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Genomics can help estimate risk for cholera epidemics
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Genetic data from a half century worth of cholera isolates can help inform measures to control epidemics, researchers concluded in two recent studies.
In all, the researchers assessed more than 1,200 cholera samples from Africa and Latin America, some from the 1950s.
“These findings have implications for the control of cholera pandemics,” Nicholas R. Thomson, PhD, senior author of one of the studies and a microbiologist at the Wellcome Trust Sanger Institute in Hinxton, United Kingdom, said in a news release. “We are now getting a real sense of how cholera is moving across the globe, and with that information, we can inform improved control strategies as well as basic science to better understand how a simple bacterium continues to pose such a threat to human health.”
The current cholera pandemic is the seventh on record (7P) and began in Indonesia in 1961. It has since spread through south Asia, Africa, Latin America and the Caribbean.
In one of the studies, Francois-Xavier Weill, MD, PhD, from the Institut Pasteur in Paris, France, and colleagues evaluated genomic data from 1,070 Vibrio cholerae isolates spanning 45 African countries.
The researchers analyzed the isolates’ genomes and traced previous epidemics to one expanded lineage of 7P V. cholerae El Tor bacteria (7PET). They found that 7PET was introduced into Africa at least 11 times since 1970.
They also found that the last five introductions included multidrug-resistant lineages, which after 2000 replaced those that had been susceptible to antibiotics. Those five introductions were also from Asia, the researchers said.
Furthermore, the genomic data do not indicate that the cholera epidemics were primarily waterborne.
“Our data do not suggest that aquatic environmental reservoirs are the primary source of epidemic cholera in Africa, as has been suggested,” Weill and colleagues wrote. “Instead, these results highlight the role that humans play in the long-term spread and maintenance of the pathogen, whether by direct (human-to-human) or indirect (pollution of the environment with feces from cholera patients) transmission.”
In the second study, researchers used whole-genome sequencing to compare foreign-borne, pandemic 7PET strains that entered Latin America with local strains.
The researchers focused on two large cholera epidemics that struck Latin America in 1991 and 2010. They found that both were caused by introductions of pandemic 7PET strains.
Specifically, they found that the pandemic V. cholerae lineages were associated with disease patterns that differed with those associated with local strains, and that the pandemic strains were more likely to spur epidemics in the region.
“Pandemic lineages are responsible for massive, explosive epidemics that occur over short periods of time,” Daryl Domman, PhD, from the Sanger Institute, and colleagues wrote.
Domman said the distinction between local and intercontinental strains has public health implications.
“Our data show that, when 7PET pandemic strain enters into Latin America from elsewhere, it can cause massive epidemics like those seen in Peru in the 1990s and Haiti in 2010,” he said in the news release. “However, we now know that other strains already in this region can still make people sick but seem to not have this epidemic potential. Knowing which strain is which allows for an appropriate public health response from regional or national governments.” – by Joe Green
Disclosures: Weill and Domman report no relevant financial disclosures. Please see the studies for all other authors’ relevant financial disclosures.
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