The most comprehensive genomic study of syphilis to date has mapped the recent resurgence of the disease around the world. Researchers at the Wellcome Sanger Institute, the UK Health Security Agency, the London School of Hygiene &Tropical Medicine, and their collaborators found almost identical syphilis samples between 14 countries, showing there is widespread international transmission of the disease, particularly within the last 20 years.
The study, published in Nature Microbiology, found that the global syphilis population is made up of two lineages, SS14 and Nichols. Detailed analysis of these lineages provides important insights into the genetic diversity of syphilis, with implications for vaccine design and anti-microbial resistance.
Image credit: Piqsels, free public domain licence
Syphilis is caused by the bacterium Treponema pallidum. It is one of the most common sexually-transmitted infections (STI) globally, with approximately six million infections each year. Syphilis is easily treatable, though symptoms may fade before an individual realises they are infected or may not appear at all. If left untreated syphilis can cause serious long-term health problems.
Syphilis infections occurring during pregnancy can be passed on to the child, causing congenital syphilis. This is the second leading cause of stillbirth globally and can have severe developmental outcomes for children carried to term. It can be prevented through early screening and treatment during pregnancy 1. Congenital syphilis is more common in countries without such screening programmes.
For this study, researchers at the London School of Hygiene & Tropical Medicine (LSHTM) and the Wellcome Sanger Institute coordinated the collection of 726 syphilis samples from 23 countries, including well-sampled areas such as the United States and Western Europe as well as poorly sampled regions such as Central Asia, Australia, and Africa. Researchers at the Sanger Institute sequenced the genome of each sample and conducted phylogenetic and cluster analyses to map the global syphilis population.
Because DNA changes occur at a known and predictable rate over time, the ancestral relationships between different sequences can be established. The researchers found that all the samples came from just two deeply branching lineages, Nichols and SS14. Both lineages are currently circulating in 12 of the 23 countries sampled, and almost identical samples were present in 14 of these countries.
Source: Sanger Institute
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