Nigella sativa (Black Seed) as a Natural Remedy against viruses

The currently available antiviral agents are associated with serious adverse effects, coupled with the increasing rate of viral resistance to the existing antiviral drugs. Hence, the search for alternative natural remedies is gaining momentum across the globe. Nigella sativa Linnen, also called black seed, is a medicinal plant that is gaining worldwide recognition and has been extensively investigated. The present work is aimed to review the existing literature on the antiviral efficacy of Nigella sativa extracts (oil and bioactive compounds). The findings reveal that numerous articles have been published on Nigella sativa and its beneficial effects against different kinds of diseases. However, the antiviral efficacy of Nigella sativa is yet to be given the proper research attention it deserves.

(Dorra, El-Berrawy, Sallam, & Mahmoud, 2019). In term of antiviral activity against influenza virus (H5N1), the study found that Nigella sativa (black seed) has a higher percentage of inhibition value at the maximum non-cytotoxic concentration when compared to Zingiber officcinale (Ginger), meanwhile in term of antioxidant activity all plant extracts exhibited a good antioxidant activity, however Nigella sativa extract exhibited a higher antioxidant activity than Foeniculum vulgare (Fennel). Moreover, crude and diluted extracts of Nigella sativa and Zizyphus spina-christi Mill plant have been compared for their inhibition effect against broad bean mottle virus (BBMV) on Chenopodium amaranticolor as a local lesion host for the virus. Crude extract of Nigella sativa proved to be more effective than the diluted extract in inhibiting the local lesions produced by (BBMV) when compared to the Zizyphus plant extracts (E. F. Mohamed, 2011). Ibrahim et al., 2017 examined water soluble extracts of black cumin (Nigella sativa) along with other natural spices products such as turmeric (Curcuma longa), black pepper (Piper nigrum), cardamom (Elettaria cardamomum) and aniseed (Pimpinella anisum) for their effect on the growth of pathogenic strains such as Aspergillus parasiticus strains and ability to produce aflatoxin contamination. The study found that black cumin has a moderate antifungal activity but it has a high potential to inhibit and control the production of aflatoxin contamination that is considered to be one of the most toxic substances that fungi produce after fungal infection. Sangi et al., 2018 compared the antihyperglycemic effect of some plants including black seed (Nigella sativa), mushroom (Pleurotus ostreatus), and ginger (Zingiber officinale) with metformin. The study has found that Nigella sativa and ginger have an effect in decreasing the serum glucose levels when compared to metformin and have the ability to regenerate pancreatic beta islets of Langerhans in the pancreas, while other plants such as mushroom can decrease the serum glucose levels but it does not have the ability to regenerate pancreatic beta cells.
However, despite the vast number of published articles on Nigella sativa, a review of its antiviral activity has yet to be conducted to date. Therefore, this paper aims to fill this gap by conducting a narrative review of the literature on the antiviral efficacy of the extracts, oil and bioactive compounds of Nigella sativa against viruses. Although Nigella sativa as a natural remedy has been widely used as an alternative method for the treatment against viruses, it is still necessary to evaluate which therapeutic method and/or which compounds of Nigella sativa is effective in the treatment against viruses by reviewing the available literature which will provide data to determine the suitable combinations of therapeutic methods and compounds that might give great promise in finding a suitable remedy against viruses. In this way, the current study contributes to the Nigella sativa literature by identifying the aspects of its efficacy that needs to be experimentally evaluated.

Limitations of Nigella sativa
Despite all the pharmaco-therapeutics effects of Nigella sativa, some limitations of its usage and production raised during the clinical investigations that can limit its usage and clinical development. Some studies reported mild side effects of Nigella sativa when it was given as a treatment for certain diseases. Nausea, bloating, and burning sensation were observed when functional dyspeptic patients have been given 5 mL of Nigella sativa oil mixed with honey orally daily. These results were reported when this study evaluated the efficacy and safety of this mixture to have a gastro-protective and anti H. pylori activity. (Mohtashami et al., 2015). Other studies that examined Nigella sativa seeds on patients suffering from seasonal allergic rhinitis reported that use of Nigella sativa was effective in mild and moderate allergic rhinitis symptoms reduction, however adverse effects such as nasal dryness and diarrhea were observed in some patients, which are consider minor effects when compared with conventional drugs used for allergic rhinitis (Akhtar, 2016; A. Mohamed, Abdul, & Ahmed Alobaidi, 2012). In another study by Dogar et al., (2009) side effects such as pancreatitis, hyperbilirubinemia, diabetes mellitus, diarrhea and hypofibrinogenemia appeared when children with acute lymphoblastic leukemia were treated with L-asparaginase, while none of these serious effects were observed in patients who received conventional treatment with Nigella sativa seeds in a powder form. However, the study concluded that low side effects associated with the consumptions Nigella sativa seeds were significantly less when compared to conventional therapy and the use of L-asparaginase, thus Nigella sativa has high beneficial properties as an anti-cancer agent if given in combination with other cytotoxic drugs. Some studies link these limitations of Nigella sativa and any herbal medicine to the short duration of treatment, loss to follow-up, small sample size and participants' preferences of herb use form On the other hand, Nigella sativa has a number of limitations regarding its productions. TQ has been reported that it has limited bioavailability and exhibits light and heat sensitivity (Goyal et al., 2017). In addition, TQ is considered as a compound that has a rapid distribution and elimination from plasma when given via intravenous administration, while has relatively slower absorption after oral administration using a rabbit as an animal model (Alkharfy, Ahmad, Khan, & Al-Shagha, 2015). Another limitation reported by Mohammed et al., (2018) was poor water solubility. This limitation is closely linked to the different polarity of the oil and water that directly led to poor bioavailability due to decrease in the absorption rate in the gastrointestinal tract.
To prove safe usage and a good production of Nigella sativa, many efforts need to be undertaken to eliminate these limitations. Therefore, further clinical trials, experimental investigations, drug development and animal studies are required to address these limitations and enhance the therapeutics effects of Nigella sativa.

