Identification and characterization of recent retrovirus in Rhinolophus ferrumequinum bats

An investigation into retrovirus was conducted in six species of bats (Myotis aurascens, Myotis petax, Myotis macrodactylus, Miniopterus fuliginosus, Rhinolophus ferrumequinum, and Pipistrellus abramus) inhabiting South Korea. Exogenous retroviruses (XRVs) were detected in the tissue samples of R. ferrumequinum individuals by PCR assay. Proviruses were identified in all tissue samples through viral quantification using a digital PCR assay per organ (lung, intestine, heart, brain, wing, kidney, and liver), with viral loads varying greatly between each organ. In phylogenetic analysis based on the whole genome, the Korean bat retroviruses and the R. ferrumequinum retrovirus (RfRV) strain formed a new clade distinct from the Gammaretrovirus clade. The phylogenetic results determined these viruses to be RfRV-like viruses. In the Simplot comparison, Korean RfRV-like viruses exhibited relatively strong fluctuated patterns in the latter part of the envelope gene area compared to other gene areas. Several point mutations within this region (6,878-7,774 bp) of these viruses were observed compared to the RfRV sequence. One Korean RfRV-like virus (named Y4b strain) was successfully recovered in the Raw 264.7 cell line, and virus particles replicated in the cells were confirmed by transmission electron microscopy. RfRVs (or RfRV-like viruses) have been spreading since their first discovery in 2012, and the Korean RfRV-like viruses were assumed to be XRVs that evolved from RfRV.IMPORTANCER. ferrumequinum retrovirus (RfRV)-like viruses were identified in greater horseshoe bats in South Korea. These RfRV-like viruses were considered exogenous retroviruses (XRVs) that emerged from RfRV. Varying amounts of provirus detected in different organs suggest ongoing viral activity, replication, and de novo integration in certain organs. Additionally, the successful recovery of the virus in the Raw 264.7 cell line provides strong evidence supporting their status as XRVs. These viruses have now been identified in South Korea and, more recently, in Kenya since RfRV was discovered in China in 2012, indicating that RfRVs (or RfRV-like viruses) have spread worldwide.