Nutraceuticals are naturally occurring compounds in food with health or medicinal value [76]. In an insilico analysis, around 2263 plant-derived compounds were screened and 43 of those compounds had anti-viral potential against ZIKV. Some of the well-known plant-derived compounds which could bind to ZIKV proteins are kanzonol V from licorice root (Glycyrrhiza glabra), cinnamoylechinaxanthol from Echinacea root; cimiphenol from black cohosh (Cimicifuga racemosa), rosemarinic acid from rosemary (Rosmarinus officinalis), lemon balm (Melissa officinalis) and common sage (Salvia officinalis) [77]. Isoquercitrin, which is a flavonoid compound, has been found to interfere with the entry of the virion into the target cells [78]. Curcumin, a bioactive compound in turmeric also prevents ZIKV attachment to cells [79]. Gossypol, a phenolic compound seen in cotton seeds, has anti-ZIKV activity by interacting with the envelope protein domain III of the virus [80]. F-6 and FAc-2 fractions abundant in cyclic diterpenes with aldehyde groups from Dictyota menstrualis, a brown seaweed in Brazil, have potent anti-viral activity against ZIKV [81]. Polyphenols such as delphinidin and epigallocatechin gallate, which are available in natural products such as wine and tea, exhibited antiviral activity against ZIKV in an in vitro model [82,83]. Berberine, an isoquinoline alkaloid seen in Berberis vulgaris, as well as Emodin, an anthraquinone derivative available in Rheum palmatum, Polygonum multiflorum, Aloe vera, and Cassia obtusifolia were found to have anti-viral activity against ZIKV [84]. A flavonoid compound called naringenin seen in citrus plants exhibits anti-ZIKV activity by binding to the protease domain of the NS2B-NS3 protein [85]. Further, anti-ZIKV activity of flavonoids has also been extensively reviewed elsewhere [86]. For example, 6-deoxyglucose-diphyllin, seen in Justicia gendarussa could prevent the facilitation of an acidic environment within the lysosome or endosome that allows the virus to fuse. Further, 6-deoxyglucose-diphyllin was protective against ZIKV infection both in cell culture as well as in an immunocompromised mice model [87]. Hippeastrine hydrobromide seen in Lycoris radiate was found to be protective against the neuronal damage caused by ZIKV along with having other anti-viral activity [88]. Doratoxylon apetalum plant extract, which is already known to have a protective role against oxidative stress in cells, also had anti-viral activity by preventing ZIKV entry into the cells [89]. 25-hydroxy cholesterol seen naturally in the hosts was found to have anti-viral activity and was able to prevent ZIKV associated clinical signs in both mice and macaque models. Similarly, 25-hydroxy cholesterol also inhibited ZIKV infection in human corticoid organs and microcephaly in newborn mice pups [90]. An omega-3 polyunsaturated fatty acid, docosahexaenoic acid (DHA) was found to have a protective effect against ZIKV-induced neuronal damage in a cell culture model [91]. Nutraceuticals investigated for anti-ZIKV activity are listed in Table 2. 3.1. Other Nutraceuticals against ZIKV InfectionHarringtonine is a natural alkaloid from plant genus, Cephalotaxus and has been shown to show antiviral activities against ZIKV [92]. Harringtonine was shown to inhibit early and late-stage infection and inhibits ZIKV binding, entry and replication of virus. Molecular analysis of harringtonine shows that it can interact with ZIKV envelope proteins and blocks viral binding and entry into the host cells [92]. In addition, palmatine, a plant protoberberine alkaloid was shown to inhibit ZIKV infection by blocking viral binding, entry and stability of ZIKV in vero cells [93]. Cinnamic acid, an organic acid isolated from cinnamon twigs was also shown to inhibit ZIKV replication in vero cells, hepatocytes (Huh7), A549 cells, in vitro and in mouse model of interferon receptor-deficient mice (Infagr-/-) [94]. Cinnamic acid greatly improved the survival of ZIKV infected mice. [94]. Indole alkaloids from the seeds of T. Cymosa was also shown to possess anti-ZIKV activity and are not cytotoxic to Vero cells and A549 cells [95]. Further studies are required to elucidate the detailed mechanisms of anti-ZIKV activity of alkaloids in humans. The role of nutraceuticals in blocking ZIKV replication are represented in Figure 1.

