Extracts from Valsonectria inflata, a Soil-Derived Fungus, Inhibit Human Coronavirus OC43 Replication

Coronaviruses are responsible for both severe diseases, such as COVID-19, and mild illnesses, such as the common cold. Because coronaviruses are expected to remain continuously prevalent, alternative therapeutic strategies against coronavirus infections should be developed to respond to newly emerging variants. Since many antibiotics, including penicillin, have been isolated from fungi, we screened fungal extracts for antiviral activity against human coronavirus and found that the extract of Valsonectria inflata (VIE) exhibited antiviral effects against human coronavirus. Western blot analysis showed that VIE treatment decreased coronavirus protein expression. Quantitative RT-PCR (qRT-PCR) and plaque formation assays demonstrated that VIE treatment reduced coronavirus production, while scanning electron microscopy (SEM) analysis further confirmed a decrease in the production of infectious viral particles. Finally, VIE treatment ameliorated coronavirus-induced cytotoxicity. We also analyzed the components of VIE, and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) revealed that VIE contains various secondary metabolites, including terpenoids. These results suggest that VIE may serve as a potential antiviral agent against coronavirus infections.