Cutthroat trout virus as a surrogate in vitro infection model for testing inhibitors of hepatitis E virus replication

Abstract

Hepatitis E virus (HEV) is one of the most important causes of acute hepatitis worldwide. Although most infections are self-limiting, mortality is particularly high in pregnant women. Chronic infections can occur in transplant and other immune-compromised patients. Successful treatment of chronic hepatitis E has been reported with ribavirin and pegylated interferon-alpha, however severe side effects were observed. We employed the cutthroat trout virus (CTV), a non-pathogenic fish virus with remarkable similarities to HEV, as a potential surrogate for HEV and established an antiviral assay against this virus using the Chinook salmon embryo (CHSE-214) cell line. Ribavirin and the respective trout interferon were found to efficiently inhibit CTV replication. Other known broad-spectrum inhibitors of RNA virus replication such as the nucleoside analog 2'-C-methylcytidine resulted only in a moderate antiviral activity. In its natural fish host, CTV levels largely fluctuate during the reproductive cycle with the virus detected mainly during spawning. We wondered whether this aspect of CTV infection may serve as a surrogate model for the peculiar pathogenesis of HEV in pregnant women. To that end the effect of three sex steroids on in vitro CTV replication was evaluated. Whereas progesterone resulted in marked inhibition of virus replication, testosterone and 17β-estradiol stimulated viral growth. Our data thus indicate that CTV may serve as a surrogate model for HEV, both for antiviral experiments and studies on the replication biology of the Hepeviridae.

Cutthroat Trout Virus—Towards a Virus Model to Support Hepatitis E Research

“…Previous cell culture systems of CTV in CHSE-214 cells reported viral titers between 10 7 and 10 8 geq/mL after 20 days in culture [6], which represented a modest improvement over other cell culture systems reported for HEV. We observed similar replication efficiencies of CTV in ZF4 cells, and less satisfactory replication in SOB-15 cells.…”

“…The genome of CTV is therefore similar in size and organization to that of HEV. CTV has been propagated in CHSE-214 cells [1,2,5,6], with viral titers reaching between 10 7 and 10 8 geq/mL after 20 days of infection [6]. Being similar to HEV, non-pathogenic to humans, and able to replicate in cultured cells, CTV has been proposed as a promising model virus for HEV [2,6].…”

Ribavirin Inhibits In Vitro Hepatitis E Virus Replication through Depletion of Cellular GTP Pools and Is Moderately Synergistic with Alpha Interferon

“…Treatment duration is at least 12 weeks for chronic infections (13) and a minimum of 3 weeks for acute infections (14,15,34) (compare with the current standard of care for hepatitis C, i.e., pegylated IFN-␣ plus RBV for up to 48 weeks, combined with a protease inhibitor for genotype 1 infections [35]). The scientific evidence for these hepatitis E treatments is limited to a number of case series and the in vitro activity against CTV, a HEV surrogate (36). None of these interventions or the superiority of one over the other has been validated in controlled trials yet.…”

Antiviral strategies for hepatitis E virus

“…Another possible strategy to identify novel inhibitors of HEV replication is to use a surrogate virus. We recently reported that the cutthroat trout virus (CTV) may serve as such a surrogate (Debing et al, 2013b). CTV was isolated in 1988 from spawning trout in the western USA (Hedrick et al, 1991) and recent studies revealed that the virus belongs to its own genus in the Hepeviridae family (Smith et al, 2013).…”

“…CTV was isolated in 1988 from spawning trout in the western USA (Hedrick et al, 1991) and recent studies revealed that the virus belongs to its own genus in the Hepeviridae family (Smith et al, 2013). It has a remarkable similarity to HEV, especially when considering the helicase and polymerase sequences (Batts et al, 2011;Debing et al, 2013b). CTV replicates readily in cell culture allowing for RT-qPCR-based virus yield assays to be performed (Debing et al, 2013b).…”