Habitat and Season Drive Chigger Mite Diversity and Abundance on Small Mammals in Peninsular Malaysia

Abstract

Chigger mites are vectors of the bacterial disease scrub typhus, caused by Orientia spp. The bacterium is vertically transmitted in the vector and horizontally transmitted to terrestrial vertebrates (primarily wild small mammals), with humans as incidental hosts. Previous studies have shown that the size of the chigger populations is correlated with the density of small mammals in scrub typhus-endemic regions. Here, we explore interactions between the small mammals and chiggers in two oil palm plantations located in the Perak and Johor states of Peninsular Malaysia. The location in Perak also contained an aboriginal (Orang Asli) settlement. A ~5% sub-sample from 40,736 chigger specimens was identified from five species of small mammals (n = 217), revealing 14 chigger species, including two new records for Malaysia. The abundance and species richness of chiggers were significantly affected by habitat type (highest in forest border), state (highest in Perak), and season (highest in dry). The overall prevalence of Orientia tsutsugamushi DNA in small-mammal tissues was 11.7% and was not significantly affected by host or habitat characteristics, but in Johor, was positively associated with infestation by Leptotrombidium arenicola. These findings highlight the risk of contracting scrub typhus in oil palm plantations and associated human settlements.

Molecular Surveillance for Vector-Borne Bacteria in Rodents and Tree Shrews of Peninsular Malaysia Oil Palm Plantations

“…Although the main ecotype covered in our study was the oil palm plantation, there were rice fields and residential areas near the Perak study site. Our previous ecological analysis of O. tsutsugamushi infection in the same rodents analyzed in the current study concluded that neither habitat nor season was significantly associated with infection, although infection prevalence was highest in oil palm plantations compared with peripheral habitats [ 64 ]. This lack of statistically significant ecological effects may be due to the long duration of O. tsutsugamushi infection in small mammals or high reinfection rates coupled with their movement between adjacent habitats [ 40 ].…”

“…This lack of statistically significant ecological effects may be due to the long duration of O. tsutsugamushi infection in small mammals or high reinfection rates coupled with their movement between adjacent habitats [ 40 ]. In Johor, the O. tsutsugamushi infection of small mammals was positively associated with a Malaysian endemic vector, Leptotrombidium arenicola , although no significant relationship between any chigger species and O. tsutsugamushi infection in Perak was apparent [ 64 ].…”

Multiplex PCR assay for identifying five species of chigger mites in the Republic of Korea

“…Chigger mites are an abnormal disease vector that parasitizes only in the larval stage; they progress through a life cycle including eggs, larvae, nymphs, and adults, only requiring animal tissue uid to grow from the larval stage into nymphs [10][11][12]. Chigger mites mainly inhabit humid and grassy environments, such as forests, grasslands, and shrubbery, and their spawning behavior is affected by humidity and temperature [8, 13,14].…”

Multiplex PCR assay for identifying five species of chigger mites in the Republic of Korea

“…Chigger mites are an abnormal disease vector that parasitizes only in the larval stage; they progress through a life cycle including eggs, larvae, nymphs, and adults, only requiring animal tissue fluid to grow from the larval stage into nymphs (Lerdthusnee et al 2002;Lee 2017;Alkathiry et al 2022). Chigger mites mainly inhabit humid and grassy environments, such as forests, grasslands and shrubbery, and their spawning behavior is affected by humidity and temperature (Van Peenen et al 1976;Chang 1995;Takahashi et al 1995).…”

“…2002; Lee 2017; Alkathiry et al . 2022). Chigger mites mainly inhabit humid and grassy environments, such as forests, grasslands and shrubbery, and their spawning behavior is affected by humidity and temperature (Van Peenen et al .…”