Antiviral Activity of Nigella sativa Nigella sativa against Herpesviruses
The antiviral efficacy of Nigella sativa and TQ against herpesviruses has been well documented. Herpesviridae is a big family of DNA viruses known to cause various diseases in humans and animals; herpesviruses are a common member of this family, with the α-herpesviruses being the most common subfamily. Herpesviruses are classified into herpes simplex viruses 1 and 2 (HSV-1, HSV-2), with HSV-1 being the cause of

Nigella sativa against Hepatitis C virus
As per the WHO, approximately 71 million people were infected by the Hepatitis C virus (HCV) in 2015; hence, Hepatitis C is seen as a global public health issue that is mainly characterized by the high level of liver enzyme expression. These enzymes are the most obvious signs of hepatic injury because their cytoplasmic level normally increases following liver injury (Hajarizadeh, Grebely, & Dore, 2013. Egypt is one of the countries in the world with a high prevalence rate of HCV based on the morbidity and mortality rates; the highest prevalence percentage Although both studies used different extracts, such as seed oil extract and ethanolic extracts of Nigella sativa, they revealed that Nigella sativa is a safe extract that reduced the viral load and improved the clinical condition of the patients.
On the other hand, the outcome of a study (Oyero et al., 2016) showed that Alpha-zam (α-Zam) can be used as a selective inhibitor of HCV replication. α-Zam, as per previous studies, has a combined formula of a herbal remedy containing 60% Nigella sativa and 40% freshly harvested pure honey as the major constituents (

Nigella sativa against Coronaviruses
Coronavirus was first described in 1931 by Dr. Oskar Seifried, a veterinarian, as a serious threat to animal health (Seifried, 1931). However, it was re-identified in the 1960s as a group of viruses that can cause both animal and human infections (Kahn & McIntosh, 2005). Coronavirus is a positive-sense enveloped single-stranded-RNA virus of the Coronaviridae family; it is classified into 4 recognized genera which are alpha, beta, gamma, and delta coronaviruses ( (Fehr et al., 2015). The ongoing COVID-19 is the latest coronavirus-related infection; it has affected more people than SARS or MERS within a shorter period (Marty & Jones, 2020). Nigella sativa is used for the treatment of respiratory diseases like chest congestion, shortness of breath, bronchospasm, and asthma in folk medicine (Goreja, 2003), while its bioactive compounds are used in pharmacological studies as effective ingredients to prepare drugs (Ahmad et al., 2013).
Nigella sativa extract has been evaluated for its efficacy in preventing the replication of coronavirus (CoV) during active coronavirus infection; the extracts successfully reduced the virus loads in the treated cases (Ulasli et al., 2014). Even though previous studies on the antiviral efficacy of Nigella sativa have shown significant results, the effect of the crude ethanol extract of Nigella sativa against the Avian infectious bronchitis virus (IBV) remains unclear. IBV is a gamma coronavirus that causes upper respiratory tract infection in birds, causing the laying of eggs with weakened and deformed shells. (C. Chen et al., 2014) found that Nigella sativa extract had no significant impact on the virus titres as it failed to inhibit IBV replication when compared to the control.

