VIRAL ACCOMMODATION: A NEW MECHANISM FOR DISEASE CONTROL IN SHRIMP AQUACULTURE

Abstract

Field observations and the results of laboratory experiments prior to 1998 indicate that shrimp are capable of specifc, adaptive responses to viral pathogens that could not be explained by the existing knowledge and understanding of their defence against viruses. Tis was evident from their ability to specifcally tolerate single or multiple viruses in persistent infections, without showing signs of disease. The specifcity of their responses implied that they possessed an unknown type of memory for tolerated viruses, even though shrimp do not produce antibodies. Tolerance is common to crustaceans and insects, and the words “viral accommodation” were chosen to describe it and to encompass the meanings of viral “lodging and support” in a balanced, co-evolutionary interaction. It was proposed that viral accommodation allowed host animals to harbour one or more viruses in persistent infections (sometimes for a lifetime) with minimal negative efects on health. It allowed for positive evolutionary selection of both reduced pathogen virulence and higher host tolerance over time, such that the host and viral pathogen could eventually reach an evolutionary climactic state of innocuous coexistence. In 2009, based on research since 1998, the viral accommodation hypothesis underwent a major revision in which it was proposed that shrimp had the inherent ability to (1) recognize invading viruses, (2) copy pieces of the viral genetic material into DNA fragments, (3) insert these DNA fragments into their own genome as specifc memory elements called endogenous viral elements (EVE) and (4) use EVE for production of anti-viral molecules that could interfere with viral growth and reproduction. The process would specifcally reduce the quantity, but not eliminate the originating virus. From 2009 to 2019, research has proven such a mechanism for viral accommodation occurs in insects and I reviewed this technically in the journal Developmental and Comparative Immunology in 2020. Here, I will give a brief, non-technical review of the history of viral accommodation as background and then focus on potential applications that will be of interest to shrimp culturists should it be confrmed that the mechanisms discovered in insects are paralleled in shrimp.