associate professor inFlorida’s Department of Environmental and Global Health and the co-first author of the paper, along with Dr. Azarian.