Table 2. List of novel nutrient molecules and mechanism of protection against ZIKV infection.

Table 2. List of novel nutrient molecules and mechanism of protection against ZIKV infection.

Nutrient MoleculeZIKV StrainCellsResultMechanism of ProtectionRef.No.Schinus terebinthifolia, Ethanolic fruits’peel extract (STPE) and whole fruits extract (STWFE)MR766 (African Strain) or PE243 (EH) ZIKV strains with 1 MOIHTR-8/SVneo cellsPotential early antiviral effect, inhibited ZIKV entry Resveratrol (present in STWFE and STPE) prevents ZIKV replication and exhibit virucidal activity [96,97]IsoquercitrinPF-25013-18 (2 MOI for A549), and ZIKV MR766MC, viral clone derived African strain MR766-NIID (1 MOI for A549, Huh-7 and 10 MOI for SHSY5Y)A549,
Huh-7,
SH-SY5YPotential inhibitor of ZIKV infection in different human cells testedPlays an anti-ZIKV activity and glycosylated moiety present in Isoquercitrin plays a vital role. Prevents the ZIKV internalization into the host cell (prevents viral entry)[78]Curcumin
(Pretreatment)HD78788 with 0.1, 1, and 1 MOIHeLa, BHK-21, and Vero-EDecreased ZIKV infection in a time and dose dependent mannerInterferes with the ZIKV envelope binding to the cell though viral RNA integrity was maintained[79]Gossypol,
digitonin, and conessinePAN2016, R116265, PAN2015,
FLR, R103451, PRVABC59, PLCal_ZV, IbH 30656, mosquito strain MEX 2–81, and African strain (MR 766) Vero E6 cellsCompared to conessine and digitonin, gossypol exhibited the strong inhibitory activity against 10 different ZIKV strainsGossypol target EDIII of ZIKV and neutralize the infectionConessine and digitonin targets the host cell entry and ZIKV replication stages[80]Dictyota menstrualis (F-6 and FAc-2 fractions)MR 766 with 0.01–1 MOIVero cellsDose-dependent inhibition of ZIKV replication (>74%)F-6 inhibits viral adsorptionFAc-2-strong virucidal potential[81]Polyphenols—Delphinidin (D) and Epigallocate-chin gallate (EGCG)African MR766 and the American PA259459 with ~106 PFUVero cellsD and EGCG shows virucidal effect which decreases the ZIKV infection
The virucidal of D and EGCG was higher in MR766 compared to PA259459 strainInhibition of two different ZIKV strains (MR766 and PA259459) by D and EGCG was different, mainly by EGCG.This may be due to E protein which has different amino acid composition. MR766 lacks glycosylation motif at position 154 and 4 amino acid deletion, which are found in Asian strains of ZIKV [82,83]Berberine and emodinBrazilian Zika virus strain isolated from a febrile patient in northeast Brazil with 106 PFU/mLVero E6 cellsInduces virucidal effect and decreases the ZIKV infection: 160 µM of berberine decreases infectivity by 77.6%, whereas 40 µM of emodin decreases by 83.3%.The compounds act on the ZIKV structure. Hydrodynamic radius of the ZIKV was reduced with the treatment of Berberine and emodin[84]HarringtoninePRVABC59African Green Monkey Kidney cellsInhibits ZIKV entry, replication and virion releaseVirucidal effects, prophylaxis activity[92]PalmatineATCC VR-1843Vero cellsPrevents ZIKV binding and entryVirucidal effects[93]Cinnamic acidAsian ZIKVVero cells, Huh7, A549Prevent ZIKV replicationInihibit RdRp activity[94]Naringenin (NAR)
Treatment after infection Viruses isolated from serum of infected patients in South Brazil (2016) and Northeast (2015).
