Ecological and microbiological diversity of chigger mites, including vectors of scrub typhus, on small mammals across stratified habitats in Thailand
Chaisiri K., Gill A.C., Stekolnikov A.A., Hinjoy S., McGarry J.W., Darby A.C., Morand S., Makepeace B.L.
Animal Microbiome, 1: 18 (2019).
S U M M A R Y
Background: Scrub typhus, caused by a bacterial pathogen (Orientia spp.), is a potentially life-threatening febrile
illness widely distributed in the Asia-Pacific region and is emerging elsewhere. The infection is transmitted by the
larval stage of trombiculid mites (“chiggers”) that often exhibit low host specificity. Here, we present an analysis of
chigger ecology for 38 species sampled from 11 provinces of Thailand and microbiomes for eight widespread species.
Results: In total, > 16,000 individual chiggers were collected from 1574 small mammal specimens belonging to 18
species across four horizontally-stratified habitat types. Chigger species richness was positively associated with higher
latitudes, dry seasonal conditions, and host maturity; but negatively associated with increased human land use. Human
scrub typhus incidence was found to be positively correlated with chigger species richness. The bacterial microbiome
of chiggers was highly diverse, with Sphingobium, Mycobacterium, Neisseriaceae and various Bacillales representing the
most abundant taxa. Only Leptotrombidium deliense was found to be infected with Orientia and another potential
pathogen, Borrelia spp., was frequently detected in pools of this species. β-diversity, but not α-diversity, was
significantly different between chigger species and geographic regions, although not between habitat types.
Conclusion: Our study identified several key environmental and host-derived correlates of chigger species richness
across Thailand, which in turn impacted on human scrub typhus incidence. Moreover, this first extensive field survey of
the chigger microbiome revealed species- and province-level variation in microbial β-diversity across the country,
providing a framework for future studies on interactions between pathogens and other symbionts in these