Serological Epidemiological Investigation of Tibetan Sheep (Ovis aries) Plague in Qinghai, China

Abstract

The plague, which is caused by the Gram-negative coccobacillus bacterium Yersinia pestis, has been classified as a reemerging infectious disease by the World Health Organization. The Qinghai-Tibet Plateau natural plague focus is the largest plague focus in China, and Marmota himalayana is the primary host of the plague. Tibetan sheep (Ovis aries) were first identified as naturally infected hosts of Y. pestis based on etiological evidence in 1975, and activities such as slaughtering or skinning Tibetan sheep that have been infected by Y. pestis or died from Y. pestis infection had caused severe human plague in Qinghai. Tibetan sheep are important domestic livestock in the Qinghai-Tibet Plateau. Knowledge regarding the infection rate of Y. pestis in Tibetan sheep is important for understanding the range of infection and improving measures to control plague epidemics in this area. In this study, a serological survey involving 12,710 Tibetan sheep in all 44 counties in Qinghai Province was conducted. The total positive rate of indirect hemagglutination assay for Y. pestis in Tibetan sheep in Qinghai was 0.68% (86/12,710). Serological positivity to the Y. pestis F1 antibody was found in Tibetan sheep in all prefectures, except the Haidong and Haibei prefectures in Qinghai, with the seropositive rate in different counties ranging from 0.33% to 5.2% and the titers in the positive sera ranging from 1:20 to 1:5120. In addition, the seropositive rates in animal plague focus counties were higher than the rates in non-animal plague counties. Such results indicated a widespread infection of Tibetan sheep with Y. pestis in Qinghai, even though only sporadic epidemics of Tibetan sheep plague have been reported in Qinghai.

The complex genomic diversity of Yersinia pestis on the long‐term plague foci in Qinghai–Tibet plateau

“…It is the biggest and one of the most active areas of animal and human plague in China with a large variety of plague animals and strong virulence of plague bacteria (Ge et al, 2015;He et al, 2021;Wang et al, 2011). Moreover, in addition to the main host (marmot), the secondary hosts have appeared from time to time in recent years (Dai et al, 2018(Dai et al, , 2019Ge et al, 2015). The diversifying natural selection possibly coincides with the complex spatial epidemiology and genetic diversity of Y. pestis in Qinghai-Tibet.…”

Genetic source tracking of human plague cases in Inner Mongolia-Beijing, 2019

“…The diagnostic standards used in this plague outbreak included the identification of Y.pestis isolates by culture with a special phage lysis assay [9] or PCR positivity together with immunological methods positive for F1 antigen in clinical samples, i.e., reverse indirect haemagglutination assay (RIHA) and/or colloidal gold-immunochromatography assay positive. The serum samples collected from patients were tested for antibodies against the F1 antigen via indirect haemagglutination assay (IHA) [10]. The PCR method in this study was developed by members of our team in ICDC [11], including the caf1 gene and YPO0392 segment target, and the sensitivity and specificity of two targets of PCR were evaluated.…”

Spatiotemporal Variations of Plague Risk in the Tibetan Plateau from 1954–2016

“…And 96.8% of plague cases were caused by Himalayan marmot (main plague hosts in the TP). In this marmot plague foci, animal plague pandemics continuously and human plague outbreaks occur frequently [ 9 ]. According to statistics, more than 3502 Y. pestis were isolated between 1954 to 2020, among which 95.26% were from infected animal and vectors, 4.68% were from human and 0.06% were from soil.…”