iSeq100 for metagenomic pathogen screening in ticks

Background: Ticks are blood sucking ectoparasites that play a pivotal role in the transmission of various pathogens to humans and animals. In Korea, Haemaphysalis longicornis is the predominant tick species and is recognized as the vector of pathogens causing various diseases such as babesiosis, borreliosis, rickettsiosis, and severe fever with thrombocytopenia syndrome. Methods: In this study, we developed a method to screen bacterial pathogens in H. longicornis using targeted high-throughput sequencing of the 16S rRNA V4 region using the state-of-the-art sequencing instrument, iSeq 100, and compared the findings with those of conventional PCR with specific primers. Results: Rickettsia spp. were detected in 18 out of 39 samples using iSeq 100 but in only 14 samples using conventional PCR. In the phylogenetic analysis using gltA and ompA sequences of the detected Rickettsia , the highest sequence similarity was found with Candidatus Rickettsia jingxinensis isolate Xian-Hl-79, Ca. R. jingxinensis isolate F18, and Ca. R. longicornii isolate ROK-HL727. In the microbiome study, Coxiella AB001519, a known tick symbiont, was detected in all 39 tick samples. The Actinomycetospora chiangmaiensis group was more abundant in Rickettsia spp.-positive samples than in Rickettsia spp.-negative samples. Conclusions: Thus, we demonstrated that iSeq100 can rapidly and economically screen potential pathogens in ticks and can be applied to large-scale pathogen screening in arthropods for vector-borne disease control programs.