Japanese Encephalitis Vaccines

Extracellular Vesicles in Flaviviridae Pathogenesis: Their Roles in Viral Transmission, Immune Evasion, and Inflammation

The members of the Flaviviridae family are becoming an emerging threat for public health, causing an increasing number of infections each year and requiring effective treatment. The consequences of these infections can be severe and include liver inflammation with subsequent carcinogenesis, endothelial damage with hemorrhage, neuroinflammation, and, in some cases, death. The mechanisms of Flaviviridae pathogenesis are being actively investigated, but there are still many gaps in their understanding. Extracellular vesicles may play important roles in these mechanisms, and, therefore, this topic deserves detailed research. Recent data have revealed the involvement of extracellular vesicles in steps of Flaviviridae pathogenesis such as transmission, immune evasion, and inflammation, which is critical for disease establishment. This review covers recent papers on the roles of extracellular vesicles in the pathogenesis of Flaviviridae and includes examples of clinical applications of the accumulated data.

m6A modification associated with YTHDF1 is involved in Japanese encephalitis virus infection

N6-methyladenosine (m6A), the most common modification in mammalian mRNA and viral RNA, regulates mRNA structure, stability, translation, and nuclear export. The Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus causing severe neurologic disease in humans. To date, the role of m6A modification in JEV infection remains unclear. Herein, we aimed to determine the impact of m6A methylation modification on JEV replication in vitro and in vivo. Our results demonstrated that the overexpression of the m6A reader protein YTHDF1 in vitro significantly inhibits JEV proliferation. Additionally, YTHDF1 negatively regulates JEV proliferation in YTHDF1 knockdown cells and YTHDF1 knockout mice. MeRIP-seq analysis indicated that YTHDF1 interacts with several interferon-stimulated genes (ISGs), especially in IFIT3. Overall, our data showed that YTHDF1 played a vital role in inhibiting JEV replication. These findings bring novel insights into the specific mechanisms involved in the innate immune response to infection with JEV. They can be used in the development of novel therapeutics for controlling JEV infection.

Japanese Encephalitis Vaccine Acceptance and Strategies for Travelers: Insights from a Scoping Review and Practitioners in Endemic Countries

Japanese encephalitis (JE) remains the cause of vaccine-preventable encephalitis in individuals living in endemic areas and international travelers. Although rare, the disease's high fatality rate emphasizes the need for effective immunization. This review aims to provide updated data on the JE burden between 2017 and 2023, vaccine acceptance, and vaccine strategies for travelers. We prospectively identified studies, using MEDLINE and PubMed, published through 2023. JE incidence has decreased in local populations and remains low among travelers from non-endemic countries. The local JE risk cannot be utilized to determine traveler risk. Adult travelers naïve to JEV infection or immunization may be at potentially higher risk. The JE vaccine acceptance rates among international travelers visiting JE endemic areas range from 0.2% to 28.5%. The cost of the vaccine and low risk perception could be barriers to JE vaccination. For travelers, an accelerated two-dose regimen of inactivated Vero cell JE vaccine (JE-VC) or a single dosage of live attenuated JE vaccine (JE-LV) may be an option. In conclusion, the JE burden among residents and travelers is lower, but the risk is not negligible. Practitioners should prioritize sharing knowledge, increasing awareness, and promoting vaccinations and preventive measures to reduce tourists' risk of JE along their journey.

Flaviviruses in AntiTumor Therapy

Oncolytic viruses offer a promising approach to tumor treatment. These viruses not only have a direct lytic effect on tumor cells but can also modify the tumor microenvironment and activate antitumor immunity. Due to their high pathogenicity, flaviviruses have often been overlooked as potential antitumor agents. However, with recent advancements in genetic engineering techniques, an extensive history with vaccine strains, and the development of new attenuated vaccine strains, there has been a renewed interest in the Flavivirus genus. Flaviviruses can be genetically modified to express transgenes at acceptable levels, and the stability of such constructs has been greatly improving over the years. The key advantages of flaviviruses include their reproduction cycle occurring entirely within the cytoplasm (avoiding genome integration) and their ability to cross the blood-brain barrier, facilitating the systemic delivery of oncolytics against brain tumors. So far, the direct lytic effects and immunomodulatory activities of many flaviviruses have been widely studied in experimental animal models across various types of tumors. In this review, we delve into the findings of these studies and contemplate the promising potential of flaviviruses in oncolytic therapies.

