Distribution and Characteristics of Human Plague Cases and Yersinia pestis Isolates from 4 Marmota Plague Foci, China, 1950-2019

Abstract

We analyzed epidemiologic characteristics and distribution of 1,067 human plague cases and 5,958 Yersinia pestis isolates collected from humans, host animals, and insect vectors during 1950-2019 in 4 Marmota plague foci in China. The case-fatality rate for plague in humans was 68.88%; the overall trend slowly decreased over time but fluctuated greatly. Most human cases (98.31%) and isolates (82.06%) identified from any source were from the Marmota himalayana plague focus. The tendency among human cases could be divided into 3 stages: 1950-1969, 1970-2003, and 2004-2019. The Marmota sibirica plague focus has not had identified human cases nor isolates since 1926. However, in the other 3 foci, Y. pestis continues to circulate among animal hosts; ecologic factors might affect local Y. pestis activity. Marmota plague foci are active in China, and the epidemic boundary is constantly expanding, posing a potential threat to domestic and global public health.

Keywords: China; Marmota; Yersinia pestis; bacteria; epidemiology; fleas; marmots; parasites; plague; public health; vector-borne infections; zoonoses.

Figure 1

Plague ecology and surveillance of Yersinia pestis in the Marmota himalayana plague focus, Qinghai-Tibet Plateau, China, 1950–2019. This focus area encompasses Qinghai Province, Gansu Province, Tibet Autonomous Region, Sichuan Province, and Xinjiang Uygur Autonomous Region. A) The Himalayan marmot (M. himalayana), the predominant marmot species in this focus. Photograph by Xin Wang. B) Number of Y. pestis isolates collected from humans, animal hosts, and insect vectors (mostly Callopsylla dolabris and Oropsylla silantiewi fleas) in the focus.

Figure 4

Frequency of human plague cases and case-fatality rates in 2 Marmota plague foci, China, 1950–2019. A) Marmota himalayana plague focus of the Qinghai-Tibet Plateau, which includes Qinghai Province, Gansu Province, Tibet Autonomous Region, Sichuan Province, and Xinjiang Uygur Autonomous Region. B) Marmota baibacina–Spermophilus undulatus plague focus includes Xinjiang Uygur Autonomous Region.

Figure 5

Number of Yersinia pestis isolates and human plague cases in Marmota plague foci, China, 1950–2019. Columns represent 5-year intervals. The 3 plague foci from which Y. pestis isolates have been collected are the Marmota himalayana plague focus of the Qinghai-Tibet Plateau, which includes Qinghai Province, Gansu Province, Tibet Autonomous Region, Sichuan Province, and Xinjiang Uygur Autonomous Region; the Marmota baibacina–Spermophilus undulatus plague focus of the Tianshan Mountains, Xinjiang Uygur Autonomous Region; and the Marmota caudata plague focus of the Pamir Plateau, Xinjiang Uygur Autonomous Region. A) Number of Y. pestis isolates collected from humans, animal hosts, and insect vectors. Lowercase letters at top indicate periods of isolate collection: a) early attempts during 1950–1959; b) increased diagnosis and animal plague surveillance increased number isolates collected during 1960–2009; and c) decrease in isolates likely due to decreasing numbers of dead marmot species found around active Y. pestis areas during 2010–2019. B) Number of human plague cases and case-fatality rates.

Figure 6

Human plague cases detected in 4 Marmota plague foci, China. A) 1950–1969; B) 1970–2003; C) 2004–2019. Dot size indicates the number of years during which plague occurred in each timeframe; dot colors indicates number of periods (A, B, C) during which plague occurred for each location. Blue shading indicates the Marmota himalayana plague focus; purple shading indicates the Marmota baibacina–Spermophilus undulatus plague focus; red shading indicates the Marmota caudata plague focus; and yellow shading indicates the Marmota sibirica plague focus.

Figure 2

Plague ecology and surveillance of Yersinia pestis in the Marmota baibacina–Spermophilus undulatus plague focus of the Tianshan Mountains, Xinjiang Uygur Autonomous Region, China, 1950–2019. A) The gray marmot (M. baibacina), the predominant marmot species in this focus. Photograph by Yujiang Zhang. The long-tailed ground squirrel (S. undulatus) also is an Y. pestis host in the focus. B) Number of Y. pestis isolates collected from humans, animal hosts, and insect vectors (mostly Oropsylla silantiewi and Citellophilus tesquorum fleas) in the focus.

Figure 3

Plague ecology and surveillance of Yersinia pestis in the Marmota caudata plague focus of the Pamir Plateau, Xinjiang Uygur Autonomous Region, China, 1950–2019. A) The red marmot (M. caudata), the predominant marmot species in this focus. Photograph by Yujiang Zhang. B) Number of Y. pestis isolates collected from humans, animal hosts, and insect vectors (mostly Oropsylla silantiewi fleas) in the focus.

Figure 7

Ecology and surveillance of marmots in the Marmota sibirica plague focus of the Hulun Buir Plateau, Inner Mongolia, 1950–2019. A) Tarbagan marmot (M. sibirica), the predominant marmot species in this focus. Photograph by Jun Liu. B) Average density of this species in the focus area. Tarbagan marmots host Oropsylla silantiewi fleas, a known vector of Yersinia pestis, but no Y. pestis isolate has been collected from humans, animal hosts, or insect vectors in this focus since 1926.