Infestation and Distribution of Ascoschoengastia indica (a potential vector of scrub typhus) on Small Mammals in Yunnan Province, southwest China (2001-2022)

Background: This study aimed to reveal the infestation and distribution patterns of the chigger mite Ascoschoengastia indica (a potential vector of scrub typhus) on small mammals in Yunnan Province of southwest China, a focus of scrub typhus. Methods: Using field survey data from 34 investigation sites in Yunnan Province between 2001 and 2022, a retrospective analysis was conducted. Infestation indices, including constituent ratio (Cr), prevalence (PM), mean abundance (MA) and mean intensity (MI), were calculated. Levins’ index (B'i), Pianka’s index (Oij) and the association coefficient (V) were utilized to measure host niche breadth, host niche overlap and interspecific relationships. Result: A total of 4,848 A. indica were collected from 165 small mammals across 13 of the 34 sites. Overall infestation indices were PM = 3.17%, MA = 0.93 and MI = 29.38. The mites were predominantly concentrated in southern Yunnan, with Rattus tanezumi being the principal host (Cr = 92.49%). The abundance of A. indica exhibited biases associated with host sex and age and varied in different geographical landscapes, habitats and altitude gradients, with a distinct preference for low-altitudes. Ascoschoengastia indica had a substantial geographical and host overlap with another vector, Leptotrombidium deliense.