Molecular Identification of Rickettsia Species in Haemaphysalis Ticks Collected from Southwest China

Rickettsia species are obligate intracellular Gram-negative bacteria that can infect a wide range of vertebrate hosts, including humans, through arthropod vectors such as Ixodid ticks. These ticks are a threat to humans and animals because they are the primary vectors or reservoirs for rickettsiae, which is of public health importance. In this study, we report the identification and percent of positive of Rickettsia spp. in ticks collected from Cangxi County, Southwest China. Haemaphysalis longicornis comprised 48.4% of the 188 ticks collected followed by Haemaphysalis flava (29.3%), H. doenitzi (12.2%), and Haemaphysalis hystricis (10.1%). A total of 63 (33.5%) ticks were positive with Rickettsia spp., with 48 (57%) of those being H. longicornis and 15 (27.3%) being H. flava. The other two tick species, however, did not have any ticks positive for rickettsial DNA. In addition, two different Rickettsia spp. were identified using gltA and ompA as molecular markers. The sequence of Rickettsia sp. infecting H. longicornis ticks was found to be identical to the Rickettsia sequences from Northeastern China and Japan (KF728367, AB516964). Phylogenetic analyses using these molecular markers support the notion that Rickettsia species from H. flava is the most close to a member of the Candidatus Rickettsia gannanii subgroup. The high percentage of Rickettsia positive in this Southwest China region suggests potential public health threat in the future and warrants to be monitored.