Japanese encephalitis virus induces apoptosis by activating the RIG-1 signaling pathway

Japanese encephalitis virus (JEV) infection can cause brain tissue lesions characterized by neuronal death, and apoptosis is involved in JEV-induced neuronopathy. In the present study, mouse microglia were infected with JEV, and pyknosis with dark-staining nuclei of infected cells was detected using Hoechst 33342 staining. TUNEL staining showed that JEV infection promoted the apoptosis of BV2 cells, and the apoptosis rate was significantly increased at 24-60 hours postinfection (hpi) (P < 0.01) and was the highest at 36 h (P < 0.0001). Western blot results showed that the expression of the Bcl-2 protein in JEV-infected cells was downregulated significantly at 60 hpi (P < 0.001), whereas that of the Bax protein was observably upregulated at 60 hpi (P < 0.001). At the same time, the level of cytochrome c (Cyt c) was significantly increased (P < 0.001), and the expression levels of two apoptosis-related proteins, namely, cleaved caspase-3 (P < 0.01) and caspase-9 (P < 0.001), were elevated significantly. Immunofluorescence staining showed that the amount of Cyt c increased with time after infection. After BV2 cells were infected with JEV, the expression of RIG-1 increased significantly from 24 hpi to 60 h (P < 0.001). The expression of MAVS increased significantly at 24 h (P < 0.001) and decreased gradually from 24 h to 60 hpi. The expression of TBK1 and NF-κB (p65) was not significantly changed. The expression of p-TBK1 and p-NF-κB (p-p65) increased significantly within 24 h (P < 0.001) and decreased from 24 to 60 hpi. The expression levels of IRF3 and p-IRF3 peaked at 24 hpi (P < 0.001) and decreased gradually from 24 to 60 hpi. However, the expression levels of JEV proteins showed no significant change at 24 and 36 hpi but were markedly elevated at 48 and 60 hpi. Interference with the expression of the RIG-1 protein in BV2 cells resulted in a dramatic increase in the expression of the anti-apoptotic protein Bcl-2 (P < 0.05), whereas the pro-apoptotic protein Bax, cleaved caspase-9, and especially cleaved caspase-3 were downregulated (P < 0.05), and viral protein expression was notably reduced (P < 0.05). These results indicate that JEV induces apoptosis through mitochondrial-dependent apoptosis pathways, interfering with the expression of RIG-1 in BV2 cells can inhibit viral replication and inhibit apoptosis.

Mosquito Salivary Proteins and Arbovirus Infection: From Viral Enhancers to Potential Targets for Vaccines

Arthropod-borne viruses present important public health challenges worldwide. Viruses such as DENV, ZIKV, and WNV are of current concern due to an increasing incidence and an expanding geographic range, generating explosive outbreaks even in non-endemic areas. The clinical signs associated with infection from these arboviruses are often inapparent, mild, or nonspecific, but occasionally develop into serious complications marked by rapid onset, tremors, paralysis, hemorrhagic fever, neurological alterations, or death. They are predominately transmitted to humans through mosquito bite, during which saliva is inoculated into the skin to facilitate blood feeding. A new approach to prevent arboviral diseases has been proposed by the observation that arthropod saliva facilitates transmission of pathogens. Viruses released within mosquito saliva may more easily initiate host invasion by taking advantage of the host's innate and adaptive immune responses to saliva. This provides a rationale for creating vaccines against mosquito salivary proteins, especially because of the lack of licensed vaccines against most of these viruses. This review aims to provide an overview of the effects on the host immune response by the mosquito salivary proteins and how these phenomena alter the infection outcome for different arboviruses, recent attempts to generate mosquito salivary-based vaccines against flavivirus including DENV, ZIKV, and WNV, and the potential benefits and pitfalls that this strategy involves.

