Rosemary vs RSV

Shin, Choi, Ryu, Lee, Kim, Choi, Chang, Lee, Jang, and Inn (2013) conducted a study testing the effectiveness of carnosic acid in treating human respiratory syncytial virus (hRSV).  At the time of the study, there was no vaccine and no effective study.  They tested three herbs, the other two were not very effective against hRSV so they just used rosemary in this study.  They extracted carnosic acid, rosmarinic acid, and butalinic acid but focused the study on carnosic acid.  They also determined carnosol has no effect on hRSV.  The authors also evaluated cytotoxicity and determined there was minimal cell degradation due to toxicity. 

The results using carnosic acid against hRSV were effective.  After two days at a dose of 20 micrograms per milliliter, the virus had reduced by 26-fold.  At a dose of 50 midcr50 micrograms the number had risen to 1160-fold.  After four days at the 50 dose, there was no virus remaining. It was effective against both a and b type hRSV viruses.  However effective this was against hRSV, they tested it against the flu and had no effect suggesting it has a very specific way of working against some viruses.  Treatment 8 and 12 hours after infection were still effective at 70% and 50%.  

They also tested using pretreatment and the results suggested carnosic acid may inhibit hRSV infection.  While they still do not fully understand how it works, they think because it was ineffective against influenza A, it must attack the virus itself rather than protect the host cells.  For this same reason, they believe it does not attack the RNA of a virus.  The current thinking it is works against proteins which inhibits RNA synthesis.
 
Shin, H., Choi, M. Ryu, B., Lee, N., Kim, H., Choi, H., Chang, J., Lee, K. T., Jang, D. S., and Inn, K. (2013). Antiviral activity of carnosic acid against respiratory syncytial virus.  Virology Journal, 10:303.