The effect of carvacrol on respiratory syncytial virus infection in mice model: caution in the use of herbal medicines

Background and Objectives: Respiratory syncytial virus (RSV) is one of the most common viruses associated with acute lower respiratory tract infections in infants, young children, and the elderly. Due to a lack of effective anti-viral drugs or vaccines, using an immunomodulatory strategy is probably the best option to decrease the burden of RSV disease. Here, we studied carvacrol as a known immunomodulator on RSV infection outcome in a mice model. Materials and Methods: Balb/c mice were infected by intranasal inoculation of RSV-A2, and treatment started daily 24 h after infection. Mice were sacrificed on day five after infection and experimental analyses were performed to study airway immune cell influx, CD4 and CD8 subtypes, cytokine/chemokine secretion, lung histopathology, and viral load. Results: Results showed that using carvacrol enhanced immune cell influx, cytokine/chemokine production, and virus titer, and aggravated lung pathology. Our result showed that carvacrol administration increased viral titer compared to the RSVPBS group. Also, carvacrol significantly induced IFN-γ production and did not induce IL-10 production. Besides, carvacrol non-significantly increased lymphocytes and monocytes count but did not affect the neutrophil count. Conclusion: Carvacrol at the concentration of 80 (mg/kg) did not show immunomodulatory activity to alleviate the RSV infection outcome. Further research is needed to uncover the effects of the carvacrol intervention on virus replication and immune responses following RSV infection. Many herbal remedies in use contain carvacrol. However, the use of herbal remedies to treat viral respiratory infections such as RSV has to be performed with caution.