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Elimination strategy for yaws

Genome sequencing has shed light on the re-emergence of the bacterium that causes yaws – a neglected tropical disease of the skin, bones and joints. 

The re-emergence followed a mass drug administration (MDA) campaign that aimed to eliminate the disease in Papua New Guinea.

Yaws, caused by the bacterium Treponema pallidum subspecies pertenue (TPP), can cause chronic disfigurement and disability. 

Despite global efforts, it remains common in tropical areas in some of the world’s poorest countries, affecting millions of people. 

The World Health Organization is currently carrying out campaigns to eradicate yaws using MDA of the antibiotic azithromycin.

An MDA campaign on Lihir Island, Papua New Guinea, in 2013 reached 83% of the population (15,000-18,000 people) and was initially successful, dramatically reducing the incidence of the disease, but after two years, cases of the disease starting increasing.

In this new study, researchers sequenced the genomes of bacteria from 20 swab samples taken during the follow-up of the MDA campaign in Lihir. The aim was to further understand the re-emergence following the MDA and inform future strategies.

Comparing the DNA sequences of the TPP bacteria, the team constructed phylogenetic “family” trees to map their evolution. DNA sequences change over time at a constant rate as organisms evolve, and so it is possible to determine the relatedness of individual samples and relate that back to the patient and possible routes of infection. 

They found that, rather than re-emergence being due to a single source, missed case, or reintroduction, the re-emergence of cases after MDA was actually caused by at least three distinct TPP lineages. The most likely explanation for this is that these were caused by latent infections in people, without symptoms, who didn’t receive the treatment.

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