No particular genomic features underpin the dramatic economic consequences of 17th century plague epidemics in Italy

Ancient Yersinia pestis genomes lack the virulence-associated YpfΦ prophage present in modern pandemic strains

Yersinia pestis is the causative agent of at least three major plague pandemics (Justinianic, Medieval and Modern). Previous studies on ancient Y. pestis genomes revealed that several genomic alterations had occurred approximately 5000-3000 years ago and contributed to the remarkable virulence of this pathogen. How a subset of strains evolved to cause the Modern pandemic is less well-understood. Here, we examined the virulence-associated prophage (YpfΦ), which had been postulated to be exclusively present in the genomes of strains associated with the Modern pandemic. The analysis of two new Y. pestis genomes from medieval/early modern Denmark confirmed that the phage is absent from the genome of strains dating to this time period. An extended comparative genome analysis of over 300 strains spanning more than 5000 years showed that the prophage is found in the genomes of modern strains only and suggests an integration into the genome during recent Y. pestis evolution. The phage-encoded Zot protein showed structural homology to a virulence factor of Vibrio cholerae. Similar to modern Y. pestis, we observed phages with a common origin to YpfΦ in individual strains of other bacterial species. Our findings present an updated view on the prevalence of YpfΦ, which might contribute to our understanding of the host spectrum, geographical spread and virulence of Y. pestis responsible for the Modern pandemic.

Improving the extraction of ancient Yersinia pestis genomes from the dental pulp

Ancient DNA preserved in the dental pulp offers the opportunity to characterize the genome of some of the deadliest pathogens in human history. However, while DNA capture technologies help, focus sequencing efforts, and therefore, reduce experimental costs, the recovery of ancient pathogen DNA remains challenging. Here, we tracked the kinetics of ancient Yersinia pestis DNA release in solution during a pre-digestion of the dental pulp. We found that most of the ancient Y. pestis DNA is released within 60 min at 37°C in our experimental conditions. We recommend a simple pre-digestion as an economical procedure to obtain extracts enriched in ancient pathogen DNA, as longer digestion times release other types of templates, including host DNA. Combining this procedure with DNA capture, we characterized the genome sequences of 12 ancient Y. pestis bacteria from France dating to the second pandemic outbreaks of the 17^th and 18^th centuries Common Era.

Epidemiological Characteristics of Human and Animal Plague in Yunnan Province, China, 1950 to 2020

This study analyzed the epidemiological characteristics of 3,464 human plague cases and the distribution pattern of 4,968 Yersinia pestis isolates from humans, hosts, and vector insects from 1950 to 2020 among two natural plague foci in Yunnan Province, China. These foci include the Rattus flavipectus plague focus of the Yunnan, Guangdong, and Fujian provinces and the Apodemus chevrieri-Eothenomys miletus plague focus of the highlands of northwestern Yunnan Province. The case fatality rate for plague in humans was 18.39% (637/3,464), and the total isolation rate of Y. pestis was 0.17% (4,968/2,975,288). Despite that the frequency of human cases declined rapidly, the animal plague fluctuated greatly, alternating between activity and inactivity in these foci. The tendency among human cases can be divided into 4 stages, 1950 to 1955, 1956 to 1989, 1990 to 2005, and 2006 to 2020. Bubonic plague accounted for the majority of cases in Yunnan, where pneumonic and septicemic plague rarely occurred. The natural plague foci have been in a relatively active state due to the stability of local ecology. Dense human population and frequent contact with host animals contribute to the high risk of human infection. This study systematically analyzed the epidemic pattern of human plague and the distribution characteristics of Y. pestis in the natural plague foci in Yunnan, providing a scientific basis for further development and adjustment of plague prevention and control strategies. IMPORTANCE Yunnan is the origin of the third plague pandemic. The analysis of human and animal plague characteristics of plague foci in Yunnan enlightens the prevention and control of the next plague pandemics. The plague characteristics of Yunnan show that human plague occurred when animal plague reached a certain scale, and strengthened surveillance of animal plague and reducing the density of host animals and transmission vectors contribute to the prevention and control of human plague outbreaks. The phenomenon of alternation between the resting period and active period of plague foci in Yunnan further proves the endogenous preservation mechanism of plague.

A 16th century Escherichia coli draft genome associated with an opportunistic bile infection

Escherichia coli – one of the most characterized bacteria and a major public health concern – remains invisible across the temporal landscape. Here, we present the meticulous reconstruction of the first ancient E. coli genome from a 16^th century gallstone from an Italian mummy with chronic cholecystitis. We isolated ancient DNA and reconstructed the ancient E. coli genome. It consisted of one chromosome of 4446 genes and two putative plasmids with 52 genes. The E. coli strain belonged to the phylogroup A and an exceptionally rare sequence type 4995. The type VI secretion system component genes appears to be horizontally acquired from Klebsiella aerogenes, however we could not identify any pathovar specific genes nor any acquired antibiotic resistances. A sepsis mouse assay showed that a closely related contemporary E. coli strain was avirulent. Our reconstruction of this ancient E. coli helps paint a more complete picture of the burden of opportunistic infections of the past.

Ancient DNA from an Italian mummy’s gallstone provides insight into opportunistic E. coli infection.

Differential word expression analyses highlight plague dynamics during the second pandemic

Research on the second plague pandemic that swept over Europe from the fourteenth to nineteenth centuries mainly relies on the exegesis of contemporary texts and is prone to interpretive bias. By leveraging certain bioinformatic tools routinely used in biology, we developed a quantitative lexicography of 32 texts describing two major plague outbreaks, using contemporary plague-unrelated texts as negative controls. Nested, network and category analyses of a 207-word pan-lexicome, comprising overrepresented terms in plague-related texts, indicated that 'buboes' and 'carbuncles' are words that were significantly associated with the plague and signalled an ectoparasite-borne plague. Moreover, plague-related words were associated with the terms 'merchandise', 'movable', 'tatters', 'bed' and 'clothes'. Analysing ancient texts using the method reported in this paper can certify plague-related historical records and indicate the particularities of each plague outbreak, which can inform on the potential sources for the causative Yersinia pestis.

Assessing the origins of the European Plagues following the Black Death: A synthesis of genomic, historical, and ecological information

The second plague pandemic started in Europe with the Black Death in 1346 and lasted until the 19th century. Based on ancient DNA studies, there is a scientific disagreement over whether the bacterium, Yersinia pestis, came into Europe once (Hypothesis 1) or repeatedly over the following four centuries (Hypothesis 2). Here, we synthesize the most updated phylogeny together with historical, archeological, evolutionary, and ecological information. On the basis of this holistic view, we conclude that Hypothesis 2 is the most plausible. We also suggest that Y. pestis lineages might have developed attenuated virulence during transmission, which can explain the convergent evolutionary signals, including pla decay, that appeared at the end of the pandemics.