Status and analysis of undetected plague cases in Yunnan Province, China.

Background: The virulence of Yersinia pestis strains in the Rattus flavipectus plague focus is relatively low. The purpose of this study was to investigate the undetected, sporadic plague cases in plague foci and provide the basis for plague prevention and control. Methods: A 3-year-old plague-confirmed case was investigated in the R. flavipectus plague focus of Yunnan Province in 2020 due to the intensive screening for fever symptoms during the coronavirus disease 2019 (COVID-19) pandemic. Epidemiological investigation, laboratory testing, and clinical treatment were conducted for the case. The expanded survey was carried out around the case within a 7-km radius, including the resident population, domesticated dogs, and rats. PCR and indirect hemagglutination tests were performed on the collected samples. Results: The isolation rates of Y. pestis were 100.0% (7 out of 7) in dead rats and 4.00% (3 out of 75) in live rats in the survey area of the foci. A total of 5.00% (6 out of 120) of the domesticated dogs were F1 antibody positive. Nine local people were determined for plague infection recently (0.92%, 9 out of 978). The locations of human cases coincided with the Y. pestis epidemic area among the animals. Conclusion: This study discovered the existence of plague cases that had not been detected by routine surveillance in the R. flavipectus plague focus, and the actual epidemic of human infection may be underestimated.

Symbiosis of a lytic bacteriophage and Yersinia pestis and characteristics of plague in Marmota himalayana.

Surveillance for animal plague was conducted in the Marmota himalayana plague focus of the Qinghai-Tibet Plateau from 2020 to 2023. A 22.89% positive rate of serum F1 antibody was detected in live-caught marmots, alongside a 43.40% incidence of Yersinia pestis isolation from marmot carcasses. Marmot carcasses infected with plague exhibited a significantly higher spleen-somatic index (P < 0.05). Twenty-one Y. pestis-specific phages were isolated, among which one Y. pestis lytic phage (AKS2022HT87GU_phi) was isolated from the bone marrow of a marmot carcass (no. AKS2022HT87) and was found to be symbiotic with Y. pestis. Microscopy revealed the coexistence of lysed and non-lysed colonies of Y. pestis AKS2022HT87. Genome-wide analysis showed that certain strains of the Y. pestis AKS2022HT87 carried phage DNA fragments consistent with phage AKS2022HT87GU_phi. The rare symbiotic relationship between a lytic phage and Y. pestis observed in vitro was highlighted in this study, laying the basis for further exploring the relationship between Y. pestis and its bacteriophages.IMPORTANCEBacteriophages and host bacteria commonly coexist in vivo or in soil environments through complex and interdependent microbial interactions. However, recapitulating this symbiotic state remains challenging in vitro due to limited medium nutrients. In this work, the natural symbiosis between Yersinia pestis and specific phages has been discovered in a Marmota himalayana specimen. Epidemiological analysis presented the characteristics of the Y. pestis and specific phages in the area with a strong plague epidemic. Crucially, comparative genomics has been conducted to analyze the genetic changes in both the Y. pestis and phages over different periods, revealing the dynamic and evolving nature of their symbiosis. These are the critical steps to study the mechanism of the symbiosis.

Relationship Between Climate Change and Marmot Plague of Marmota himalayana Plague Focus - the Altun Mountains of the Qinghai-Xizang Plateau, China, 2000-2022.

Introduction: Plague is a zoonotic disease that occurs naturally in specific geographic areas. Climate change can influence the populations of the plague host or vector, leading to variations in the occurrence and epidemiology of plague in animals. Methods: In this study, we collected meteorological and plague epidemiological data from the Marmota himalayana plague focus in the Altun Mountains of the Qinghai-Xizang Plateau. The data spanned from 2000 to 2022. We describe the climatic factors and plague epidemic conditions and we describe their analysis by Pearson's correlation. Results: During the period from 2000 to 2022, the isolation rates of Yersinia pestis (Y.pestis) from marmots and fleas were 9.27% (451/4,864) and 7.17% (118/1,646), respectively. Additionally, we observed a positive rate of F1 antibody of 11.25% (443/3,937) in marmots and 18.16% (142/782) in dogs. With regards to climate, there was little variation, and a decreasing trend in blowing-sand days was observed. The temperature in the previous year showed a negative correlation with the Y. pestis isolation rate in marmots (r=-0.555, P=0.011) and the positive rate of F1 antibody in marmots (r=-0.552, P=0.012) in the current year. The average annual precipitation in the previous two years showed a positive correlation with marmot density (r=0.514, P=0.024), while blowing-sand days showed a negative correlation with marmot density (r=-0.701, P=0.001). Furthermore, the average annual precipitation in the previous three years showed a positive correlation with the isolation rate of Y. pestis from marmots (r=0.666, P=0.003), and blowing-sand days showed a negative correlation with marmot density (r=-0.597, P=0.009). Conclusions: The findings of this study indicate that there is a hysteresis effect of climate change on the prevalence of plague. Therefore, monitoring climate conditions can offer significant insights for implementing timely preventive and control measures to combat plague epidemics.