Honey as an antiviral agent against respiratory syncytial virus

Abstract

Respiratory syncytial virus is the most frequent cause of hospitalization for viral respiratory infections in infants and young children worldwide. It also severely affects immunocompromised adults and the elderly, however, despite decades of efforts, there is no proven effective treatment for RSV infection and attempts at vaccine development have been hampered by several major obstacles. A large amount of research has established the potent antibacterial activity of honey, but its activity against viral species has been the subject of only a small number of studies. These were with viruses which cause localised infections in which honey could be used topically. Recent studies demonstrating the safety of intrapulmonary administration of honey in sheep and humans raised the possibility of using honey to treat respiratory infections. The aim of this study, therefore, was to extend the knowledge obtained from previous studies of honey’s antiviral activity to its action against RSV. A variety of tests using cell culture were developed to evaluate the susceptibility of RSV to honey. Each test monitored and scored the development of morphological changes to the cells caused by RSV infection to determine whether the honey had any inhibitory effect on these changes. These included tests for: inhibition, where honey was used to treat infected cells; protection, in which the cells were treated with honey prior to infection; neutralisation, in which the virus was directly exposed to the honey for a defined period before being used to inoculate the cells. Pre-treatment of the cells had no effect on the consequent development of cytopathic effect, while the inhibition and neutralisation experiments showed a significant inhibitory effect on the progression of infection, suggesting a direct effect on the virus rather than on the cells, however, further studies are required to confirm this. A wide range of honey types were tested for their inhibitory and neutralising capabilities against RSV and the results suggested that the antiviral activity may be characteristic of more than one type of honey. The activity observed did vary, however, with some types of honey causing greater inhibition of RSV than others. Enzyme-linked immunosorbent assays were also used to quantitatively measure the number of viral antigens in honey-treated and untreated cells. The results confirmed that treatment with honey had caused inhibition of viral replication, there being very little virus detected in honey-treated cells compared with untreated cells infected with RSV. Experiments using quantitative PCR also demonstrated the inhibitory effect of honey on RSV at the transcription level, with significant differences in the mRNA copy numbers of two out of the three viral genes examined. Attempts at isolating the antiviral component in honey demonstrated that the sugar was not responsible for the inhibition of RSV, but that methylglyoxal may play a part in the greater potency of Manuka honeys against RSV. It is concluded from the findings in this study that honey may possibly be an effective antiviral treatment for the therapy of respiratory viral infections, and provides justification for future in vitro studies and clinical trials.