Human A549 lung epithelial cells: ZIKV (ZV BR 2015/15261, ZV BR 2016/16288, ZV BR 2015/15098, ZIKV PE243, ZIKV MR766) with 0.1 MOI
Human monocyte-derived dendritic cells: ZIKV (ZV BR 2015/15261) with 10 MOIIn vitro NAR was effective against distinct ZIKV lineages (Asian and African) and seems to act during the late phase of the viral life cycleActs on the ZIKV replication or viral assembly on the host cell. Computation analysis, predicts that interaction between NS2B-NS3 protein in ZIKV and naringenin plays a vital role for the anti-ZIKA activity[85]6-deoxyglucose-diphyllin (DGP)HT1080, VERO, and CHME3 cells with ZIKV-MR766 and ZIKV-RVPs at ~1 MOI.
CHME3 cells with PRVABC59, BeH819015, IBH30656, and DAK-ArD-41524 with 1, 0.2, 0.2 and 0.5 MOI, respectivelyInhibits both in vitro and in vivo ZIKV infectionBased on virological and cellular experiments:
Prevents at binding stage of ZIKV to the host cell (fusion) thus preventing the viral contents entry to the cytosol.
Mechanistic studies: Block the acidification in the host cell at the endosomal/lysosomal compartments which prevents ZIKV fusion with the cell membrane[87]Doratoxylum apetalumA549, clinical isolate PF-25013-18 of ZIKV (ZIKV- PF13) with 2 MOI
Huh7.5 cells, Brazilian strain (ZIKV-BR) with 2 MOI
Recombinant Zika virus expressing the GFP reporter gene (ZIKVGFP)Anti-ZIKV activity with non-cytotoxic concentration in human cell linesPrevents internalization of ZIKV particles into the host cell, thus preventing the ZIKV entry into the cell and viral particle inactivation.[89]Docosahexaenoic acid (DHA)SH-SY5Y, ZIKVPE243 with 10 MOIDHA shows neuroprotective and anti-inflammatory potential DHA restores the mitochondrial function and inhibits reactive species production with ZIKV infection[91]Polydatin (natural precursor of resveratrol and commonly found in grape, peanut etc.)Computational based approach: Molecular docking of phytochemical compounds against NS5 or RdRp, RNA dependent RNA polymeraseOut of 5000 phytochemicals screened, Polydatin shows the best binding interaction with NS5 RNA dependent RNA polymerase active site with docking score −18.71 kcal/mol.
Compared to sofosbuvir, Polydatin has more capacity for the receptor binding [75] 3.2. Nutrition and ZIKVThe nutritional status of the host can contribute to the evolution of the viral disease by mutations contributing to virulence [98]. Likewise, the nutritional status of the host can also play a role in the vector-borne disease evolution [99]. Evidence of supportive nutritional therapy has been important in arboviral infections such as dengue, but there are very limited reports surrounding the topic of nutritional parameters in the context of ZIKV infection [100]. There is an interesting hypothesis which states that the neuronal damage associated with ZIKV could result from the retinoid compounds that have leaked from the liver tissue during ZIKV infection [101]. A study found an association between nutrition and motor function in children with palsy; this could also possibly affect the outcomes in infants affected with ZIKV infection [102]. A correlation between ZIKV infection and anemia has been seen in several cases, and in contrast, other reports show no evidence of anemia with ZIKV infection [103,104]. A study using a mice model revealed that protein malnutrition could be a risk factor in developing congenital Zika syndrome. The results of this study are possibly correlated to the fact that undernutrition is commonly seen in regions with major Zika outbreaks such as Brazil [105]. Another interesting entomology study found that blood meal containing ZIKV showed prominent infection in mosquitoes when compared to protein meal containing ZIKV fed mosquitoes [106]. A study showed that folic acid supplementation reduced ZIKV infection in a cell culture model associated with placental barrier and showed improved postnatal outcomes in fetuses from ZIKV infected pregnant mice [107]. Therefore, monitoring folic acid nutrient status in ZIKV prone endemic areas and enabling its supplementation could help to ameliorate the adverse effect on the fetus observed during ZIKV infection [107]. 