Distribution and infestation of Leptotrombidium scutellare (a major vector of scrub typhus) on small mammals across five provincial regions of Southwest China.

The chigger Leptotrombidium scutellare is a major vector of scrub typhus and a potential vector of hemorrhagic fever with renal syndrome (HFRS) in China. Between 2001 and 2022, a field survey was conducted at 114 survey sites in five provincial regions of southwest China, an important focus of scrub typhus and HFRS. A total of 20,254 L. scutellare were identified from 1,118 rodents and other sympatric small mammals (hosts) in 20 out of 114 survey sites, mainly concentrated in the middle longitude, latitude and altitude areas. The northwestern Yunnan (a tourist resort) was the main distribution area of L. scutellare. Most L. scutellare came from the mountainous landscape (C_r=82.73%) and outdoor habitat (C_r=99.21%). The hosts of L. scutellare crossed four orders, eight families, 19 genera and 33 species with low host specificity. More than half of L. scutellare mites (56.55%) came from the vole Eothenomys miletus with high infestation (P_M=17.99%, MA = 4.24, MI = 23.57). Leptotrombidium scutellare was of aggregated distribution among different individuals of its hosts, and it had sex and age bias of host selection with preference to male and adult hosts. The landscape, altitude, longitude, latitude and host were important factors influencing the distribution and infestation of L. scutellare. The occurrence of abundant L. scutellare with low host specificity in southwest China (especially in the tourist resort of northwestern Yunnan) would increase the risk of transmission and focus-persistence of scrub typhus and HFRS in the region.