In vitro antiviral activity of Thymbra spicata L. extract on bovine respiratory viruses (BCoV, BPIV-3, BRSV, BVDV and BoHV-1).

AIMS: Viral pathogens are the primary agents in bovine respiratory disease cases, and there is no direct effective antiviral drug application. Thymbra is a genus of oregano commonly found in Turkey. The primary component (34.9%) of the extract obtained from Thymbra spicata L. is the carvacrol which is used in traditional medicine. This study evaluates the potential antiviral activity and inactivation efficiency of T. spicata L. extract against bovine respiratory viruses, including BCoV, BPIV-3, BRSV, BVDV and BoHV-1. METHODS AND RESULTS: To evaluate its effect on viral replication, viral titres were taken from infected cells treated with non-cytotoxic T. spicata L. extract concentrations (0.75% and 1.5%, 1.32 and 2.64 µg/ml of carvacrol as active ingredient, respectively) and compared to non-treated infected cells. The viruses were treated directly with 1.5% T. spicata L. extract, and the viral titres were evaluated at certain time points to determine the efficiency of direct inactivation. The number of infectious virions for BCoV, BPIV-3, BRSV, BVDV and BoHV-1 treated with 1.5% T. spicata L. extract were decreased by 99.44%, 100.0%, 94.38%, 99.97% and 99.87%, respectively.T. spicata L. extract strongly inhibits the replication of mentioned viruses in a dose-dependent manner in vitro. In addition, T. spicata L. extract shared direct inactivation efficiency on the mentioned viruses in a time-dependent manner. CONCLUSION: This study shows the antiviral efficiency of T. spicata L. on BRD-related viral agents for the first time. The oregano species T. spicata and its main component, carvacrol, may have a potential for antiviral activity in the alternative treatment of respiratory viral diseases in cattle. SIGNIFICANCE AND IMPACT OF THE STUDY: Given the similarity of replication strategies, obtained data suggest the possible efficiency of T. spicata L. on human respiratory viruses.

Ivermectin also inhibits the replication of bovine respiratory viruses (BRSV, BPIV-3, BoHV-1, BCoV and BVDV) in vitro.

Bovine respiratory disease (BRD) complex is an important viral infection that causes huge economic losses in cattle herds worldwide. However, there is no directly effective antiviral drug application against respiratory viral pathogens; generally, the metaphylactic antibacterial drug applications are used for BRD. Ivermectin (IVM) is currently used as a broad-spectrum anti-parasitic agent both for veterinary and human medicine on some occasions. Moreover, since it is identified as an inhibitor for importin α/ß-mediated nuclear localization signal (NLS), IVM is also reported to have antiviral potential against several RNA and DNA viruses. Since therapeutic use of IVM in COVID-19 cases has recently been postulated, the potential antiviral activity of IVM against bovine respiratory viruses including BRSV, BPIV-3, BoHV-1, BCoV and BVDV are evaluated in this study. For these purposes, virus titration assay was used to evaluate titers in viral harvest from infected cells treated with non-cytotoxic IVM concentrations (1, 2.5 and 5 µM) and compared to titers from non-treated infected cells. This study indicated that IVM inhibits the replication of BCoV, BVDV, BRSV, BPIV-3 and BoHV-1 in a dose-dependent manner in vitro as well as number of extracellular infectious virions. In addition, it was demonstrated that IVM has no clear effect on the attachment and penetration steps of the replication of the studied viruses. Finally, this study shows for the first time that IVM can inhibit infection of BRD-related viral agents namely BCoV, BPIV-3, BVDV, BRSV and BoHV-1 at the concentrations of 2.5 and 5 µM. Consequently, IVM, which is licensed for antiparasitic indications, also deserves to be evaluated as a broad-spectrum antiviral in BRD cases caused by viral pathogens.