Over the last few years, genomic studies on Yersinia pestis, the causative agent of all known plague epidemics, have considerably increased in numbers, spanning a period of about 5,000 y. Nonetheless, questions concerning historical reservoirs and routes of transmission remain open. Here, we present and describe five genomes from the second half of the 14th century and reconstruct the evolutionary history of Y. pestis by reanalyzing previously published genomes and by building a comprehensive phylogeny focused on strains attributed to the Second Plague Pandemic (14th to 18th century). Corroborated by historical and ecological evidence, the presented phylogeny, which includes our Y. pestis genomes, could support the hypothesis of an entry of plague into Western European ports through distinct waves of introduction during the Medieval Period, possibly by means of fur trade routes, as well as the recirculation of plague within the human population via trade routes and human movement.
The Second Plague Pandemic started in the mid-14th century and lasted until the 19th century. Its beginning in Europe is marked by a major epidemic event commonly referred to as the Black Death (1346–1353), which ultimately led to the death of at least 30% of the European population . The Black Death reached Western Europe in October 1347 through infected Genoese galleys arriving from Caffa and spread over multiple routes and directions, after having reached the thriving trade center of Constantinople. Two other pandemics are historically attested, the first, starting in 541–542 CE with the Justinian Plague and lasting in Europe until the mid of the eighth century, and the third, which originated in 1772 in the Yunnan Province, southwest China, and is still ongoing.
Plague is a zoonosis, which occasionally spills over to human populations. However, it is primarily a disease of wildlife and is maintained in reservoirs, which nowadays are present on all continents, with the exception of Australia and Western Europe. While our knowledge of modern plague reservoirs and their hosts is extensive, it remains unclear which plague reservoir(s) was the origin of the epidemics recorded in Europe throughout its history. Consequently, we are also lacking knowledge of the main routes and mechanisms of transmission during the historical pandemics. Two scenarios have been suggested in previous studies: (i) After a first introduction during the Black Death, plague periodically spilled over from one or more reservoirs located in Western Europe, from where it was later (re)introduced to China and gave rise to the Third Pandemic ; (ii) plague was repeatedly introduced to Western Europe from a reservoir located in Eastern Europe/Central Asia and spread via commercial trade routes and human movement . These two scenarios are mutually exclusive regarding the establishment of local European reservoir of plague during the Second Pandemic.
In this study, we provide five sequenced ancient genomes recovered from four archeological sites: Abbadia San Salvatore (BSS) (Italy), Saint-Laurent-de-la-Cabrerisse (SLC) (France), Bergen op Zoom (BER) (The Netherlands), and Oslo (OSL) (Norway). The presented genomes all date to the 14th century and represent the focus of our analysis. By supplying additional genomic data of ancient strains recovered from victims of historical epidemics, our study can improve the resolution of the Yersinia pestis phylogeny and can contribute to the discussion on transmission routes and reservoir establishments during historical pandemics. Using state-of-the-art bioinformatics methods, we evaluated the evolutionary history of Y. pestis by incorporating the data reported in this study into a revised phylogeny. We evaluated our results in light of historical, epidemiological, and ecological studies to improve our understanding of the fully documented spectrum of the dynamics at work during the early decades of the Second Plague Pandemic.
Source: med.news.am
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