Abundance and Infestation of Mites on Bower's White-Toothed Rat (Berylmys bowersi) in Southwest China

Abstract

Chiggers (chigger mites) and gamasid mites are two groups of ectoparasites on rodents, and they can be the vectors or potential vectors of scrub typhus and hemorrhagic fever with renal syndrome (HFRS), while Bower's white-toothed rat (Berylmys bowersi) can serve as the reservoir host of the diseases. Based on field investigations at 117 survey sites of southwest China, a total of 2512 mites were collected from 55 B. bowersi rats. Under a microscope, these mites were taxonomically identified as 56 distinct species, comprising 37 chigger mite species and 19 gamasid mite species. The mite infestation burdens on B. bowersi were heavy, with a high prevalence (P_M = 85.45%), mean abundance (MA = 45.67), and intensity (MI = 53.45). Of 56 mite species identified, 7 are vectors of scrub typhus and HFRS. Of the seven vector mite species, Leptotrombidium scutellare was one of dominant chigger species, with a higher infestation index on rats (P_M = 21.82%, MA = 7.76) than the other six vector mite species. The sex ratio of female gamasid mites was higher than that of males. The number and infestation of adult gamasid mites were higher than those of immature mites. The infestation indexes of mites on B. bowersi hosts varied with the host's sex and age and fluctuated along different environmental gradients. The association coefficient (V) showed a slight positive association between chiggers and gamasid mites, suggesting that these two groups of mites may coexist on B. bowersi rats. Spearman correlation coefficients showed positive correlations among some dominant and vector mite species, indicating that some mite species tend to select the same hosts. A total of 69 mite species (47 chigger mite species and 22 gamasid mite species) on B. bowersi were estimated by species rarefaction and extrapolation curves. In conclusion, Berylmys bowersi has a high susceptibility to mite infestation, and it has the potential to harbor abundant mites, with heavy mite burdens. The occurrence of vector mite species, especially L. scutellare (the dominant species), increases the potential risk of transmission and the focus persistence of scrub typhus and HFRS in southwest China.

Keywords: chigger mite; gamasid mite; infestation; rodent; southwest China.

Figure 1

Distribution of 117 survey sites in the five provincial regions of southwest China (2001–2024). Annotation: The hollow circles (○) represent 117 survey sites, and the solid circles (●) represent 10 positive sites where Bower’s white-toothed rats (Berylmys bowersi) were captured.

Figure 2

Visualized sunburst charts for the constituent ratios of different families and genera of chiggers (a) and gamasid mites (b) identified from B. bowersi rats in southwestern China (2001–2024).

Figure 3

Visualized hierarchical network diagrams for the constituent ratios (C_r) of different chigger species (a) and gamasid mite species (b) identified from B. bowersi rats in southwestern China (2001–2024). Annotation: The circle size represents the constituent ratio (C_r) of corresponding mites. The bigger the circle, the higher the C_r.

Figure 4

The prevalence (P_M), mean abundance (MA), and mean intensity (MI) of dominant and vector mites. Annotation: The mark “*” represents the vector and potential vector species of mites. Five dominant mite species: The standard deviation and confidence intervals are 30.81 and 2.74–10.33 for MA, and 61.90 and 14.90–47.03 for MI. Seven vector mite species: The standard deviation and confidence intervals are 13.09 and 0.60–3.16 for MA, and 43.04 and 8.67–39.46 for MI.

Figure 5

Infestation fluctuation of mites on B. bowersi along different altitude (a) and latitude (b) gradients in southwest China (2001–2024). Annotation: Altitude gradients (a): The standard deviation and confidence intervals are 78.33 and 27.58–68.36 for MA, and 82.33 and 32.85–78.30 for MI; Latitude gradients (b): The standard deviation and confidence intervals are 78.33 and 26.06–66.93 for MA, and 82.33 and 31.26–79.56 for MI.

Figure 6

The heat map of interspecific relationships among dominant and vector species of mites on B. bowersi in southwest China (2001–2024). Annotation: The mite species marked with “#” are the vector species, which can serve as the vectors or potential vectors of scrub typhus and HFRS [57,58,59,60,61,62,63,64].

Figure 7

Species rarefaction and extrapolation curves of chigger mites (a) and gamasid mites (b). Annotation: The solid line in the figure is a rarefaction curve representing the observed values, while the dashed line is the extrapolation curve representing the estimated values.