Background: Duck viral hepatitis (DVH) is a highly contagious viral disease affecting ducks. It can be caused by five\nagents, including duck hepatitis A virus genotypes 1 (DHAV-1), 2 (DHAV-2), and 3 (DHAV-3), as well as duck hepatitis\nvirus 2 and duck hepatitis virus 3. Since 2007, DHAV-3 has been known to be the most prevalent in East and South\nAsia. So far, the information regarding the propagation of DHAV-3 in cultured cells is limited. In this study, we\ndescribe the comparative studies on the growth properties of DHAV-3 in primary duck embryo fibroblast (DEF) cells\nusing two different strains: a virulent strain C-GY and an attenuated strain YDF120. The effect of fetal calf serum\n(FCS) and chick serum (CS) on DHAV-3 replication and the mechanism of the inhibitory effect conferred by FCS\nwere also investigated.\nResults: Following serial passages, both C-GY and YDF120 failed to produce cytopathic effect and plaques. The\ncombined quantitative real-time PCR and indirect immunofluorescence staining methods showed that the two\nviruses could be propagated productively in DEF cells. Investigation of the viral growth kinetics revealed that the\ntwo viruses replicated in DEF cells with similar efficiencies, while the viral load of the virulent C-GY strain peaked\nmore rapidly when compared with the attenuated YDF120 strain. Neutralization assay and time-of-drug-addition\nstudy indicated that FCS displayed inhibitory effect on DHAV-3 replication. Analysis on the mechanism of action of\nFCS against DHAV-3 demonstrated that the inhibitory effect was reflected at three steps of the DHAV-3 life cycle\nincluding adsorption, replication, and release.\nConclusions: Both virulent and attenuated DAHV-3 strains can establish noncytocidal, productive infections in DEF\ncells. The virulent strain replicates more rapidly than the attenuated strain in early infection period. FCS has an\ninhibitory effect on DHAV-3 replication, which may be attributed to action of a non-specific inhibitory factor present\nin FCS directly on the virus. These findings may provide new insights into the development of potential antiviral\nagents.
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