Plague Outbreak of a Marmota himalayana Family Emerging from Hibernation

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.

Characterization of Mu-Like Yersinia Phages Exhibiting Temperature Dependent Infection

Yersinia pestis is the etiological agent of plague. Marmota himalayana of the Qinghai-Tibetan plateau is the primary host of flea-borne Y. pestis. This study is the report of isolation of Mu-like bacteriophages of Y. pestis from M. himalayana. The isolation and characterization of four Mu-like phages of Y. pestis were reported, which were named as vB_YpM_3, vB_YpM_5, vB_YpM_6, and vB_YpM_23 according to their morphology. Comparative genome analysis revealed that vB_YpM_3, vB_YpM_5, vB_YpM_6, and vB_YpM_23 are phylogenetically closest to Escherichia coli phages Mu, D108 and Shigella flexneri phage SfMu. The role of LPS core structure of Y. pestis in the phages' receptor was pinpointed. All the phages exhibit "temperature dependent infection," which is independent of the growth temperature of the host bacteria and dependent of the temperature of phage infection. The phages lyse the host bacteria at 37°C, but enter the lysogenic cycle and become prophages in the chromosome of the host bacteria at 26°C. IMPORTANCE Mu-like bacteriophages of Y. pestis were isolated from M. himalayana of the Qinghai-Tibetan plateau in China. These bacteriophages have a unique temperature dependent life cycle, follow a lytic cycle at the temperature of warm-blooded mammals (37°С), and enter the lysogenic cycle at the temperature of its flea-vector (26°С). A switch from the lysogenic to the lytic cycle occurred when lysogenic bacteria were incubated from lower temperature to higher temperature (initially incubating at 26°C and shifting to 37°C). It is speculated that the temperature dependent lifestyle of bacteriophages may affect the population dynamics and pathogenicity of Y. pestis.

Brucella pleuritis misdiagnosed as tuberculous pleuritis: a case report

Pleurisy and pleural effusion caused by Brucella infection are rare. However, clinicians lack an understanding of these possibilities, and the underlying disorder is easy to misdiagnose. We report a 52-year-old male farmer who was admitted to hospital with a fever, chest pain, and shortness of breath. Closed chest drainage was performed by thoracocentesis, and the concentration of adenosine deaminase (ADA) in the pleural fluid was >45 U/L. Mononuclear cells in the pleural fluid accounted for 90% of the cells, and pathology indicated a large number of lymphocytes. The clinical diagnosis was tuberculosis with tuberculous pleurisy. However, subsequent pleural fluid culture results did not support tuberculous pleurisy. The results of pleural fluid culture indicated Brucella, and the results of Brucella tiger red plate agglutination indicated a titer of 1:400 (+++). The final diagnosis was brucellosis with pneumonia and pleurisy. After 12 weeks of oral treatment, the patient underwent follow-up chest radiographs. Radiography indicated complete resolution of the hydrothorax and pneumonia, and the patient reported no discomfort. The short-term curative effect was excellent. Pleurisy associated with brucellosis should be considered a differential for pleurisy in regions where brucellosis is endemic, to minimize the risk of misdiagnosis.