Infestation, Community Structure, and Seasonal Dynamics of Chiggers on Small Mammals at a Focus of Scrub Typhus in Northern Yunnan, Southwest China

Chiggers are common ectoparasites and the exclusive vector of scrub typhus. From November 2020 to October 2021, a 12-month investigation was conducted at Waxi Village of Binchuan County, Yunnan Province of southwest China, a focus of scrub typhus. A total of 217,671 chiggers collected from 1329 small mammal hosts (belonging to 18 species) at the survey site were taxonomically identified as 115 species and 13 genera in the family Trombiculidae with high species diversity. Among the 115 chigger species identified, there were nine vector species. The prevalence (<i>P_M</i> = 69.38%), mean abundance (<i>MA</i> = 163.79 mites/per examined host), and mean intensity (<i>MI</i> = 236.09 mites/per infested host) were high. Three rodent species, <i>Rattus andamanensis</i>, <i>Apodemus chevrieri</i>, and <i>Mus caroli</i>, were the dominant hosts. Three vector chiggers, <i>L. deliense</i>, <i>L. scutellare,</i> and <i>L. imphalum</i>, were the dominant chiggers, with a constituent ratio (<i>C_r</i>) of 60.72%. The indexes of chigger infestation and community showed varying degrees of monthly and seasonal fluctuations. From August (summer) to September and October (autumn), the Margalef richness index (<i>R</i>), Shannon-Wiener diversity index (<i>H</i>), and Pielou evenness (<i>E</i>) of chiggers were at low levels, but the Simpson dominance index (<i>D</i>) was at a high level. The <i>C_r</i> and infestation indexes (<i>MA</i>, <i>MI</i>) of chiggers were high from August to October in summer and autumn, with abundant vector chiggers (such as <i>L. deliense</i> and <i>L. imphalum</i>) appearing in these seasons. The species richness of chigger community was highest in winter, but lowest in summer. The similarity of the chigger community was very high between August (summer) and September to October (autumn). The evenness of the chigger community was highest in spring and lowest in summer. In conclusion, small mammals are susceptible to chigger infestation with coexistence of multiple vector chigger species. Most chigger species have a wide range of hosts with low host specificity. The abundant vector chiggers (especially <i>L. deliense</i> and <i>L. imphalum</i>) in summer and autumn suggests that the surveillance campaign of scrub typhus and vector chiggers should mainly focus on these two seasons at the survey site.