Ayurvedic Antiviral Agents: Overview of Medicinal Plants Perspective

In recent years it has been reported that many of the herbal plants contain antiviral agents which combat human disease that are caused by pathogenic viruses. The natural products which are obtained from plants as antiviral agents against viruses have gone through researches to check the efficacy and potentials of the herbal products in prevention of viral disorders. The viral diseases are challenging for the health of people around the world cause significant increase in mortality and enhance crises. There are many synthetic antiviral drugs which have large number of side effects and have narrow therapeutic window range, while in other hand herbal formulations have minimized side effects. The advantages of herbal formulation over synthetic drugs encourage us to divise and expand new herbal moieties against the emerging viral infections. The medicinal plant contains phytochemicals which have antiviral properties. In this paper the activity of antiviral agents from medicinal plants which have importance in Ayurveda are discussed along with their source.

Keywords: Medicinal Plants; Antiviral Agents; Therapeutic Window Range; Viral Infections; Phytochemicals; Ayurveda

Viral diseases are more threatening to public health day by day. Many number of viral diseases have been reported from different regions of the world [1]. The therapeutic potentials of medicinal plants recapped by various research programs [2]. For humans the plants are the crucial source of medicine. Day by day the demand for traditional medicine is increased. To achieve the health goals it is important to use the traditional medicines as per World Health Organisation. There is about at least 35000 species of the plants which are used for the purpose of medicine. About 700 herbal products are described along with their clinical effects and properties.50 categories of the herbs have been described according to their clinical effect as antiinflammatory, antiviral, antiasthmaticantihelminthic, antipyretic, antiemetic, antipruritic, antidiarrhea, sedative, antiepileptic, haemostatic, analgesic, haemopoietic, promoter of strength, semen and sperm, voice, complexion, wound healing etc [3]. For primary health care millions of people depends on medicinal plant but it is not limited to that it is also for improvement of livelihood and generation of income [4]. Herbal formulations are the basic foundation in many traditional medicinal system worldwide [5]. The active natural ingredients of higher plants have been studied for their potency against viruses on the basis of Siddha and Ayurveda traditional system of medicine; these studies revealed the viruses e.g. feline immunodeficiency virus, coxsackie virus, herpes simplex virus, influenza virus, respiratory syncytial virus, parainfluenza virus etc. The medicinal plant contains several of the phytochemicals constituents which are responsible for their property to treat diseases. Among them some of have antiviral properties. Nowadays people demanding an alternative medicines other than conventional medicine shown by recent survey in developing countries.

A virus is infectious agent or parasite of small size that itself reproduces. Viruses are called as a link between living and nonliving. The multiplication of viruses occurs only in living cells such as plant cell, animal cell and bacterial cell [6]. The genetic material of viruses is DNA or RNA. The genome is encompassed within the protein sheath called as capsid.The genetic material may be double or single stranded. Capsids of viruses are regular arrays of one or a few types of protein. Almost every ecosystem has viruses. A nonbacterial pathogen infecting tobacco plants was described by Dmitri Wanovsky 1892 article. Tobacco Mosaic virus was discovered by Martinus Beijerink in 1898 [7].

The public threat of emerging viruses is increasing day by day. The viral diseases are very dangerous hence the scientists are continuously involved in the researches for the discoveries of antivirals for curing the new pandemics. Nowadays coronavirus is spreading increasingly which is of unknown origin.

Newly emerging viruses are given as below:

Coronavirus:Coronavirus is a single stranded RNA virus. The coronavirus is included in corona viridae family. Inhumans, it causes common cold and complications that include pneumonia and SARS can occur [8].

Ebola virus:The Ebola virus’s transferal occurs from the wild animals and in the humans by human to human transmission. It is Ebola hemorrhagic fever which causes fatal illness in humans. Ebola virus is the member of filoviridae family.

West Nile Virus:It is an example of mosquito borne zoonotic virus caused by change in climate and it belongs to the family of flaviviridae and it is transmitted by mosquitoes.

Nipah virus:It was first revealed in April 1999 in Malaysia on the pigfarm. It caused the outbreak of respiratory and neurological diseases. Symptoms of encephalitis in humans and respiratory in pigs was observed the outbreak [7].

