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

## TL;DR

This study analyzed chigger infestation on small mammals in northern Yunnan, China, revealing high diversity and seasonal patterns that could help improve scrub typhus surveillance.

## Contribution

The study provides detailed seasonal and community dynamics of chiggers in a scrub typhus endemic region, emphasizing key vector species and host interactions.

## Key findings

- Chiggers showed high species diversity with nine vector species identified, including L. deliense and L. imphalum.
- Chigger infestation was highest in summer and autumn, with low host specificity and high infestation rates.
- Vector chiggers were most abundant during these seasons, suggesting targeted surveillance is needed.

## Abstract

Being a common group of ectoparasites of rodents and other small mammals, chiggers (chigger mites) are the exclusive vector of scrub typhus and can also serve as potential vectors of hemorrhagic fever with renal syndrome (HFRS). From November 2020 to October 2021, a 12-month investigation was conducted to illustrate the infestation, community structure and seasonal dynamics of chiggers on small mammals at a focus of scrub typhus in northern Yunnan, southwest China. A total of 217,671 chiggers collected from 1329 small mammal hosts at the survey site (Waxi Village) were taxonomically identified as 115 species and 13 genera in the family Trombiculidae, with high species diversity. Rodents and other sympatric small animals at Waxi Village were susceptible to chigger infestation, with high infestation burdens, and coexistence of multiple vector chiggers. Most chigger species had a wide range of hosts with low host specificity. The chigger community showed a high similarity between August and October in summer and autumn with low species diversity, and a large number of vector chiggers, such as Leptotrombidium deliense and L. imphalum, appeared in these seasons.

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 (PM = 69.38%), mean abundance (MA = 163.79 mites/per examined host), and mean intensity (MI = 236.09 mites/per infested host) were high. Three rodent species, Rattus andamanensis, Apodemus chevrieri, and Mus caroli, were the dominant hosts. Three vector chiggers, L. deliense, L. scutellare, and L. imphalum, were the dominant chiggers, with a constituent ratio (Cr) 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 (R), Shannon–Wiener diversity index (H), and Pielou evenness (E) of chiggers were at low levels, but the Simpson dominance index (D) was at a high level. The Cr and infestation indexes (MA, MI) of chiggers were high from August to October in summer and autumn, with abundant vector chiggers (such as L. deliense and L. imphalum) 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 L. deliense and L. imphalum) 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.