No evidence for persistent natural plague reservoirs in historical and modern Europe.

Caused by Yersinia pestis, plague ravaged the world through three known pandemics: the First or the Justinianic (6th-8th century); the Second (beginning with the Black Death during c.1338-1353 and lasting until the 19th century); and the Third (which became global in 1894). It is debatable whether Y. pestis persisted in European wildlife reservoirs or was repeatedly introduced from outside Europe (as covered by European Union and the British Isles). Here, we analyze environmental data (soil characteristics and climate) from active Chinese plague reservoirs to assess whether such environmental conditions in Europe had ever supported "natural plague reservoirs". We have used new statistical methods which are validated through predicting the presence of modern plague reservoirs in the western United States. We find no support for persistent natural plague reservoirs in either historical or modern Europe. Two factors make Europe unfavorable for long-term plague reservoirs: 1) Soil texture and biochemistry and 2) low rodent diversity. By comparing rodent communities in Europe with those in China and the United States, we conclude that a lack of suitable host species might be the main reason for the absence of plague reservoirs in Europe today. These findings support the hypothesis that long-term plague reservoirs did not exist in Europe and therefore question the importance of wildlife rodent species as the primary plague hosts in Europe.

Human Plague Case Diagnosed in Ningxia Tracked to Animal Reservoirs - Inner Mongolia Autonomous Region, China, 2021.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: There were a total of 4 and 3 human plague cases that occurred in the Inner Mongolia Autonomous Region in 2019 and 2020, respectively, with 1 and 2 deaths in 2019 and 2020 respectively, which indicated that plague still poses a significant threat to human health especially for farmers, shepherds, or residents living in native plague foci. WHAT IS ADDED BY THIS REPORT?: On August 14, 2021, 1 patient from the Otog Qi (County) in the Inner Mongolia sought treatment in Yinchuan City (the capital of Ningxia Hui Autonomous Region), where the patient was diagnosed with bubonic plague and secondary septicemic plague. The genetic source tracking of associated Yersinia pestis strains indicated that human plague cases were infected from animal reservoirs in Inner Mongolia. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: Major threats of plague to residents living in native plague foci are the infection by bites of bacterium-bearing fleas or direct contact with diseased or dead plague-infected animals. And the ability of early diagnostic is very critical for county-level hospital in native plague foci.

[Application of Best Subsets Regression on the risk classification for Spermophilus Dauricus Focus].

OBJECTIVE: To study the risk classification of animal plague in Spermophilus Dauricus Focus, using the Best Subsets Regression (BSR) model. METHODS: Matlab, BSR and exponential smoothing were employed to develop and evaluate a model for risk classification as well as to forecast plague epidemics at the Spermophilus Dauricus Focus. Data was based upon the Inner Mongolia surveillance programs. This model involved 7 risk factors, including density of Spermophilus dauricus, percentage of hosts infested, host flea index, percentage of nests infested, nest flea index, percentage of runways infested, and runway flea index. RESULTS: Forecasting values of the classification model(CM)were calculated and grouped into 3 risk levels. Values that over 2/3 of the CM would indicate the existence of potential epidemics while those below 1/3 would indicate that there were no risk for epidemics but when values that were in between would indicate that there exist for high risk. Annually, during the observation period in the Inner Mongolia Spermophilus Dauricus Foci, the detection of Yersinia pestis gave a risk rating value of 1 which stood for existing epidemics, while nil detection rate generated a 'zero' value which representing the situation of non-epidemic. The overall plague epidemics forecasting surveillance programs in 2012 at the Spermophilus Dauricus Foci indicated that no active plague was observed. When the forecasting values became over 2/3, combinations of all the risk factors would achieve the consistency rates of 100%. When the forecasting values were below 1/3, combinations of at least the first 4 factors could also achieve the consistency rates of 100%. However, when the forecasting values fell in between, combinations of at least the first 4 factors would achieve the consistency rates of around 50%. CONCLUSION: Results from our study showed that plague would not be active to become epidemic, in 2012.