Introduction
Picornaviruses (family Picornaviridae ) are small, non-enveloped RNA viruses with single-stranded and positive-sense polarity. As of March 2020, 147 species divided into 63 genera have been known currently in the family Picornaviridae(https://www.picornaviridae.com/), many of which had been found to result in significant diseases in humans and a wide variety of animals. The genus Kobuvirus is a novel recognized member of the family Picornaviridae , which contains a genomic organization similar to that of other picornaviruses and has a linear genome ranging from 8.2 to 8.4 kb in length. The genome structure of Kobuvirus is composed of VPg, 5’ UTRIRES-V, a large open reading frame (ORF) encoding a leader protein (L) and other three functional regions (P1-P2-P3), 3’ UTR and poly (A) tail. The P1 gene region encodes the structural proteins (VP0-VP3-VP1), whereas P2 (2AH-Box/NC-2B-2C) and P3 (3A-3BVPg-3Cpro-3Dpol) gene regions encode non-structural proteins (Khamrin, Maneekarn, Okitsu, & Ushijima, 2014). Of these, the 3D region as the most conserved region plays an essential role in viral replication (Lescar & Canard, 2009), whereas the VP1 gene is the highly variable motif encoding the most important viral capsid protein that determines the pathogenicity and antigenicity for kobuvirus (Reuter, Boros, & Pankovics, 2011).
Since the determination of the first human kobuvirus (Achi virus, AiV) in a patient with nonbacterial diarrhea in March 1989, Japan (Yamashita, Sakae, Ishihara, Isomura, & Utagawa, 1993), the novel kobuvirus strains have been determined as members of the genus Kobuvirus from a variety of animal species. In 2003, bovine kobuvirus (BKV) as a cytopathic agent was first recognized in the culture medium of HeLa cells that had been used over 30 years in a laboratory in Japan (Yamashita et al., 2003). Porcine kobuvirus (PKoV) was initially discovered in 2008 from the fecal samples of domestic pigs in Hungary (Reuter, Boldizsár, Kiss, & Pankovics, 2008). Subsequently, ovine kobuvirus (OKV) that was found to be related to BKV was initially isolated from young, healthy and domestic sheep in Hungary in 2009 (Reuter, Boros, Pankovics, & Egyed, 2010). In the last ten years,Kobuviruses have been described worldwide from a wide range of hosts, including black goats in South Korean (Lee et al., 2012), rabbits in Hungary (Pankovics et al., 2016), dogs in South Korean and Africa (Oem, Choi, Lee, Lee, & Choi, 2014; Olarte-Castillo et al., 2015), cats in South Korean and China (Cho et al., 2014; Niu et al., 2019), ferrets in the Netherlands and Sweden (Smits et al., 2013), rats (You et al., 2020) and bats (Wu et al., 2016) in China, wolves (Melegari et al., 2018), red foxes (Di Martino et al., 2014) and roe deer (Di Martino et al., 2015) in Italy.
According to the International Committee on Taxonomy of Viruses (ICTV),Kobuviruses comprise six officially recognized species to date. The species Aichivirus A contains Achi virus (found in humans), canine kobuvirus, feline kobuvirus, murine kobuvirus and a kobuvirus found in sewage (Ng et al., 2012), whereas Aichivirus B consists of bovine kobuvirus (Yamashita et al., 2003), ferret kobuvirus (Smits et al., 2013) and ovine kobuvirus (Reuter et al., 2010). RegardingAichivirus C , two distinct types have been described, including porcine kobuvirus and caprine kobuvirus (Reuter, Boldizsár, & Pankovics, 2009), while cattle kobuvirus (Otomaru et al., 2016), rabbit (Pankovics et al., 2016) and bat kobu-like viruses representAichivirus D, E and F , respectively.
Murine kobuvirus (MuKV) belongs to a member of the speciesAichivirus A that initially detected from the stools of a canyon mouse (Peromyscus crinitus ) in the USA in 2010 (Phan et al., 2011). Subsequently, MuKVs were identified in Hungary (Reuter et al., 2011), Vietnam (Lu et al., 2018) and USA (Williams et al., 2018) from fecal samples of several rodent species, including striped field mouse (Apodemus agrarius ), Norway rat (Rattus norvegicus ),Rattus losea , Rattus argentiventer and Mus musculus . We have recently initially conducted an epidemiological study for rat kobuvirus in Rattus norvegicus from Guangdong, China (You et al., 2020). However, lack of information on kobuvirus in other murine rodent species in China; here, we investigate the prevalence and genetic characterization of MuKV in Rattus losea , Rattus tanezumiand Rattus norvegicus among several regions in Southern China.