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

Yan Lv¹Peng-Wu Yin¹Xian-Guo Guo^1,2*Rong Fan¹Cheng-Fu Zhao¹Zhi-Wei Zhang¹Ya-Fei Zhao¹Lei Zhang¹

• ¹Dali University Institute of Pathogens and Vectors, Yunnan, China
• ²Xian-Guo Guo, Dali, China

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), Dali Prefecture, Yunnan Province of southwest China between 2020 and 2021. Three vector chigger species (Leptotrombidium deliense, L. scutellare and L. imphalum) 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. Leptotrombidium imphalum mainly appeared in summer and autumn. Leptotrombidium scutellare mainly appeared in November, December and January, and peaked in November of late autumn and December of early winter. 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). A positive correlation existed between the humidity and infestation indexes of two vector chigger species, L. deliense (r: 0.727-0.807, P<0.05) and L. imphalum (r: 0.600-0.726, P<0.05). A negative correlation existed between the temperature and L. scutellare's infestation indexes with r= -0.666 for PM and r= -0.657 for MI (P<0.05). A positive correlation existed between infestation indexes of two vector chigger species (L. deliense and L. imphalum) and scrub typhus cases (P<0.05). In conclusion, the three vector chigger species can ectoparasitize 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 temperature and humidity may be important climate factors affecting the seasonal dynamics of vector chiggers. The seasonal fluctuations of vector chigger populations are associated with the seasonal incidence of scrub typhus.