Why vaccines alone won’t beat dysentery

"Unlike other Shigella species, we have found that S. flexneri is able to survive in a geographic region, independent of human contact. This tells us that eradicating the bacteria in people through vaccination alone, although important, will not be enough," says Clare Barker. (Credit: Sacca/Flickr)

Despite improvements in sanitation and clean water access, dysentery remains a major public health burden that most often affects children in low-income countries.

New research uses genomic techniques to reveal more about the bacteria Shigella flexneri, a leading cause of the disease.

Researchers sequenced the DNA of Shigella flexneri from samples taken from Africa, Asia, and South and Central America, along with samples from historical collections dating back to 1913.

They discovered that the bacteria are able to persist in the local environment, enabling it to colonize regions for tens or hundreds of years.

More importantly, the work also showed that the bacteria can swap its serotype—a key part of its outer coating that is “seen” by the immune system—which could render potential vaccines useless in the fight against this disease.

“Understanding how S. flexneri has changed and spread in endemic countries is vital for developing and targeting interventions more effectively,” says study leader Thomas Connor of the Cardiff University School of Biosciences.

“By using genomics we have been able to unambiguously characterise this pathogen on a global scale and our findings redefine what we knew about this bacteria,” he adds.

The genomic analysis also reveals that using traditional microbiological techniques such as serotyping to understand the spread and diversity of the bacteria is unhelpful for planning public health campaigns and for creating effective vaccines.

“Unlike other Shigella species, we have found that S. flexneri is able to survive in a geographic region, independent of human contact. This tells us that eradicating the bacteria in people through vaccination alone, although important, will not be enough,” according to Clare Barker, who worked in Connor’s group on the research.

The insights produced from sequencing the whole genome also offer new options for more targeted vaccine production.

“Our findings show that major lineages of S. flexneri are able to switch between serotypes and thereby evade the protective effect of serotype-based vaccination approaches,” says Professor Nick Thomson, senior author from the Wellcome Trust Sanger Institute.

“By using genome sequencing to study the species at the highest resolution possible, we are able to identify clear lineages of bacteria based on the virulence genes they carry.

“These lineages can then be targeted more effectively for intervention whether that be through vaccine development and/or alternative strategies,” he adds.

The findings appear in the journal eLife.

Source: Cardiff University