Doctoral Dissertation Research: Tracing the origin of infectious disease: A comparative paleogenomics study of Treponema pallidum

Syphilis is a sexually transmitted infection (STI) caused by Treponema pallidum subp. pallidum bacteria. It has recently reemerged as an urgent worldwide health crisis. The origin of the disease has been a mystery since its sudden appearance in Europe at the end of the 15th century and its subsequent rapid global spread. It has long been debated whether syphilis was introduced to Europe, perhaps from the Americas, or evolved from a form of treponemal infection that had been in Europe all along. Graduate student Ziyu Wang and collaborators at The Pennsylvania State University will take a multi-faceted approach to investigate the pathogen's genetic diversity over the past 500 years in Europe to explore several possibilities to explain syphilis' origin in Europe. The current T. pallidum pathogens - associated with several related diseases - likely represent only the most successful or recently emerged genetic variants. Examined through an anthropological lens, ancient genomes when considered within the context of human sociocultural systems yield clues about the processes through which pathogens have achieved their evolutionary success. Ultimately a more informed understanding of the factors that contribute to the complex and dynamic interactions between humans and their pathogens provides a deep-time foundation for predicting the evolutionary trajectories of modern infectious pathogens and human responses. Today, as in the past, STI-related stigma has done much to interfere with the development and implementation of effective intervention programs. Lessons learned from historic epidemics and the public response will provide valuable tools for training healthcare professionals, STI high-risk groups, and the public.

To untangle syphilis' origin, its evolution, and its worldwide spread, the research team will sequence T. pallidum genomes from representative specimens sampled from temporally and socially well-characterized European skeletal assemblages dating to the 16th to 19th centuries. Ancient T. pallidum has previously not been well studied because of the limited ability of conventional genetic techniques (e.g., polymerase chain reaction) to recover highly-degraded ancient pathogen DNA. Here a sensitive targeted hybridization capture technique will be used to recover complete, or near-complete, ancient T. pallidum genomes. By comparing temporally known ancient pathogen genomes with their modern equivalents, the research team can track the sequential changes that occurred in the pathogen's genetic history. Doing so will narrow the possible evolutionary scenarios for the origin of syphilis and point to when the pathogen variant that causes syphilis first emerged.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.