In vitro antiviral activity of chestnut and quebracho woods extracts against avian reovirus and metapneumovirus

Field evidences have suggested that a natural extract, containing tannins, could be effective against poultry enteric viral infections. Moreover previous studies have shown that vegetable tannins can have antiviral activity against human viruses. Based on this knowledge three different Chestnut (Castanea spp.) wood extracts and one Quebracho (Schinopsis spp.) wood extract, all containing tannins and currently used in the animal feed industry, were tested for in vitro antiviral activity against avian reovirus (ARV) and avian metapneumovirus (AMPV). The MTT assay was used to evaluate the 50% cytotoxic compounds concentration (CC50) on Vero cells. The antiviral properties were tested before and after the adsorption of the viruses to Vero cells. Antiviral activities were expressed as IC50 (concentration required to inhibit 50% of viral cytopathic effect). CC50s of tested compounds were >200 μg/ml. All compounds had an extracellular antiviral effect against both ARV and AMPV with IC50 values ranging from 25 to 66 μg/ml. Quebracho extract had also evident intracellular anti-ARV activity (IC50 24 μg/ml). These preliminary results suggest that the examined vegetable extracts might be good candidates in the control of some avian virus infections. Nevertheless further in vivo experiments are required to confirm these findings.