Viruses are responsible for a variety of human pathogenesis. Owing to the enhancement of the world population, global travel, and rapid urbanization, and infectious outbreaks, a critical threat has been generated to public health, as preventive vaccines and antiviral therapy are not available. Herbal medicines and refined natural products have resources for the development of novel antiviral drugs. These natural agents have shed light on preventive vaccine development and antiviral therapies. This review intends to discuss the antiviral activities of plant extracts and some isolated plant natural products based on mainly preclinical (in vitro and in vivo) studies. Twenty medicinal herbs were selected for the discussion, and those are commonly recognized antiviral medicinal plants in Ayurveda (Zingiber officinale, Caesalpinia bonducella, Allium sativum, Glycyrrhiza glabra, Ferula assafoetida, Gymnema sylvestre, Gossypium herbaceum, Phyllanthus niruri, Trachyspermum ammi, Withania somnifera, Andrographis paniculata, Centella asiatica, Curcuma longa, Woodfordia fruticose, Phyllanthus emblica, Terminalia chebula, Tamarindus indica, Terminalia arjuna, Azadirachta indica, and Ficus religiosa). However, many viruses remain without successful immunization and only a few antiviral drugs have been approved for clinical use. Hence, the development of novel antiviral drugs is much significant and natural products are excellent sources for such drug developments. In this review, we summarize the antiviral actions of selected plant extracts and some isolated natural products of the medicinal herbs.

Nigella sativa has been marked as precious medicinal herb consisting various bioactive compounds including Thymoquinone and very strengthen evidences can be found in literature in this regard. Nigella sativa has popularized as a miracle medicinal herb against pathogenic microorganisms including human infected deleterious viral species such as Human Immunodeficiency Virus (HIV) and Hepatitis C Virus (HCV). Recent animal studies have proved that, Nigella sativa seed extract can apply against virus species including Murine Cytomegalovirus (MCMV), Papaya Ring Spot Virus, Avian influenza (H9N2), Newcastle disease virus (NDV), Peste des Petits Ruminants (PPR) Virus. It is important to focus on Thymoquinone as main bioactive compound of the Nigella sativa. Among them, anti-cancer effect, cardiovascular effects, gastro-protective effect, anti-diabetic activity and free radicle scavenging activities are the most beneficial effects revealed in recent research studies. Hence, more discreet investigations required for the pharmacological actions of bioactive compounds of the Nigella sativa specially for the drug development.

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