Phylogenetic studies of bacteria (Rickettsia, Coxiella, and Anaplasma) in Amblyomma and Dermacentor ticks in Thailand and their co-infection

In this study, we attempted to detect Rickettsia, Coxiella and Anaplasma bacteria in one hundred and fourteen-Dermacentor and thirty three-Amblyomma unfed adult ticks that were collected from under leaves along animal trails at different places across Thailand. PCR amplification was used to identify bacterial infection with general conserved sequences of bacteria. The results revealed single infection in Amblyomma testudinarium ticks with Rickettsia (24%) and Coxiella (6%). Anaplasma bacteria were often detected in Dermacentor auratus ticks (32%). Coxiella spp. were detected in Dermacentor atrosignatus (6%) and D. auratus ticks (3%) in this study. Moreover, we found co-infection by Coxiella and Rickettsia bacteria (39%) in Am. testudinarium. In contrast, D. atrosignatus ticks were co-infected with Coxiella and Anaplasma bacteria (3%) and Dermacentor compactus ticks were co-infected with Rickettsia and Anaplasma spp. (25%). Interestingly, Am. testudinarium ticks (12%) were found for the first time to exhibit triple infection by these three bacteria. Phylogenetic studies showed the rickettsiae from ticks causing both single and multiple infections had sequence similarity with spotted fever group rickettsial strains, including Rickettsia massilliae, R. raoultii and R. tamurae. In addition, the phylogenetic analysis of the 16S rRNA gene of Coxiella bacteria showed that they were closely grouped with Coxiella endosymbionts in both Dermacentor and Amblyomma. Moreover, the Anaplasma identified in a D. auratus tick was grouped in the same clade with the pathogenic bacterium Anaplasma phagocytophilum. Bacterial co-infections in Dermacentor and Amblyomma ticks may cause co-transmission of some tick-borne microorganisms (pathogen and endosymbiont, whether enhance or reduce) in humans and animals and they could affect medical and veterinary health.