Ocimum Tenuiflorum L. (Lamiaceae) Syn. O. sanctum L. (Tulsi)

Ocimum sanctum or Tulsi has been used for thousands of years for its diverse therapeutic activities, and is known as the “Queen of herbs” or the legendary “Incomparable one” of India with strong aroma and astringent taste. It is the holiest and most cherished plant for its healing and health-promoting properties and in TM, Tulsi is known as an adaptogen that balances different processes in the body and helps in adapting stress. Ayurveda treats it as a kind of “elixir of life” and is believed to promote longevity and a healthy body. Thus, extracts from Tulsi are used in many Ayurvedic remedies including the common cold, headache, stomach ailments, inflammation and heart disease (74). Several studies with O. sanctum leaf extracts showed therapeutic, prophylactic, and virucidal activities. A study in ovo model indicated its therapeutic activity against H9N2 virus by reducing the infection level (75); while crude extracts or individual compounds isolated from Tulsi have a wide spectrum of antiviral activity against HSV, Adenovirus, Coxsackievirus B1, and Enteroviruses (76). Tulsi is used in diverse formulations including mouthwash, sanitizer and water purifiers (77). The purified components apigenin, linalool, and ursolic acid of O. basilicum showed a broad spectrum of antiviral activities against DNA viruses (HSV, adenoviruses, hepatitis B virus) and RNA viruses (Coxsackievirus B1, Enterovirus 71), among which ursolic acid showed the strongest activity against HSV (40), ADV-8, CVB1, and EV71 (76). Crude, terpenoid, and polyphenol-rich extract of O. sanctum showed significant virucidal activity (p < 0.001–0.01) and was found to decrease the virus genome copy numbers at the lowest dose up to 72 h post-infection (77). Recently, molecular docking studies also suggest that tulsinol A-G and dihydro-dieuginol B as potential inhibitors of SARS Coronavirus Main Protease (Mpro) and Papain-like Protease (PLpro), indicating that O. sanctum can be used as preventive against CoV due to its potential immunomodulatory, ACE2 blocking and viral replication inhibition properties (78).