Key words: Avian influenza virus subtype-H5N1, Antiviral activity, Herbal extracts, RT-PCR. Three commercial products of herbal extracts (Amphiflu-Ex®, Fyto-immune Plus® and Viu-Vet®) were tested for antiviral activity against two Egyptian highly pathogenic avian influenza subtype H5N1 isolates (isolated form backyard poultry) and upon sequencing and phylogenetic analysis, they belonged to clade 2.2.1.2., The antiviral assay for the products was done by using chicken embryo fibroblast (CEF)

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... culture through cytopathic effect (CPE) inhibition assay in two different layouts to elucidate post-exposure and pre-exposure antiviral activity of the products. Amphiflu-Ex® at conc. 50 µl/ml showed significant virucidal activity (100% inhibition) in post-exposure assay for both viral isolates which was further confirmed by quantitative real time RT-PCR method that showed 100% reduction in virus titers for both isolates and further investigation was done on conc. 10 and 20 µl/ml, where the virus titers were decreased by 1-1.27 and 2.72-2.8 logs (Log 10 virus titers) respectively. The maximum non-toxic concentration (MNTC) for the three products which estimated by cytotoxicity assay was 50 µl/ml and TCID50 used for both isolates was 106 copy/100 µl.