3.3. Immunological Response to ZIKV InfectionZIKV can evade the innate immune responses generated by the host via suppression of type I interferon and the subsequent activation of interferon-stimulated genes via non-structural viral proteins such as NS5 and NS4A [44,108]. Interferon λ is known to protect against ZIKV infection in female mice in cases of sexual route of transmission [109]. A recent study shows that at least a 12-month interval between an initial Dengue virus infection confers an effective cellular immune response against a subsequent ZIKV infection [110]. There are also contrasting studies that report pre-existing antibodies against the Dengue virus aggravating ZIKV infection in human explant and mouse models [111,112]. However, there is so far no clinical evidence of enhancement of ZIKV in dengue sero-positive patients. Production of IgM, which is the first antibody to appear against the first encounter with a pathogen, is found to be affected in populations with pre-existing antibodies against flavivirus [113]. Pre-existing antibodies against ZIKV can also cause severe outcomes after subsequent dengue infection due to antibody-dependent enhancement (ADE) in humans [114,115]. In vivo and in vitro, Studies have shown that interferon λ could be protective against ZIKV infection in the placenta [116,117,118]. On the other end, a recent study has shown that placental alkaline phosphatase stabilized by binding immunoglobulin protein (Bip) aids ZIKV infection in placental cells [119]. ZIKV activates an inflammatory response following infection by inflammasome complex formation resulting in IL-1β release [120,121,122]. The placenta undergoes extensive inflammatory changes following ZIKV infection with upregulation of cytokines such as IFN-γ and TNF-α and chemokines such as RANTES (regulated on activation, normal T cell expressed and secreted) and VEGFR-2 (vascular endothelial growth factor receptor-2) [123,124]. Toll-like receptor-3 (TLR-3), which a pattern recognition receptor of the innate immune system that senses double-stranded RNA seen during ZIKV replication, is involved in activation of the inflammatory response particularly in astrocytes [125]. Similarly, babies with congenital Zika syndrome were found to be highly associated with single nuclear polymorphisms in TLR-3 or TNF-α (tumor necrosis factor-alpha) alleles [126]. These studies allude to the importance of the inflammatory response in the ZIKV-induced pathological manifestations in the host. Another important component that protects against ZIKV infection is a cell-mediated immune response and its associated neutralizing antibody generation which is crucial for immunity. Meanwhile, immunologically privileged parts of the body such as the gravid uterus might be vulnerable to ZIKV infection [127]. A sero-surveillance report in Fiji and French Polynesia that experienced ZIKV outbreaks in 2013–2014 currently displays a pattern wherein the younger population comprising of children still has neutralizing antibodies against ZIKV but the older population comprising of adults showed a decline in the neutralizing antibody titer [128]. 3.4. ZIKV and InflammationZIKV is known to affect various organs in the body from the eyes to the reproductive organs. ZIKV especially strains from the Asian lineage, are known to produce an inflammatory response in the body [129]. A study in chicken embryo livers showed that ZIKV from Asian lineage (isolated from China) elicited a very intense inflammatory response in comparison to dengue virus infection [130]. ZIKV infection in non-pregnant mice caused acute inflammation of the ovaries without any long-term effects on the overall reproducing ability [131]. An immunocompetent C57BL/6J mice model with intravenous challenge study also suggests that ZIKV induces an inflammatory environment in the blood-brain barrier. Additionally, ZIKV elicits a strong inflammatory response in human retinal epithelial cells and chemokine, CXCL10 was highly expressed following infection [132]. There is also evidence of placentitis in pregnant women following ZIKV infection [124,133]. Transcriptome analysis of human umbilical vein endothelial cells (HUVEC) showed upregulation of several cytokines, chemokines and matrix metalloproteinases on ZIKV infection [134]. There are also cases of ZIKV-induced meningitis, encephalitis and myelitis in certain patients [135]. In a recent study, IL-22 was attributed to inflammation of the brain in newborn mice pups infected with ZIKV [136]. Mice models suggest that ZIKV can cause orchitis and epididymitis via pro-inflammatory cytokines and chemokines [137]. A recent study showed that ZIKV induces IL-1β levels and IL-1 receptor antogonist therapy prevents placental inflammation and fetal neuroinflammation [138]. Overall, ZIKV infection elicits inflammatory response in the host with adverse fetal outcome. 