Infectious bronchitis virus (IBV) is a pathogenic chicken coronavirus, according to Christie Chen of Oxford College of Emory University and co-authors there and The Johns Hopkins University School of Public Health and Amarillo College.

Reporting in BMC Veterinary Research, they explain that currently, vaccination against IBV is only partially protective and that better preventions and treatments are needed.

Plants produce antimicrobial secondary compounds, which may be a source for novel anti-viral drugs. Non-cytotoxic, crude ethanol extracts of Rhodiola rosea (goldenroot) roots, Nigella sativa (black cumin) seeds and Sambucus nigra (common elderberry) fruit were tested for anti-IBV activity, since these safe, widely used plant tissues contain polyphenol derivatives that inhibit other viruses.

Dose–response cytotoxicity curves on Vero cells using trypan blue staining determined the highest non-cytotoxic concentrations of each plant extract.

To screen for IBV inhibition, cells and virus were pre-treated with extracts, followed by infection in the presence of extract. Viral cytopathic effect was assessed visually following an additional 24 hours incubation with extract. Cells and supernatants were harvested separately and virus titres were quantified by plaque assay.

Variations of this screening protocol determined the effects of a number of shortened S. nigra extract treatments. Finally, S. nigra extract-treated virions were visualised by transmission electron microscopy with negative staining.

Virus titre from infected cells treated with R. rosea and N. sativa extracts were not substantially different from infected cells treated with solvent alone.

However, treatment with S. nigra extracts reduced virus titres by four orders of magnitude at a multiplicity of infection (MOI) of 1 in a dose-responsive manner. Infection at a low MOI reduced viral titres by six orders of magnitude and pre-treatment of virus was necessary, but not sufficient, for full virus inhibition.

Electron microscopy of virions treated with S. nigra extract showed compromised envelopes and the presence of membrane vesicles, which suggested a mechanism of action.

These results demonstrate that S. nigra extract can inhibit IBV at an early point in infection, probably by rendering the virus non-infectious, concluded Chen and co-authors. They add that their findings also suggest future studies using S. nigra extract to treat or prevent IBV or other coronaviruses are warranted.

Reference

Chen C., D.M. Zuckerman, S. Brantley, M. Sharpe, K. Childress, E. Hoiczyk and A.R. Pendleton. 2014. Sambucus nigra extracts inhibit infectious bronchitis virus at an early point during replication. BMC Veterinary Research. 10:24. doi:10.1186/1746-6148-10-24

February 2014