Nigella sativa against Influenza virus
Influenza viruses belong to the Orthomyxoviridae family; this family can be subgrouped into A, B, and C. They are implicated in most cases of respiratory tract infections that manifest in fever, headache, sneezing, muscle pains, sore throat, and joint pains; more severe conditions, such as pneumonia, are also associated with influenza virus infection (Blumel et al., 2009;Eccles, 2005). Influenza virus infection has been considered the most devastating epidemic that caused the highest mortality in humans. In 1918, the influenza A virus pandemic (Spanish flu) caused the death of approximately 40 to 50 million people (Trilla, Trilla, & Daer, 2008 (Sajid Umar et al., 2015) suggested that clinical signs in H9N2 infected birds showed improvement upon dietary supplementation with either Nigella sativa seeds and TQ, or their combination. The study also reported a decline in clinical symptoms upon supplementation with 3% Nigella sativa seed; the antibody titre was also increased against H9N2 AIV, thereby improving immune response and suppressed viral pathogenicity in the treated turkeys when compared to 1% dietary supplementation. Subsequent studies confirmed this dose-dependent effect as a higher antibody titre was observed with 6% Nigella sativa dietary supplementation compared to 1% and 3% dietary supplementation (Sajid Umar, Munir, et al., 2016). These findings suggested that turkeys fed with Nigella sativa exhibited higher levels of cytokine gene expression, leading to increased antiviral behaviour and suppressed pathogenesis of H9N2 viruses. Another study showed that the combination of TQ and other herbs as a single supplement significantly reduced the clinical signs in turkeys fed with this combination; this was attributed to the TQ content of Nigella sativa which improved the immune response and reduced the viral pathogenicity in the treated birds  Taha, 2011). Also, the study reported that TQ, when fed to turkeys infected with H9N2, showed a lower viral load and increased expression of Interferon-gamma (IFNγ) levels. It may suggest that TQ can stimulate and induce proliferation of cytotoxic T-cells to allow increased viral clearance.
Moreover, avian influenza virus subtype H5N1 has previously been reported to be treated with Nigella sativa extract. Ethanol extract of Nigella sativa showed moderate dose-dependent antiviral activity and prevented the replication of H5N1. Experimental works suggested that the inhibition may be mediated by increasing innate immunity (Dorra et al., 2019). However, another study found that Nigella sativa oil, when used as a vaccine adjuvant against H5N1, can exhibit a non-specific immunostimulant effect and induce cellular immune response that restricts the replication of H5N1 (Mady et al., 2013).

Nigella sativa against plant viruses
A few studies have reported the antiviral efficacy of Nigella sativa extracts against plant viral infections; some of the reported studies are as follows:

Nigella sativa against Broad Bean Mosaic virus
Broad bean (Vicia faba L.) is one of the legumes affected by viruses globally (I. E. T. Mohamed &, El Bushra El Sheikh El Nur, 2010). Broad Bean Mosaic Virus (BBMV) is a member of the Bromoviruses and is considered a common virus in fava bean fields. The antiviral activity of Nigella sativa has been tested against BBMV on Chenopodium amaranticolor plant as a local lesion host both in vitro and in vivo (E. F. Mohamed, 2011). The study proved that the extracts reduced the virus-induced local lesions and increased the in vitro inhibition percentages. On the other hand, the in vivo experiments found that pre-inoculation treatment inhibition was more effective in reducing virus pathogenicity compared to post-inoculation treatment. However, the crude extract achieved higher inhibition percentages compared to the dilutions possibly due to its richness in bioactive compounds ( (Desbiez & Lecoq, 1997). The antiviral activity of Nigella sativa decoction and infusion seeds extract has been examined against ZYMV infection in watermelon seedlings. The outcome of the study showed that Nigella sativa inhibited the progression of ZYMV infection both in vitro and in vivo; it did not just inhibit the clinical signs of virus infection but increased the plant growth parameters. The disease severity, percentage of infection, and viral load were correlated with the observed disease symptoms as well (Elbeshehy, 2017). This result agreed with another study by Abdel-Shafi S (2013) who found that the treatment of squash plants with aqueous Nigella sativa extract improved plant recovery from ZYMV infection and improved the plant growth parameters because Nigella sativa extract was able to induce plant resistance against ZYMV infection. Based on these findings, Nigella sativa extracts can be considered safe and recommendable for use as biological control of plant viruses.

CONCluSiON
The use of natural extracts and derivatives in disease prevention and cure has been on the increase globally due to their high tolerance and low side effects. Nigella sativa is a well-known plant used in folk medicine for many decades now; it is considered a "miracle herb" due to its effectiveness in managing several disease conditions. The available scientific data on Nigella sativa has revealed that Nigella sativa oil, extracts, and components, particularly thymoquinone, can serve as natural remedies for many diseases. Moreover, the extracts of Nigella sativa are proven to exhibit different medicinal properties even though their antiviral activity has not been fully exploited. This review focused on reviewing most of the published studies on the antiviral effects of Nigella sativa, especially those that demonstrated the antiviral activity of Nigella sativa and its bioactive compounds against the different plant, animal, and human viruses. Based on the outcome of the review, further studies are recommended for the development of Nigella sativa as a natural antiviral drug against various viruses. It is hoped that this review would be helpful to the interested researchers in the future, and will motivate further experiments (both in vitro, in vivo, and clinical trials) on the antiviral efficacy of Nigella sativa. This review has some limitations. One of them was the difficulty in finding the full texts of some published papers as only the abstract was published. Moreover, only English-language articles and no other language studies were included in this review.