A novel Candidatus Rickettsia chiangmaiensis and occurrence of Candidatus Rickettsia laoensis in hard ticks from Chiang Mai Province, Thailand

Hard ticks are important vectors of zoonotic pathogens, including bacteria that cause rickettsiosis, Q fever, and anaplasmosis. In this study, 167 ticks were collected from vegetation in Chiang Mai Province, northern Thailand, and examined using morphological and molecular methods. Five tick species were identified: Dermacentor tamokensis (n = 81), D. bellulus (n = 49), D. pasteuri (n = 9), Ixodes acutitarsus (n = 26), and Haemaphysalis hystricis (n = 2), with the first three species newly characterized at the molecular level. Moreover, D. tamokensis and D. bellulus are newly recorded in Thailand. Phylogenetic analysis using the multilocus sequence analysis (MLSA) approach revealed two distinct genotypic groups of spotted fever group rickettsiae (SFGRs): a novel Candidatus Rickettsia chiangmaiensis in I. acutitarsus (20/26) and Candidatus Rickettsia laoensis in D. tamokensis (12/81) and D. bellulus (10/49). The latter SFGR was closely related to strains found only in western Thailand and Laos. Additionally, Coxiella-like endosymbionts (CLEs) were detected in D. tamokensis (61/81), D. bellulus (13/49), and H. hystricis (1/2), while Anaplasma sp. was found in D. tamokensis (2/81). Notably, double infections: Ca. R. laoensis-CLEs, Anaplasma-CLEs, and a triple infection: Ca. R. laoensis-CLE-Anaplasma were reported herein. These findings demonstrate the diverse bacterial associations in ticks, suggesting the ecological complexity of forested areas in northern Thailand.