The mechanism of HEV infection remains largely unknown. This is mainly due to the lack of effective cell culture systems with which to study its biology.
For my doctoral thesis, I studied cutthroat trout virus (CTV), a non-pathogenic fish hepevirus, as a potential substitute or model for HEV. Unlike HEV, CTV replicates efficiently in cell culture, reaching titres of up to 5×10⁷ genomic equivalents per μL within 4–5 days under interferon inhibition.
My study of CTV was divided into two parts: basic research to improve our understanding of the replication cycle of the virus; and applied research involving clearing the model virus using methods such as cold ethanol fractionation, filtration and pasteurisation, which have also been tested on HEV.
Although CTV is a non-enveloped virus, I showed by transmission electron microscopy that intracellular virions are associated with lipids. This suggests that, as is the case for HEV, the envelope is acquired from intracellular membranes.
Unlike HEV, the supernatant of a CTV cell culture contains both enveloped and non-enveloped versions of the virus. Having shown that the envelope of the CTV was very stable, I demonstrated that the non-enveloped CTV did not originate from the enveloped CTV. This means that there is another egress for this form, most likely bacterial lysis.
To assess viral inactivation, I developed tests based on RT-qPCR, immunofluorescence, and immunocytochemistry. Cold ethanol fractionation resulted in a 3-log reduction and pasteurisation of human albumin inactivated more than 3.7 logs of the virus — a greater reduction than that observed for HEV.
As with HEV, CTV replication was also stimulated by 17β-estradiol, which explains the increased virulence observed in pregnant women.
These results, which show the similarities and differences between CTV and HEV, confirm that CTV can be a beneficial model for the hepavirus family, for both clearance methods and basic research.
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