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Status and analysis of undetected plague cases in Yunnan Province, China
Chao Su1,2, Biao Duan2, Qun Duan1
1National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, 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.
Insights
Undetected plague cases were found in a Rattus flavipectus focus, suggesting human infections are underestimated. This highlights the need for improved plague surveillance and control in endemic areas.
Area of Science:
- Epidemiology
- Infectious Diseases
- Zoonotic Diseases
Background:
- The virulence of Yersinia pestis in Rattus flavipectus plague foci is generally low.
- Sporadic, undetected plague cases can occur even in areas with low bacterial virulence.
- Understanding these undetected cases is crucial for effective plague prevention and control strategies.
Purpose of the Study:
- To investigate and identify undetected, sporadic plague cases within a Rattus flavipectus plague focus.
- To provide a scientific basis for enhancing plague prevention and control measures.
- To assess the extent of Yersinia pestis transmission in the study area.
Main Methods:
- Conducted an epidemiological investigation and laboratory testing following a confirmed plague case in Yunnan Province, 2020.
- Performed an expanded survey within a 7-km radius, including human populations, domesticated dogs, and rats.
- Utilized Polymerase Chain Reaction (PCR) and indirect hemagglutination tests for sample analysis.
Main Results:
- Yersinia pestis was isolated from 100% of dead rats and 4% of live rats.
- 5% of domesticated dogs tested positive for F1 antibodies.
- A recent human plague infection rate of 0.92% was detected, with case locations aligning with animal Yersinia pestis hotspots.
Conclusions:
- Plague cases missed by routine surveillance exist in Rattus flavipectus foci.
- The actual prevalence of human plague infection may be significantly underestimated.
- Findings underscore the importance of integrated surveillance of animal and human populations for accurate plague assessment.
