Genome sequencing finds Haitian cholera's source

A recent whole-genome sequencing study of Haiti’s cholera outbreak strain has produced strong evidence that the disease was brought into the country by United Nations peacekeepers from Nepal.

The study, published in mBio, the online journal of the American Society for Microbiology, was led by a group at the Translational Genomics Research Institute, based in Flagstaff, Arizona, according to CIDRAP News. Dr. Paul Keim, who used similar tracking techniques while investigating the 2001 anthrax attacks, co-authored the study.

Researchers used whole-genome sequence typing, pulse-field gel electrophoresis and antimicrobial susceptibility testing to characterize a total of 24 isolates of the cholera bacterium from five districts in Nepal and several more from Haiti’s outbreak. They found that a cholera outbreak occurred in Nepal in July 2010 and was controlled by approximately August, right before the soldiers left the country.

Antimicrobial susceptibility and PFGE tests supported an epidemiological link between the Nepalese and Haitian isolates. Both groups of isolates were susceptible to the antibiotic tetracycline but resistant to trimethoprim, sulfamethoxazole and nalidixic acid, and both showed a decreased susceptibility to ciprofloxacin, CIDRAP News reports.

Further genome testing demonstrated that the Nepalese isolates fell into four related clusters, one of whose isolates were nearly identical to the Haitian isolates.

The identification of DNA subclades in the cholera isolates from Nepal suggests that the disease is prevalent there and that major hygiene improvements and other investments are needed to stem the spread of the disease.