Antiviral activity of <i>Eucalyptus globulus</i> and <i>Eucalyptus citriodora</i> essential oils against H5N1 avian influenza virus and infectious bronchitis virus

Purpose: To explore the antiviral potential of Eucalyptus citriodora and Eucalyptus globulus essential oils against zoonotic highly pathogenic avian influenza (HPAI) H5N1 and infectious bronchitis virus. Methods: The extraction process of eucalyptus leaves was carried out using the steam distillation method. The physicochemical properties of both essential oils were determined by gas chromatography (GC) injection. The essential oils were then tested for toxicity and antiviral activity by liquid phase and vapour phase methods in ovo. In addition to specific pathogen-free (SPF)-egg testing, the infectivity of HPAI H5N1 and effectivity of the essential oils in the vapour phase in inhibiting the growth of H5N1 were also tested using MTT assays. Results: The result showed 100 % inhibition by both essential oils against 103 EID50 of H5N1 AI and IBV for all concentrations that were administered through direct contact. In the vapor phase, complete inhibition of 10² EID50 of HPAI H5N1 and IBV viruses was observed at 8 % concentration for both essential oils, as confirmed by the absence of lesions on the embryos and negative HA test result. Conclusion: Eucalyptus essential oils from E. citriodora and E. globulus may serve as potential alternative natural products for combating zoonotic HPAI H5N1 and infectious bronchitis virus (IBV). Further studies are needed to characterize their phytopharmaceutical activity and pathways as novel antiviral agents against these viruses.