Rickettsia japonica and Novel Rickettsia Species in Ticks, China

PCR amplification indicated the minimum infection rate of Rickettsia spp. was 0.66% in Haemaphysalis longicornis ticks collected from Shandong Province, China. Phylogenetic analysis based on the rrs, gltA, ompA, and ompB genes indicated that the ticks carried R. japonica, Candidatus Rickettsia longicornii, and a novel Rickettsia species related to R. canadensis.


The Study
We collected questing ticks by flagging during April-July 2013-2015. We collected them in Jiaonan County (35°35′-36°8′ N and 119°30′-120°11′E), Shandong Province, China. Jiaonan County is located on the Pacific coast of China and has a maritime monsoon-type climate. We identified tick species individually by morphology and confirmed by PCR amplification and DNA sequencing of the 16S rRNA gene of 2 nymphs and 2 adult ticks of each species as described previously (6,7).
For detection of Rickettsia DNA, we pooled ticks according to their developmental stages, with each pool consisting of 20 nymphs or 10 adult ticks. We homogenized them with Tissue Lyser II (QIAGEN, http://www. qiagen.com). We extracted total nucleic acids from the tick suspension using the AllPrep DNA/RNA Mini Kit (QIAGEN).
Initially, in all the tick pools, we amplified nucleic acid preparations with rickettsial universal primers targeting rrs, gltA, and ompB (B1-B4). We further amplified Rickettsia clones in the tick pools closely related to R. japonica with primers of ompA, an SFG rickettsia unique gene. The clones positive with rrs and gltA gene primers but negative with ompB primers (B1-B4) we further amplified with primers Cand-1 to Cand-4, which were designed from the R. canadensis ompB gene because the Rickettsia clones from these tick pools were closely related to R. canadensis on the basis of the rrs and gltA gene sequences (Table). We used distilled water as a negative control in each run.

Rickettsia japonica and Novel Rickettsia Species in Ticks, China
Author We collected a total of 2,560 H. longicornis ticks, 2,080 nymphs and 480 adults. PCR amplification indicated that 14 tick pools were positive with rrs, gltA, and ompB (B1-B4) primers and further positively amplified by PCR with ompA primers. In addition, 3 clones were positive with rrs, gltA, and ompB (Cand-1 to Cand-4) primers. The minimum infection rate of Rickettsia in the ticks was 0.66% (17/2,560), assuming 1 tick was positive in each positive pool of ticks.
Sequence analysis indicated that 3 clones (J84, J85, and J217) detected from the tick pools were closely related to R. Phylogenetic analysis based on the concatenated sequences of rrs, gltA, ompB, and ompA showed that Rickettsia clones (J84, J85, and J217) were clustered in the same clade with, but distinct from, R. canadensis; clone J244 was in the same clade as Candidatus Rickettsia longicornii; the remaining 13 clones were in the same clade as R. japonica. These results indicated that clones J84, J85, and J217 were a novel Rickettsia species; clone 244 was Candidatus Rickettsia longicornii; and other clones were R. japonica (Figure).

Conclusions
In this study, we demonstrated that H. longicornis ticks from China were infected with multiple Rickettsia species, including R. japonica, Candidatus Rickettsia longicornii, and a novel Rickettsia species. We named the novel species Candidatus Rickettsia jiaonani after the sampling site. The exact classification of Candidatus Rickettsia jiaonani needs to be further studied by sequencing the whole genomes of the organisms.
R. japonica infection in humans has been reported recently in Anhui Province in central China (11), suggesting that R. japonica is widely distributed in China and its epidemiology needs to be further investigated. Candidatus Rickettsia longicornii was previously detected in H. longicornis ticks collected from South Korea (12). Candidatus Rickettsia jiaonani is closely related to R. canadensis, which was first isolated from H. leporispalustris ticks removed from rabbits in Ontario, Canada, in 1963 and then from a H. leporispalustris tick removed from a black-tailed jackrabbit in California in 1980 (13).
H. longicornis ticks are native to East Asia, including China, Korea, and Japan, and they were introduced into Oceania, including Australia, New Zealand, Fiji, and Hawaii, through cattle importation (6). Recently, this tick species was found in 8 states in the eastern United States (14). This study and previous studies demonstrated that H. longicornis ticks carry R. japonica, Candidatus Rickettsia longicornii, Candidatus Rickettsia jiaonani, Anaplasma phagocytophilum, Ehrlichia, and severe fever with thrombocytopenia syndrome virus (12,15). These pathogens need to be monitored in countries in East Asia in which the H. longicornis tick is native and in the countries that this tick species has invaded.