INTRODUCTION
Ticks are obligate haematophagous ectoparasites of wild and domestic animals as well as humans, and there are approximately 900 tick species worldwide, of which many can transmit pathogenic agents, including viruses, bacteria, and protozoa (Mansfield, Jizhou, Phipps, & Johnson, 2017). Several tick-borne viruses (TBVs) are associated with serious diseases in humans and animals, such as tick-borne encephalitis virus (TBEV), Crimean-Congo hemorrhagic fever virus (CCHFV) and Nairobi sheep disease virus (NSDV) (Madison-Antenucci, Kramer, Gebhardt, & Kauffman, 2020). In recent decades, the incidence and geographical distribution of tick-borne viruses have an increasing tendency, highlighting the public health importance of these arboviruses (Medlock et al., 2013). Due to the application of next generation sequencing (NGS) in recent years, many novel viruses have been identified in different tick species of different regions worldwide (Brinkmann et al., 2018; Damian, Maghembe, Damas, Wensman, & Berg, 2020; Harvey et al., 2019; Souza et al., 2018). To our knowledge, the known identified TBVs include hundreds of viral members of at least 12 genera in 9 families of two orders as well as other unassigned members (J. Shi, Hu, Deng, & Shen, 2018).
In China, tick-borne encephalitis virus (TBEV) in theFlaviviridae family and Crimean-Congo hemorrhagic fever virus (CCHFV) in the Nairoviridae family are the two causative agents of viral encephalitis and hemorrhagic fever in northeastern and northwestern regions, respectively, that are transmitted by different tick species (X. Li et al., 2022; Moming et al., 2018; Xia et al., 2011). Emerging TBVs, such as severe fever with thrombocytopenia virus (SFTSV), Jingmen tick virus (JMTV), Alongshan virus (ALSV), Songling virus (SGLV), Beiji nairovirus (BJNV), Tacheng tick virus 1 and 2, have been reported to be associated with human diseases (Dong et al., 2021; Jia et al., 2019; Kobayashi et al., 2021; Q. Liu, He, Huang, Wei, & Zhu, 2014; X. Liu et al., 2020; Y. C. Wang et al., 2021; Z. D. Wang et al., 2019). Nairobi sheep disease virus (NSDV), another member in theNairoviridae family that can cause an acute hemorrhagic gastroenteritis in sheep and goats, has also been detected in ticks in China (Gong et al., 2015; L. Yang et al., 2019). Therefore, it is necessary to conduct routine surveillance of tick-borne viruses. The tick viromes have been analyzed in several provinces, including Heilongjiang, Liaoning, Hebei, Henan, and Yunnan in China (Meng et al., 2019; J. Shi, Shen, Wu, Zhang, & Deng, 2021; Xu et al., 2021; Z. Yang et al., 2021; Zhao et al., 2020), revealing a large number of novel RNA viruses of vertebrate and invertebrate hosts. These studies also suggest that the viromes are significantly affected by the tick species and geographical location.
The northeastern region has the richest forest resources in China, mainly concentrated in the Daxing’an mountain (DXAM), Xiaoxing’an mountain (XXAM) and Changbai mountain (CBM), resulting in abundant tick populations. In addition to TBEV, several emerging tick-borne viruses that may infect humans have been discovered in northeastern China, such as ALSV (Z. D. Wang et al., 2019), SGLV (Ma et al., 2021), BJNV (Y. C. Wang et al., 2021), and JMTV (Jia et al., 2019). Here, using metagenomic analysis, we found extensive diversity of RNA viruses in ticks in northeastern China, revealing potential public threats from the emerging TBVs. Further studies are needed to explain the natural circulation and pathogenicity of these viruses.