Growth, Pathogenesis, and Serological Characteristics of the Japanese Encephalitis Virus Genotype IV Recent Strain 19CxBa-83-Cv

Genotype IV Japanese encephalitis (JE) virus (GIV JEV) is the least common and most neglected genotype in JEV. We evaluated the growth and pathogenic potential of the GIV strain 19CxBa-83-Cv, which was isolated from a mosquito pool in Bali, Indonesia, in 2019, and serological analyses were also conducted. The growth ability of 19CxBa-83-Cv in Vero cells was intermediate between that of the genotype I (GI) strain Mie/41/2002 and the genotype V (GV) strain Muar, whereas 19CxBa-83-Cv and Mie/41/2002 grew faster than Muar in mouse neuroblastoma cells. The neuroinvasiveness of 19CxBa-83-Cv in mice was higher than that of Mie/41/2002 but lower than that of Muar; however, there were no significant differences in neurovirulence in mice among the three strains. The neutralizing titers of sera from 19CxBa-83-Cv- and Mie/41/2002-inoculated mice against 19CxBa-83-Cv and Mie/41/2002 were similar, whereas the titers against Muar were lower than those of the other two viruses. The neutralizing titers of JE vaccine-inoculated mouse pool serum against 19CxBa-83-Cv and Muar were significantly lower than those against Mie/41/2002. The neutralizing titers against the three viruses were similar in three out of the five serum samples from GI-infected JE patients, although the titers against Mie/41/2002 were higher than those against 19CxBa-83-Cv and Muar in the remaining two sera samples. In summary, we identified the basic characteristics of 19CxBa-83-Cv, but further studies are needed to better understand GIV JEV.

Japanese Encephalitis Vaccine Generates Cross-Reactive Memory T Cell Responses to Zika Virus in Humans

Objective. Zika virus (ZIKV) and Japanese encephalitis virus (JEV) are mosquito-borne flaviviruses with sequence homology. ZIKV circulates in some regions where JEV also circulates, or where JE vaccination is used. Cross-immunity between flaviviruses exists, but the precise mechanisms remain unclear. We previously demonstrated that T cell immunity induced by the live-attenuated Japanese encephalitis (JE) SA14-14-2 vaccine conferred protective immunity against ZIKV infection in mice, which could even bypass antibody-dependent enhancement. However, the role of T cell immune, especially memory T cell subsets, in cross-reactive immune responses between JE vaccine and ZIKV in humans has not been reported. Methods. We examined central and effector memory CD4+ and CD8+ T cell (TCM and TEM) responses (including degranulation, cytokines, and chemokines) in the presence of JEV and ZIKV, respectively, by using qualified peripheral blood mononuclear cell samples from 18 children who had recently received a two-dose course of JE vaccine SA14-14-2 as well as seven children without JE vaccination. Results. Cross-reactive CD8+ TCM in response to ZIKV was characterized by secretion of IFN-γ, whereas CD8+ TEM did not show significant upregulation of functional factors. In the presence of ZIKV, IFN-γ and TNF-α expression was upregulated by CD4+ TEM, and the expression signature of CD4+ TCM is more cytotoxic potential. Conclusions. We profiled the cross-reactive memory T cell responses to ZIKV in JE vaccine recipients. These data will provide evidence for the mechanism of cross-reactive memory T cell immune responses between JEV and ZIKV and a more refined view of bivalent vaccine design strategy.

Immune response to arbovirus infection in obesity

Obesity is a global health problem that affects 650 million people worldwide and leads to diverse changes in host immunity. Individuals with obesity experience an increase in the size and the number of adipocytes, which function as an endocrine organ and release various adipocytokines such as leptin and adiponectin that exert wide ranging effects on other cells. In individuals with obesity, macrophages account for up to 40% of adipose tissue (AT) cells, three times more than in adipose tissue (10%) of healthy weight individuals and secrete several cytokines and chemokines such as interleukin (IL)-1β, chemokine C-C ligand (CCL)-2, IL-6, CCL5, and tumor necrosis factor (TNF)-α, leading to the development of inflammation. Overall, obesity-derived cytokines strongly affect immune responses and make patients with obesity more prone to severe symptoms than patients with a healthy weight. Several epidemiological studies reported a strong association between obesity and severe arthropod-borne virus (arbovirus) infections such as dengue virus (DENV), chikungunya virus (CHIKV), West Nile virus (WNV), and Sindbis virus (SINV). Recently, experimental investigations found that DENV, WNV, CHIKV and Mayaro virus (MAYV) infections cause worsened disease outcomes in infected diet induced obese (DIO) mice groups compared to infected healthy-weight animals. The mechanisms leading to higher susceptibility to severe infections in individuals with obesity remain unknown, though a better understanding of the causes will help scientists and clinicians develop host directed therapies to treat severe disease. In this review article, we summarize the effects of obesity on the host immune response in the context of arboviral infections. We have outlined that obesity makes the host more susceptible to infectious agents, likely by disrupting the functions of innate and adaptive immune cells. We have also discussed the immune response of DIO mouse models against some important arboviruses such as CHIKV, MAYV, DENV, and WNV. We can speculate that obesity-induced disruption of innate and adaptive immune cell function in arboviral infections ultimately affects the course of arboviral disease. Therefore, further studies are needed to explore the cellular and molecular aspects of immunity that are compromised in obesity during arboviral infections or vaccination, which will be helpful in developing specific therapeutic/prophylactic interventions to prevent immunopathology and disease progression in individuals with obesity.

