Infection of Rodents by Orientia tsutsugamushi, the Agent of Scrub Typhus in Relation to Land Use in Thailand.

Kittipong Chaisiri,Jean-François Cosson,Serge Morand

doi:10.3390/tropicalmed2040053

Abstract

The relationship between land use structures and occurrence of the scrub typhus agent, Orientia tsutsugamushi, in small wild mammals was investigated in three provinces of Thailand: Buriram, Loei, and Nan. O. tsutsugamushi detection was performed using 16S ribosomal DNA (rDNA) amplicon sequencing approach using Miseq Illumina platform. In total, 387 animals (rodents and shrews) were examined for the infection. The 16S rDNA sequences of the bacterium were found in nine animals, namely Bandicota savilei, Berylmys bowersi, Leopoldamys edwardsi, Rattus exulans, R. tanezumi, and Rattus sp. phylogenetic clade 3, yielding 2.3% infection rate, with two new rodent species found infected by the bacterium in Thailand: B. bowersi and L. edwardsi. Using a generalized linear mixed model (GLMM) and Random Forest analyses for investigating the association between human-land use and occurrence of the bacterium, forest habitat appeared as a strong explicative variable of rodent infection, meaning that O. tsutsugamushi-infected animals were more likely found in forest-covered habitats. In terms of public health implementation, our results suggest that heterogenous forested areas including forest-converted agricultural land, reforestation areas, or fallows, are potential habitats for O. tsutsugamushi transmission. Further understanding of population dynamics of the vectors and their hosts in these habitats could be beneficial for the prevention of this neglected zoonotic disease.

Highlights

The obligate intracellular bacterium Orientia tsutsugamushi (Rickettsiales: Rickettsiaceae) is the causative agent of scrub typhus in humans, mainly reported in the Asia-Pacific region, and sporadically in some other regions of the world [1,2]
The 16S ribosomal DNA (rDNA) sequences of O. tsutsugamushi were found in only nine rodent individuals, i.e., B. savilei (2), B. bowersi (1), L. edwardsi (1), R. exulans (1), R. tanezumi (2), and Rattus sp. clade 3 (2) (Table 1)
Two rodent species were newly recorded in Thailand for infection by the bacterium: B. bowersi and L. edwardsi

Summary

Introduction

The obligate intracellular bacterium Orientia tsutsugamushi (Rickettsiales: Rickettsiaceae) is the causative agent of scrub typhus in humans, mainly reported in the Asia-Pacific region, and sporadically in some other regions of the world [1,2]. Chigger species from the genus Leptotrombidium are the main vectors of scrub typhus in Asia [9,10]. In terms of vertebrate hosts apart from humans, small terrestrial mammals such as rodents (rats, mice and ground squirrels), insectivores and tree-shrews have been reported as hosts of Leptotrombidium and are infected by the bacterium. They play important roles in the ecology of chigger mites and for the epidemiology of the disease [12,13]. It was hypothesized that their feeding activity on a wide range of hosts may explain the huge diversification of strains of O. tsutsugamushi [9,13]

Methods

Results

Conclusion