Research progress on viral accommodation 2009 to 2019. (November 2020)

• Record Type: Journal Article
• Authors: Flegel, T.W.
• Is Part Of: Developmental and comparative immunology. Volume 112(2020)
• Publication Date: 2020-11
• Subjects: Heritable adaptive immunity -- Viral accommodation -- Endogenous viral elements -- Insects -- Crustaceans -- Persistent infections; Immunology -- Periodicals; Developmental immunology -- Periodicals; 616.079
• DOI: 10.1016/j.dci.2020.103771
• Languages: English
• ISSNs: 0145-305X

Abstract

Abstract: The viral accommodation hypothesis for crustaceans and insects was first proposed in 1998/2001, stimulated by observations that shrimp and insects or insect cell lines can coexist with both DNA or RNA viruses without showing any signs of disease (i.e., they tolerate, single to multiple, persistent infections, sometimes for a lifetime). A review of tests of the hypothesis up to 2007 was previously published in DCI. This was followed by a major revision in 2009 when the elusive memory element required by the hypothesis was proposed to reside in non-retroviral fragments of extant viruses, now called endogenous viral elements (EVE) that are autonomously inserted into the host genome as cDNA copied from viral mRNA. Here, progress in research on viral accommodation in crustaceans and insects over the decade following 2009 is reviewed. It culminates with a discussion of exiting research results from insects in 2019 that prove the existence of specific, adaptive and heritable immunity, at least in mosquitoes. It remains to be determined whether the same mechanisms also govern EVE acquisition and its protective RNA production in shrimp. The wide-ranging consequences of the revealed mechanisms for viral disease control in economic crustaceans and insects is discussed. Highlights: Insects and crustaceans specifically tolerate one or more viruses without signs of disease. The phenomenon was called viral accommodation in 1998, but the mechanism was unknown. In 2009, it was proposed to involve genomic, endogenous viral elements (EVE) that induce RNAi. If so, protective EVE in germ cell genomes would allow for heritable immunity. Recent research with mosquitoes confirms these proposals.