1. Mechanisms of XRV and ERV transmission.
Mechanisms of XRV and ERV transmission. XRVs are transmitted horizontally (red arrows) either in utero or via infected blood, feces, urine, milk, or saliva. After an XRV invades the germ line, ERVs (green arrows) may be amplified by superinfection or retrotransposition in the host germ line. ERVs that remain infectious can potentially infect naive members of the species. (Koala photographs courtesy of Tad Motoyama [Los Angeles Zoo, Los Angeles, CA].)‏
Alex D. Greenwood et al. Microbiol. Mol. Biol. Rev. 2018; doi: /MMBR