Genomic surveillance has revealed the re-emergence of the bacterium that causes yaws, scientists have announced.
Cases of yaws in Papua New Guinea have been revealed by researchers at the Wellcome Sanger Institute, the London School of Hygiene & Tropical Medicine, the Fight Aids and Infections Disease Foundation, Spain, the University of Washington and the University of Papua New Guinea, despite a mass drug administration (MDA) campaign that aimed to eliminate the disease.
Their findings are reported in Lancet Microbe and the team says the results of the surveillance will influence the global elimination strategy for yaws.
Yaws is caused by the bacterium Treponema pallidum subspecies pertenue (TPP) and can cause chronic disfigurement and disability. It affects mainly children and infection can lead to debilitating ulcers.
The disease remains common in tropical areas in some of the world’s poorest countries and the World Health Organisation (WHO) is carrying out campaigns to eradicate it using Mass Drug Administration of azithromycin.
An MDA campaign on Lihir Island, Papua New Guinea, in 2013 reached 83% of the population of between 15-18,000 people.
Although it was initially successful, dramatically reducing the incidence of the disease, cases of the disease started increasing again after two years.
In this new study, Sanger researchers sequenced the genomes of bacteria from 20 swab samples taken during the follow up of the MDA campaign in Lihir to help further understand the re-emergence.
The team compared the DNA sequences of the TPP bacteria and constructed phylogenetic “family” trees to map their evolution.
They found that the re-emergence of cases after MDA was caused by at least three distinct TPP lineages, which was most likely caused by latent infections in asymptomatic people who did not receive the treatment.
They say this finding has important implications for disease control and has led them to call for strategies to maximise MDA population coverage to reduce the number of people who are missed by these treatments who may have latent infections.
The researchers also recommend intensive post-MDA surveillance for detection of “the last yaws cases” and to control onward transmission of new infections.
Of the three lineages that were linked to the re-emergence, one became resistant to azithromycin during the study, which led the researchers to combine the genomic data with epidemiological data about the movement and interactions of people in the region. This showed that resistance to azithromycin can evolve and spread rapidly in TPP.
The authors recommend careful monitoring following an MDA to enable the rapid detection of azithromycin resistance that could compromise MDA campaigns.
First author Dr Mathew Beale, from the Wellcome Sanger Institute, said: "The development of antibiotic resistance is worrying, but the fact that it only occurred once after a mass drug administration is positive news. We still need to be very concerned about resistance, but it may be possible to manage it.”
Senior author Dr Oriol Mitjà, of Lihir Medical Center, Papua New Guinea and the Fight Aids and Infections Disease Foundation, added: “While yaws doesn’t kill, it causes significant disease in thousands of children around the world. Yet it is easily treatable. Following up on treatment trials is vital – we need to know where and why the bacteria are re-emerging. The results from this study are influencing the next steps and approaches we take to eradicate this disease.”
Lancet Microbe 7 October 2020
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