Seasonal dynamics and niches of three vector chigger species at a focus of scrub typhus in southwest China

TL;DR

This study examines the seasonal activity and host preferences of three chigger species in southwest China to better understand scrub typhus transmission.

Contribution

The study reveals distinct seasonal patterns and niche differences among three key vector chigger species in a scrub typhus focus.

Findings

Leptotrombidium deliense and L. imphalum show summer-autumn activity peaks, while L. scutellare peaks in autumn-winter.

L. deliense has the widest temporal niche, and L. scutellare has the widest host niche.

Temperature is a key driver of seasonal fluctuations in chigger populations.

Abstract

The present study aims to investigate the seasonal dynamics of main vectors of scrub typhus, and thereby provide scientific information for the surveillance and control of the disease.

A field investigation lasting for 12 consecutive months was conducted at a fixed survey site (Waxi Village) in Binchuan County (a focus of scrub typhus), Yunnan Province of southwest China between 2019 and 2020. Based on the taxonomic identification of all collected chigger mites, the three vector chigger species of scrub typhus (Leptotrombidium deliense, L. scutellare and L. imphalum) were screened out as the object of this study. The constituent ratio (Cr), prevalence (PM), mean abundance (MA), and mean intensity (MI) were calculated to reflect the mite infestation status. The Levins’ niche breadth (Bi) and Pianka’s proportional similarity ratio (Oij) were used to calculate the ecological niche breadth and niche overlap of chiggers on different host species and temporal series.

These three vector chigger species were the dominant mites at the survey site, accounting for 60.72% of the total 115 chigger species (Cr=60.72%, 132,160/217,671). In seasonal fluctuations, L. deliense showed two peaks in summer and autumn, and the highest peak was in August of summer with highest infestation indexes (Cr=44.29%, MA=322.48, MI=422.56) on the hosts. Leptotrombidium imphalum mainly appeared in summer and autumn, and peaked in September (Cr, MA and MI) and October (PM) of early autumn. Leptotrombidium scutellare mainly appeared in November, December and January, and peaked in November of late autumn (Cr=66.09%) and December of early winter (Cr=33.83%). Leptotrombidium deliense had the widest temporal niche (Bi=0.248) and L. scutellare had the widest host niche (Bi=0.268). Leptotrombidium deliense and L. imphalum had the highest temporal niche overlap (Oij=0.715) and host niche overlap (Oij=0.986). The monthly average temperature significantly affected the seasonal fluctuation of L. scutellare.

The three vector chigger species can parasitize a wide range of hosts with low host specificity, and their coexistence as the dominant mites at the survey site increases the potential risk of transmission and focus persistence of relevant mite-borne zoonoses. Leptotrombidium deliense and L. imphalum have similar seasonal distribution patterns (summer-autumn type) and host selection, and L. scutellare has a different type of seasonal fluctuation, autumn-winter type. The temporal and host niches of L. scutellare are very different from those of L. deliense and L. imphalum. The temperature is the most important climate factor that drives the seasonal dynamics of vector chiggers.

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