3.5. Cell Death in ZIKV InfectionZIKV is known to initiate apoptosis, in which both intrinsic pathways and extrinsic pathways contribute to cell death in the neuronal progenitor cells, leading to microcephaly [139,140]. The extrinsic pathway of apoptosis is activated by cytokines and death ligands such as FasL while the activation of the intrinsic pathway is by cytochrome C released from damaged mitochondria. Both intrinsic and extrinsic pathways merge into a common pathway by activating effector caspases that trigger apoptosis also known as programmed cell death [141]. Also, activation of the necroptotic pathway via RIPK1/RIPK3 (Receptor-interacting serine/threonine-protein kinase 1/3) and Z-DNA-binding protein 1 (ZBP1) favors succinate dehydrogenase formation in neuronal cells which interfere with ZIKV replication [142]. Pyroptosis is also known to be associated with ZIKV infection by its activation of NLRP3 complex formation, which initiates caspase-1 activation [143,144]. A recent study highlights the mechanism of pyroptosis in neuronal progenitor cells following ZIKV infection [145]. ZIKV replicates, forming complexes inside the endoplasmic reticulum, resulting in large vacuoles in the cytoplasmic compartment of the cell and leads to paraptosis in human epithelial cell lines, human primary fibroblasts and astrocytes [146]. Necrotic cell death involves swelling of internal cellular organelles, which eventually rupture and are released outside the cell [147]. Necrotic lesions involving the brain are also observed in animal models including immunocompetent mice and non-human primates [148,149]. Autophagy, once considered as a cell survival pathway by recycling cellular cargoes via lysosomes to build new cellular components, under certain conditions can activate cell death directly or indirectly [150]. ZIKV causes extensive activation of autophagy by downregulating Akt-mTOR (Protein kinase B- Mammalian target of rapamycin) signaling pathways aiding in replication [151]. In contrast, another study showed that activation of the mTOR pathway inhibits autophagy and facilitates ZIKV replication [152]. Together, ZIKV infection induces apoptosis, necrosis, pyroptosis, paraptosis and autophagy dependent cell death pathways. 3.6. ZIKV and PlacentaStructure and function of the placenta: The placenta is a temporary organ that develops between the fetus and the mother and participates in nutrient transport, waste exchange and metabolism [153]. In humans, the fetal part of the placenta is composed of the placental disc, umbilical cord, amnion and chorion, whereas the maternal part from the endometrium of the uterus is the decidua [154]. The major cell type that predominates in the placenta is the trophoblast, which includes syncytiotrophoblasts, villous cytotrophoblasts, and extravillous trophoblasts that are characterized by a highly invasive nature, supported by the maternal decidual cells [155]. The placental functional units are called villi, formed by an outer layer of trophoblasts with a stromal core [156]. The placental villi participate in nutrient absorption for the growing fetus like the intestinal villi that absorb nutrients from digested food in the gastrointestinal tract [157,158]. Cytotrophoblasts are a layer of cells that cover the stromal core located between the basement membrane and syncytiotrophoblasts [159]. Extravillous trophoblasts are cells that migrate from the villi and are involved in uterine remodeling by forming trophoblast cell columns. Syncytiotrophoblasts are multinucleated cells covering the entire placental units, 2–3 cytotrophoblasts fusing to form syncytiotrophoblasts [160]. Both syncytiotrophoblasts and extravillous trophoblasts are differentiated from the cytotrophoblasts [161]. The stromal core of the placenta is richly supplied with blood vessels that originate from the mesenchymal stem cells and Hofbauer cells (placental macrophages) [161]. 