Inactivation of Viruses by Charged Cinnamaldehyde Nanoemulsions

Viral pathogens are a considerable public health burden, and so inactivating viruses in the environment is critical. This study compared the antiviral activity of cinnamaldehyde nanoemulsions (CNE) and cinnamaldehyde oil (CNO) on a non-enveloped norovirus surrogate bacteriophage (MS2) and an enveloped human coronavirus 229E (HuCoV-229E). MS2 bacteriophage and HuCoV-229E were treated with different concentrations of CNE or CNO (0.5-3.5%). After treatment for 1 h, the reduction in MS2 numbers was significantly less for the CNE than for the CNO. For instance, the log reductions in MS2 numbers were 4.02 ± 0.10 and 2.78 ± 0.34 PFU/mL after treatment with 3.5% and 0.5% of CNO, whereas they were only 1.54 ± 0.08 and 0 PFU/mL after treatment with the equivalent CNE, respectively. Conversely, a significant reduction in HuCoV-229E was observed for the nanoemulsion-based treatment at high cinnamaldehyde levels. Specifically, when treated with 0.5% cinnamaldehyde, there was a 1.35 ± 0.23 and 3.08 ± 0.17 log PFU/mL reduction for the CNE and CNO treatments, but when treated with 2.5% cinnamaldehyde, there was a 5.98 ± 0.12 and 4.43 ± 0.38 log PFU/mL reduction, respectively. These results suggest that the efficiency of the essential oil as a disinfectant against coronavirus-229E can be increased when it is incorporated in a nanoemulsion at an appropriate concentration. The better efficacy of the nanoemulsion formulations against coronavirus-229E than against MS2 bacteriophage may have been because the cinnamaldehyde oil droplets could penetrate into and deactivate enveloped viruses more effectively than non-enveloped ones.