Cyprinid herpesvirus 3 Evolves In Vitro through an Assemblage of Haplotypes that Alternatively Become Dominant or Under-Represented

Abstract

Viruses are able to evolve in vitro by mutations after serial passages in cell cultures, which can lead to either a loss, or an increase, of virulence. Cyprinid herpesvirus 3 (CyHV-3), a 295-kb double-stranded DNA virus, is the etiological agent of the koi herpesvirus disease (KHVD). To assess the influence of serial passages, an isolate of CyHV-3 (KHV-T) was passaged 99 times onto common carp brain (CCB) cells, and virus virulence was evaluated during passages through the experimental infections of common carp. After 78 CCB passages, the isolate was much less virulent than the original form. A comparative genomic analysis of these three forms of KHV-T (P0, P78 and P99) revealed a limited number of variations. The largest one was a deletion of 1363 bp in the predicted ORF150, which was detected in P78, but not in P99. This unexpected finding was confirmed by conventional PCR and digital PCR. The results presented here primarily suggest that, CyHV-3 evolves, at least in vitro, through an assemblage of haplotypes that alternatively become dominant or under-represented.

Koi herpesvirus (KHV) and KHV disease (KHVD) – a recently updated overview

“…temperatures, cells, hosts, very rapidly. On the other hand it reveals that there are always variants of the same virus with smaller or larger inclusions, deletions or substitutions present beside one most virulent variant, which is principally detected (Klafack et al 2017(Klafack et al , 2019. It seems that small genomic changes, which occur frequently, if not always, are normal and are not essential for virus replication and for virulence in C. carpio (common carp, koi and hybrids with them).…”

“…It seems that small genomic changes, which occur frequently, if not always, are normal and are not essential for virus replication and for virulence in C. carpio (common carp, koi and hybrids with them). The ancestor of KHV possibly originates from Asia and all other KHV variants can return to the Asian lineage after passages in vitro and in vivo (Klafack et al 2019). The recently discovered so called intermediate lineages or variants of KHV in Europe (Bigarr e et al 2009) or Asia (Sunarto et al 2011) may result from the changed, deleted or inserted or incomplete replication of KHV due to environmental conditions.…”

“…Several recombinant vaccines, DNA vaccines and deletion mutant vaccines exist in experimental stages (e.g. Rosenkranz et al 2008;Zhou et al, 2014;Boutier et al 2015;Klafack et al 2019;Schr€ oder et al 2019). Alternatively it was shown that application of the exopolysaccharide (EPS) obtained from Arthrospira platensis (Cyanobacteria) in the water or in the food can stop a KHVD outbreak (metaphylaxis) and can also reduce the intensity of KHVD when delivered over four to six weeks (prophylaxis) prior to infection (Reichert et al 2017).…”

“…Only in some cases the similarity of the entire genome deviated by up to 3% from the majority of the published complete genomes, which was designated as KHV-like or atypically reacting KHV (Engelsma et al 2013). Furthermore, a KHV isolate or KHV detected from organ tissues directly is not a unique and single virus but a bulk of diverse viruses including atypically reacting agents (Klafack et al 2017;Klafack et al 2019). KHV disease as well as infection with KHV are notifiable to the OIE and the EU.…”

Coupling cell culture and next-generation sequencing to study aquaculture viral diseases: a review

“…These entities are obligate intracellular parasites, and therefore viral replication in cell cultures is essential for diagnosis, vaccine design, and in vitro characterization of novel viruses. [1][2][3][4][5][6][7] However stable cell lines for the study of aquatic virology remain scarce. 2 In vitro cell culture systems are an exceptionally important tool in aquaculture viral disease research.…”