Ranavirus Host Immunity and Immune Evasion

Ranaviruses (RV, Iridoviridae) are now known to infect fish, amphibians, and reptiles, raising considerable ecological and commercial concerns due to the escalating infection prevalence and the resulting die-offs of wild and aquacultural species. Notably, ranaviruses exhibit uncanny capacities to cross host species barriers of their poikilothermic hosts, likely owing to their potent immune evasion mechanisms. In turn, the species infected by these pathogens possess immune systems that are less well understood than those of mammals, and are often comprised of unique immune genes or multiple copy orthologs of the single hallmark mammalian immune factors. Thus, garnering greater insight into ranavirus infection strategies is largely contingent on gaining further insights into host immune barriers faced by these emerging infectious agents. Accordingly, here we coalesce the current state of understanding of the distinct facets of lower vertebrate immune responses to ranaviral infections and underline some of the evasion strategies by which these pathogens circumvent these host defenses.