R. felis has been traditionally grouped as a member of the spotted fever group (SFG) rickettsia . It was first described in the cat flea, Ctenocephalides felis, in the United States . Since then, the pathogen has been detected in mosquitoes, fleas, ticks, mites and lice [3, 10, 17, 18]. To date, thirty-nine species of arthropods have been associated with R. felis . Ticks is considered one of the most important vectors of R. felis. Tick plays a key role in the epidemiology of zoonotic diseases, such as human granulocytic anaplasmosis. Previous studies showed that R. felis was found to infect H. longicornis in regions of Jiangsu, China, and to infect Leptotrombidium scutellare mites in Huangdao District of Qingdao City, China . The phenomenon may be attributed to the different vectors of R. felis in different ecological environments.
Anhui province located in the eastern part of China, it’s an offshore inland province between east longitude 114°54 '~ 119° and northern latitude 37°41 '29 ~ 34°38' roughly, and it can be roughly divided into five regions: Huaibei Plain, Jianghuai Hill, Western Dabie Mountainous Area, Wannan Mountainous Area and the Plain along the river. In this study, we collected all the H. longicornis ticks from the mountainous areas owing to almost no ticks in the plain areas. We detected R. felis from these ticks with nested PCR (or real-time PCR) based on 16S rRNA, 17kDa and orfB genes. As we all known, sequence comparison of the 16S rRNA gene is considered one of the most powerful and precise molecular methods for analyzing the phylogenetic relationships of bacteria. In this study, the 16S rRNA gene sequences of the positive tick samples from Anhui Province were closely related to R. felis (Fig.1). Additionally, differences in sequencing results indicate that there may be a few of genetic variants in Anhui Province, even simultaneously in the same region. As can be seen from Figure 1, the two 16S RNA sequences from Anhui Province were all identical to R. felis URRWXCal2 (CP000053.1). However, phylogenetic analysis of 17kDa protein gene indicated that R. felis strain Anhui-1 detected in ticks from Anhui Province, was more similar with R.felis isolates (MF491767.1 and AF195118.1), while R. felis strain Anhui-2 was more similar with these isolates (MF491774.1, MF491775.1 and MF491778.1), implying R. felis in China is genetically diverse (Fig. 2). For further confirmation, qPCR was carried out using specific R. felis primers targeting orfB gene to detect the positive samples. Through sequence analysis, all the positive samples were R. felis, and the nucleotide sequences of orfB from the ticks were identical to each other.
To our knowledge, this is the first report of R. felis in H. longicornis in Anhui Province of China. Their vectorial capacity should be further experimentally validated. Additionally, this study further supports the potential role of ticks as vectors of R. felis and suggests that this pathogen has a wide geographical distribution in China, including Anhui Province. Further studies are needed to evaluate the potential risk of humans to acquire R. felis infection and investigate the epidemiology (for example, in mosquitoes, lice and mice) and transmission mechanisms of R. felis, because there is no doubt that humans live in close association with R. felis-infected vectors throughout Anhui Province of China.