Table 2. The epidemiological characteristics of host (Merionesunguiculatus) and vector surveillance in the Inner Mongolian Autonomous Region from 1981 to 2019.

Item	The third stage (1981–1999)	The fourth stage (1999–2019)	Total (1981–2019)
Investigation area of M. unguiculatus (ha)	20,788.95	26,533.00	47,321.95
Density of M. Unguiculatus (/ha)	4.50	3.49	3.93
Nocturnal rodent capture rate (%)	4.55	3.43	3.98
Percentage of hosts infested with fleas (%)	23.04	27.83	25.56
The host-flea index	0.57	0.76	0.67
Percentage of the passage of burrows infested with nomadic fleas (%)	2.39	11.53	6.96
The index of nomadic fleas at the passage of burrows	0.09	0.24	0.16
Percentage of nests infested with fleas (%)	55.79	59.81	57.91
The nest-flea index	8.40	8.22	8.31
M. Unguiculatus positive rate (%)	1.15	0.55	0.87
Flea positive rate (%)	2.15	1.61	1.88
Indirect hemagglutination assay positive rate of M. unguiculatus (%)	1.39	0.42	1.06