Diagnosis and evaluation of causative factors for the presence of endemic treponemal disease in a Japanese sub-tropical island population from the Tokugawa period

We present a description and differential diagnosis of pathological lesions observed on skeletal elements found during surface surveys of the Nagabaka site on Miyako-jima Island, Japan. The Nagabaka site served as a bone depository during the Early Modern period (c. AD 1600–1870). We evaluated remains via macroscopic inspection to classify infectious lesions according to criteria in Weston (2008). We also obtained CT scans of three bone elements for more extensive lesion analysis and carried out a differential diagnosis utilizing paleopathological literature. Subsequent investigation yielded convincing evidence of treponemal infection on 23 skeletal elements. Based on known geographical spread and morphological comparisons of lesion patterning, we identified yaws as the pathogen most likely responsible, but refrained from calculating site-wide prevalence due to the taphonomical nature of the sample. Lastly, we review treponemal infection rates in other archaeological sites throughout Southeast Asia and Oceania, and assess similar ecological and cultural factors contributing to the observed pathologies. Nagabaka is the northernmost site in the world where yaws has so far been identified. Located between sites between Mainland China and Western Micronesia where this infection has been previously identified, Miyako-jima holds an important geographical position for research into the historical spread of pathogens.