3.7. ZIKV Infection in the Placenta and Its ConsequencesZIKV has been demonstrated to replicate in the human placenta, including the Hofbauer cells and trophoblasts [162,163,164,165,166,167]. T cell immunoglobulin and mucin domain 1 (TIM1), Tyro3 and Axl (tyrosine-protein kinase receptors) are considered the cofactors for viral entry into cells. There is a considerable expression of TIM1 in cytotrophoblasts, fibroblasts, umbilical vein endothelial cells, Hofbauer cells and amniochorionic membranes of the placenta, whereas Tyro3 and Axl are variably expressed in these cells [168]. The first trimester of pregnancy was reported to be most susceptible to ZIKV infection [56,133,169,170], while some reports demonstrated that Congenital Zika Syndrome was also observed with ZIKV infection during the second and the third trimesters of pregnancy [171,172,173]. Placental enlargement is an early clinical feature noticed in ZIKV infected pregnancies [174]. Pregnant women who delivered babies with microcephaly typically exhibit clinical signs of ZIKV infection around the start of mid-gestation (8–16 weeks); this is when maternal blood circulation is well established via the placenta [175]. Breaches in the placental barrier could be detected in placental sections from ZIKV infected women [133]. A study using a cell culture model suggests that ZIKV can breach the placental barrier by disruption of tight junctions between the cells of the placenta. Further, ZIKV virions take a transcytosis route to enter the tightly regulated placental barrier and blood-brain barrier [176]. Another study using placenta samples from ZIKV infected women reported that there are ongoing changes in the tight junctions of the syncytiotrophoblasts with decrease in the claudin 4 expression that leads to potential breaches of the placental barrier [177]. ZIKV could also be transferred from the placenta to the fetus utilizing secretory autophagy [178]. ZIKV infection alters the lipid metabolism of placental cells by favoring lipid droplet deposition, which contributes to the ongoing inflammatory process coupled with mitochondrial dysfunction [124]. Another study reported the association of sphingolipids and deposition of ceramides with ZIKV replication particularly in neuronal progenitor cells [179]. A study in ZIKV infected women showed that the placental samples had an inflammatory state even without the actual presence of ZIKV virion and connects this to the involvement of a modulatory role of anti-inflammatory protein annexin 1 (ANXA1) as a result of ZIKV exposure to the placenta [180]. Further, the presence of non-neutralizing flavivirus antibodies was also shown to facilitate or enhance viral infection and spread to syncytiotrophoblasts via neonatal Fc gamma receptor (FcRn) [181]. Recombination-activating gene-1(RAG-1) knockout mice treated with interferon α/β receptor (IFNAR 1) antibody study shows that neutrophils and macrophages of the dam can play an important role in limiting ZIKV spread to the fetus [182]. A recent study in twins found that trophoblasts from a baby without congenital Zika syndrome had a differential activation of genes which contributed to its ability to mount a better immune response against the infection [183]. Expression of Insulin-like growth factor II (IGF2), which is necessary for the proper development of the baby, was found to be inhibited in placental samples from ZIKV infected women [184]. Researchers were even able to rescue ZIKV in vitro from mesenchymal stem cells derived from the placenta of a woman who had cleared the infection and delivered a baby negative for ZIKV infection alluding to ZIKV persistence [185]. In a normal pregnancy, monocytes are polarized to the M2 state to be compatible with the placenta and uterine environment and generate an anti-inflammatory or immunosuppressive state with potential suppression of type I interferon response, but monocytes are predominantly polarized to the M1 pro-inflammatory phenotype, resulting in adverse outcomes of pregnancy due to ZIKV (African strain) infection [186]. The CD14+CD16+ monocytes in the peripheral circulation are also affected by ZIKV infection, producing a 100-fold increase in the expression of CXCL12 and IL-6 in ZIKV infected women [187].