Naturally circulating reoviruses exhibit enhanced intestinal persistence and altered enteric protease dependence compared to lab-adapted strains

Mammalian orthoreoviruses (reoviruses) commonly infect many mammals, persist on surfaces and in bodies of water, and represent a safe model to study enteric viruses. Extensive research has been performed on prototype reovirus strains, specifically T1L and T3D, in murine L929 fibroblasts. However, T1L/T3D were found to have greater sensitivity to endosomal cathepsin L/B than sewage-derived isolates that rely on intestinal trypsin/chymotrypsin to process virions extracellularly prior to infection. To further understand how cultural adaptation affects reovirus characteristics in L929 cells and intestines, replicative capabilities of lab- and sewage-derived reoviruses were measured in L929 cells following exposure of virions to intestinal luminal factors and in the intestinal tract following oral inoculation of mice. In vitro biochemical analysis of post-entry replication steps and in vivo results of early innate and adaptive immune profiles did not distinguish viruses based on source. In contrast, sewage-derived reoviruses were found at higher titers than lab strains in ileal and colonic tissues, luminal content, and fecal shedding. Increased persistence in vivo was associated with greater resistance to proteolysis and infectious stability in the presence of intestinal lumen factors, particularly from the colon. Furthermore, reovirus uncoating in vivo depended not only on intestinal trypsin/chymotrypsin, as previously described, but also on EDTA-sensitive metalloproteases that differentially process lab- and sewage-derived reoviruses. Altogether, these findings demonstrate that environmental reoviruses are optimized for fecal-oral transmission by enhanced extracellular stability and resistance to intestinal proteases, whereas lab strains adapted to infect well in vitro at the cost of reduced robustness in the gut environment.