On November 11, 2019, Beijing Center for Disease Control (Beijing CDC) identified two cases of Yersinia pestis (Y. pestis)-induced pneumonic plague in a husband and wife from the Sunitezuo Qi (County) of the Xilinguole League (Prefecture) in Inner Mongolia Autonomous Region. Three days later on November 14, 2019, another case of Y. pestis was identified in a patient from Huade County of Ulanchabu City in Inner Mongolia, 130 kilometers from the first two cases. China CDC established no epidemiological relationship between the two events (Figure 1).Figure 1. Geographic distribution and relation of the three human plague cases in Inner Mongolia and Beijing. Part A: vertical line area: Meriones unguiculatus plague focus; horizontal line area: Microtus brandti focus; slant line area: Spermophilus Dauricus focus; cross line area: overlap area between Meriones unguiculatus and Spermophilus Dauricus. Part B: map of plague focus types in China.
A total of 447 persons with direct contact in Beijing and 46 in Inner Mongolia were quarantined for medical observation. As of November 21, 2019, all persons with direct contact were discharged from medical observation.
Human plague has been well controlled since 1959 in Inner Mongolia. During 1960-2018, only nine human plague cases with two deaths occurred in Inner Mongolia (5). The most recent human plague cases were reported from this focus in 2004, and as with Patient C, were due to skinning a dead hare (6).
There are four plague foci in Inner Mongolia (7). These are an M. unguiculatus plague focus in the Inner Mongolian Plateau, a Microtus brandti plague focus in the Xilin Gol Grassland, a Spermophilus Dauricus plague focus in the Song-Liao Plain and a Marmota sibirica plague focus in the Hulun Buir Plateau (a silent plague focus). The M. unguiculatus plague focus in Inner Mongolia can be divided into two parts - the Ordos plateaus and the desert steppe of the Ulanqab plateaus. The S. dauricus focus includes the Song-Liao plain hills and the dry steppe of Qahar area (5).
Combining previous plague epizootic data (5) and recent surveillance data, the Inner Mongolia animal plague epidemic can be divided into four phases, as illustrated in Table 1. The Inner Mongolia plateau focus of M. unguiculatus was first identified in 1954. The total area of this focus is 134,803 km2 and encompasses 22 counties (Qi) in the middle and western parts of Inner Mongolia (5). In the last 5 years, the Inner Mongolia natural foci of animal plague has been active. In 2019, virulent animal plague epidemics occurred in this focus, which has a high density of rats.
Phase Years Main host in epizootic Plague sub-focus † First epizootic 1954-1955 S. dauricus Qahar area (1985-1989) Second epizootic * 1969-1972 M. unguiculatus Ordos plateau, Ulanqab plateaus (1968-1969) S. dauricus Qahar area (1970) Third epizootic 1973-1998 M. unguiculatus Ordos plateau (1973-1976,1987-1990,1996) Ulanqab plateaus (1974,1979,1991)Baoto City (1982,1985) S. dauricus Song-Liao Plain (1985-1989) Qahar area (1973-1974, 1988-1994) Fourth epizootic 2001-2019 M. unguiculatus Ordos plateau (2015, 2016) Spread throughout all M. unguiculatus plague focus (2019) *Virulent animal plague epidemics occurred in the second phase. The epidemics swept all three foci of Inner Mongolia.
†Microtus brandti plague focus of the Xilin Gol Grassland was not included because the Y. pestis isolated in this focus was considered to have low pathogenicity to humans.
Table 1. Animal plague epidemics in Inner Mongolia in the last 70 years.
Since the founding of the People’s Republic of China, this is the first instance in which pneumonic plague was imported into a major city in China. Although clearly a transported case, awareness and appropriate measures should always be implemented. These three cases can provide important lessons for public health practitioners.