A single introduction of Yersinia pestis to Brazil during the 3rd plague pandemic

Genomic Analysis of Yersinia pestis Strains from Brazil: Search for Virulence Factors and Association with Epidemiological Data

Yersinia pestis, the etiological agent of the plague, is considered a genetically homogeneous species. Brazil is currently in a period of epidemiological silence but plague antibodies are still detected in sentinel animals, suggesting disease activity in the sylvatic cycle. The present study deployed an in silico approach to analyze virulence factors among 407 Brazilian genomes of Y. pestis belonging to the Fiocruz Collection (1966-1997). The pangenome analysis associated several known virulence factors of Y. pestis in clades according to the presence or absence of genes. Four main strain clades (C, E, G, and H) exhibited the absence of various virulence genes. Notably, clade G displayed the highest number of absent genes, while clade E showed a significant absence of genes related to the T6SS secretion system and clade H predominantly demonstrated the absence of plasmid-related genes. These results suggest attenuation of virulence in these strains over time. The cgMLST analysis associated genomic and epidemiological data highlighting evolutionary patterns related to the isolation years and outbreaks of Y. pestis in Brazil. Thus, the results contribute to the understanding of the genetic diversity and virulence within Y. pestis and the potential for utilizing genomic data in epidemiological investigations.

<i>Yersinia pestis</i> Strains of the 1.ORI Line as Etiological Agent of the Plague Pandemic III

Yersinia pestis strains of the 1.ORI lineage originate from China as a result of evolution of the 1.ANT phylogenetic branch. Strains of the biovar orientalis are divided into three major lines of evolution: 1.ORI1, 1.ORI2, 1.ORI3. Lines 1.ORI1 and 1.ORI2 originated in China and then spread across the east and west coasts of India, respectively. Strains of the biovar orientalis have widely spread throughout the world, mainly as a result of introduction by sea. This way, the 1.ORI1 line was imported onto the territory of North America. 1.ORI2 line has spread to Southeast Asia, Africa, Europe, and South America. In addition, the strains of the biovar orientalis were brought to the territory of Australia, however, the formation of natural foci did not occur. The spread of strains to new territories during the third plague pandemic, as a rule, took place with the participation of one strain, which caused epizootics among synanthropic rodents. After that, outbreaks were recorded among the population of port cities, followed by drifting into the countryside and the formation of natural foci under suitable natural conditions. In the absence of such, the plague pathogen was eliminated from natural biotopes, and the formation of a natural focus did not occur. In recent decades, most cases of human plague in the world have been caused by strains of the biovar orientalis (1.ORI). However, the emergence and spread of the evolutionary line “1” is insufficiently studied. Currently, there is a lack of both historical data and strains that are ancestors of modern strains in many countries to clarify the details of the irradiation of strains of the biovar orientalis. As a result, the concepts of dissemination of many evolution branches of the strains, biovar orientalis are in the form of hypotheses to date. In this work, the collection and analysis of literature data on the history and epidemiology of plague over the third pandemic, a search for a connection between epidemic manifestations and the appurtenance of the strains that caused them to certain phylogenetic lineages was carried out.

Small Insertions and Deletions Drive Genomic Plasticity during Adaptive Evolution of Yersinia pestis

The life cycle of Yersinia pestis has changed a lot to adapt to flea-borne transmission since it evolved from an enteric pathogen, Yersinia pseudotuberculosis. Small insertions and deletions (indels), especially frameshift mutations, can have major effects on phenotypes and contribute to virulence and host adaptation through gene disruption and inactivation. Here, we analyzed 365 Y. pestis genomes and identified 2,092 genome-wide indels on the core genome. As recently reported in Mycobacterium tuberculosis, we also detected "indel pockets" in Y. pestis, with average complexity scores declining around indel positions, which we speculate might also exist in other prokaryotes. Phylogenic analysis showed that indel-based phylogenic tree could basically reflect the phylogenetic relationships of major phylogroups in Y. pestis, except some inconsistency around the Big Bang polytomy. We observed 83 indels arising in the trunk of the phylogeny, which played a role in accumulation of pseudogenes related to key metabolism and putatively pathogenicity. We also discovered 32 homoplasies at the level of phylogroups and 7 frameshift scars (i.e., disrupted reading frame being rescued by a second frameshift). Additionally, our analysis showed evidence of parallel evolution at the level of genes, with sspA, rpoS, rnd, and YPO0624, having enriched mutations in Brazilian isolates, which might be advantageous for Y. pestis to cope with fluctuating environments. The diversified selection signals observed here demonstrates that indels are important contributors to the adaptive evolution of Y. pestis. Meanwhile, we provide potential targets for further exploration, as some genes/pseudogenes with indels we focus on remain uncharacterized. IMPORTANCE Yersinia pestis, the causative agent of plague, is a highly pathogenic clone of Yersinia pseudotuberculosis. Previous genome-wide SNP analysis provided few adaptive signatures during its evolution. Here by investigating 365 public genomes of Y. pestis, we give a comprehensive overview of general features of genome-wide indels on the core genome and their roles in Y. pestis evolution. Detection of "indel pockets," with average complexity scores declining around indel positions, in both Mycobacterium tuberculosis and Y. pestis, gives us a clue that this phenomenon might appear in other bacterial genomes. Importantly, the identification of four different forms of selection signals in indels would improve our understanding on adaptive evolution of Y. pestis, and provide targets for further physiological mechanism researches of this pathogen. As evolutionary research based on genome-wide indels is still rare in bacteria, our study would be a helpful reference in deciphering the role of indels in other species.

Yersinia pestis: the Natural History of Plague

The Gram-negative bacterium Yersinia pestis is responsible for deadly plague, a zoonotic disease established in stable foci in the Americas, Africa, and Eurasia. Its persistence in the environment relies on the subtle balance between Y. pestis-contaminated soils, burrowing and nonburrowing mammals exhibiting variable degrees of plague susceptibility, and their associated fleas. Transmission from one host to another relies mainly on infected flea bites, inducing typical painful, enlarged lymph nodes referred to as buboes, followed by septicemic dissemination of the pathogen. In contrast, droplet inhalation after close contact with infected mammals induces primary pneumonic plague. Finally, the rarely reported consumption of contaminated raw meat causes pharyngeal and gastrointestinal plague. Point-of-care diagnosis, early antibiotic treatment, and confinement measures contribute to outbreak control despite residual mortality. Mandatory primary prevention relies on the active surveillance of established plague foci and ectoparasite control. Plague is acknowledged to have infected human populations for at least 5,000 years in Eurasia. Y. pestis genomes recovered from affected archaeological sites have suggested clonal evolution from a common ancestor shared with the closely related enteric pathogen Yersinia pseudotuberculosis and have indicated that ymt gene acquisition during the Bronze Age conferred Y. pestis with ectoparasite transmissibility while maintaining its enteric transmissibility. Three historic pandemics, starting in 541 AD and continuing until today, have been described. At present, the third pandemic has become largely quiescent, with hundreds of human cases being reported mainly in a few impoverished African countries, where zoonotic plague is mostly transmitted to people by rodent-associated flea bites.