Sin Nombre virus:Sin Nombre virus is related to Hantavirus. The symptoms of the Hantavirus pulmonary syndrome (HPS) are fever, cough, headache, pulmonary edema and death at the end. SNV belongs to genus of Hantavirus of family bunyaviridae. The reservoir of SNV infection is rodent carrier (the deer mouse) the inhalation of virus contaminated deer mouse excretion is the mode of transmission of SNV. About 66.7 percent fatality rate of SNV induced HPS reported in United States.

SARS-coronavirus (SARS):It is caused by SARS-CoV. It is viral respiratory disease. In bats high probability of SARS-CoV is originated on the basis of phylogenetic analysis and in humans it spreads directly or indirectly via animals held in Chinese market.8273 cases and 775 deaths reported in china in the middle of November 2002 & July 2003.

MERS-Coronavirus: MERS-CoV is a novel coronavirus. In 2012 in Saudi Arabia it was isolated out of a patient suffered from acute Pneumonia. The fatality rate of MERS - CoV is higher than SARS-CoV upto30%.1084cases and 439 deaths was reported in March 2015.Through dromedary camel MERS-CoV spreads from bats to human.

Here is the list of major zoonotic viruses [7,8] (Table 1):

Natural antiviral agents are obtained from the medicinal plants which are described in Ayurveda for along with their antiviral property. The extraction of the parts of medicinal plants gives the crude antiviral agents later these crude products can be purified by using purification techniques such as chromatography [9]. These are obtained as active phytochemicals; including polyphenols, terpenoids, coumarins, alkaloids, phytosterols, glycosides, flavonoids, saponins, sulphides, lignans, etc [9,10]. Here are some antiviral agents from medicinal plants including their mechanism of action is explained in Table 2 [3,4,6,11].

The natural antiviral agents obtain from plants as phytochemicals [9]. This phytochemicals acts on the virus during the infection of host cell by virus & inhibits the further viral infection.

The infection of host cell by virus involves following steps [3] (Figure 1):

• The first step is adsorption of virus on the surface of host cell. This occurs due to interaction of glycoprotein present on the surface of virus with trans membrane receptor on host cell surface

• After adsorption penetration of virus through cell wall occurs

• Then the uncoating of virus involves deliverance of genetic material.

• This delivered genetic material integrates or it may remain exists in the nucleus with the host’s genetic material and this interfere with replication, transcription and translation processes and protein synthesis occurs

• These proteins assembles and forms virions and release by the process of exocytosis [3].

The natural antiviral drugs can act on different steps as given above and inhibit viral replication in viral synthesis. The adsorption of virus on the surface of host cell in first step. Inhibition of these step occurs by natural agents such as Quercetin, epigallocatechine-3- gallate, Ajoene, allicin tannin such as prodelphinidin B-2,3,3’-di-O-gallate etc [6,12]. The penetration through cell wall is inhibited by apigenin, ursolicacid, lectins, lignin-carbohydrate complex etc [4]. After uncoating the early enzymes and gene products are formed for control of nucleic acid synthesis. This step is inhibited by antiviral agents such as calanolide A, inophyllum, etc [4,13] which inhibit the reverse transcriptase enzyme. The inhibition of transcription, translation, DNA replication process can be done by Triterpenesaponin, glycyrrhizic acid, meliacarpin, vasicine, scopadulcic acid, acid polysaccharides, quercetin and its derivatives, meliacarpin, scopadulcic acid B etc [10,12]. The viral neuraminase responsible for release of virus from host cell, this neuraminase is inhibited by withaferin A. One more recognized mechanism of action of opposing viruses carrying DNA as genome is the demolition of coating of virus facilitated by natural antivirus such as anthraquinones like aloe emodin [14-19].

Keeping in view it has been concluded that in Ayurveda many of the medicinal plants contain similar phytochemicals that are responsible for their antiviral property. The enzymes which are essential for viral replication are targeted by phytochemicals procured from plants and acts on different stages of viral replication. The mechanism to target virus of many phyto constituents have not been discovered yet. The discoveries & researches on these phytochemicals for their mechanisms to target the viruses are in the progress throughout the globe. In this era of emerging viral infections new bio active moieties should be discovered. The medicinal plants are taken as source for finding of new antiviral agents with potent antiviral activity then conventional antiviral compounds.