From black plates to backyard animals: Chigger communities associated with wild and domestic hosts and the environment in a rural village setting

Chigger mites (larval Trombiculidae) are obligate ectoparasites, some species transmit Orientia tsutsugamushi , the causative agent of scrub typhus. Despite their public health significance in rural Southeast Asia, relationships between chiggers infesting wildlife, domestic animals and those present in the surrounding environment remain poorly characterised. We hypothesised that agricultural–forest ecotones would support higher chigger occurrence and that murid rodents would be the principal maintenance hosts of chigger communities. We conducted ecological observations of chigger communities associated with backyard chickens (n = 117), free-roaming dogs (n = 22), murid rodents (n = 96), insectivorous bats (n = 24) and environmental black-plate samples (n = 150) within a scrub typhus-endemic rural village in Nan Province, northern Thailand. Host-chigger associations were characterized using bipartite and unipartite network analyses. Twenty-one chigger species were identified, including four previously known to harbour O. tsutsugamushi: Ascoschoengastia indica, Leptotrombidium imphalum, Eutrombicula wichmanni and Walchia kritochaeta. Unfed questing chiggers occurred within the central residential area rather than being restricted to peripheral agricultural-forest interfaces as hypothesised. Murid rodents contributed the greatest chigger diversity, while backyard chickens exhibited unexpectedly high infestation prevalence (54.7%) and mean abundance. Environmental chigger detection rate was 11.3%. Eutrombicula wichmanni was recorded on free-roaming dogs, representing the first documented chigger infestation on dogs in Thailand, and a complete mitogenome was obtained from environmentally collected adults. Network analysis identified distinct rodent- and domestic animal-associated chigger communities, with the environmental chiggers linking both groups, whereas bat-associated chiggers were clearly isolated. These findings reveal complex chigger community structures with distinct ecological partitioning, highlighting the importance of domestic animals, particularly backyard chickens and free-roaming dogs (in addition to rodents) as critical components of peri-domestic transmission cycles. Future studies integrating host-chigger ecology with rickettsial pathogen screening would inform targeted disease surveillance and control programmes in rural endemic communities.