Interventions for the Prevention and Treatment of Japanese Encephalitis

Purpose of Review

Japanese encephalitis (JE), a clinical indication of JE virus–induced brain inflammation, is the most prevalent cause of viral encephalitis in the world. This review gives a comprehensive update on the epidemiology, clinical features, therapeutic trials and approaches for preventing the spread of JE. It also outlines the different JE vaccines used in various countries and recommendations for administration of JE vaccines.

Recent Findings

According to the WHO, annual incidence of JE is estimated to be approximately 68,000 cases worldwide. It is widespread across Asia–Pacific, with a potential for worldwide transmission. In endemic locations, JE is believed to affect children below 6 years of age, but in newly affected areas, both adults and children are at risk due to a lack of protective antibodies. Various vaccines have been developed for the prevention of JE and are being administered in endemic countries.

Summary

JE is a neuroinvasive disease that causes symptoms ranging from simple fever to severe encephalitis and death. Despite a vast number of clinical trials on various drugs, there is still no complete cure available, and it can only be prevented by adequate vaccination. Various nanotechnological approaches for the prevention and treatment of JE are outlined in this review.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11908-022-00786-1.

Molecular pathogenesis of Japanese encephalitis and possible therapeutic strategies

Japanese encephalitis virus (JEV), a single-stranded, enveloped RNA virus, is a health concern across Asian countries, associated with severe neurological disorders, especially in children. Primarily, pigs, bats, and birds are the natural hosts for JEV, but humans are infected incidentally. JEV requires a few host proteins for its entry and replication inside the mammalian host cell. The endoplasmic reticulum (ER) plays a significant role in JEV genome replication and assembly. During this process, the ER undergoes stress due to its remodelling and accumulation of viral particles and unfolded proteins, leading to an unfolded protein response (UPR). Here, we review the overall strategy used by JEV to infect the host cell and various cytopathic effects caused by JEV infection. We also highlight the role of JEV structural proteins (SPs) and non-structural proteins (NSPs) at various stages of the JEV life cycle that are involved in up- and downregulation of different host proteins and are potentially relevant for developing efficient therapeutic drugs.

Japanese Encephalitis DNA Vaccines with Epitope Modification Reduce the Induction of Cross-Reactive Antibodies against Dengue Virus and Antibody-Dependent Enhancement of Dengue Virus Infection

Infection with viruses belonging to the genus Flavivirus, such as Japanese encephalitis virus (JEV) and dengue virus (DENV), is a worldwide health problem. Vaccines against JEV and DENV are currently available. However, the dengue vaccine possibly increases the risk of severe dengue due to antibody-dependent enhancement (ADE). Moreover, the Japanese encephalitis (JE) vaccine reportedly induces cross-reactive ADE-prone antibodies against DENV, potentially leading to symptomatic dengue. Therefore, it is necessary to eliminate the risk of ADE through vaccination. In this study, we attempted to develop a JE vaccine that does not induce ADE of DENV infection using an epitope modification strategy. We found that an ADE-prone monoclonal antibody cross-reactive to DENV and JEV recognizes the 106th amino acid residue of the E protein of JEV (E-106). The JE DNA vaccine with a mutation at E-106 (E-106 vaccine) induced comparable neutralizing antibody titers against JEV to those induced by the wild-type JE DNA vaccine. Meanwhile, the E-106 vaccine induced 64-fold less cross-reactive ADE-prone antibodies against DENV. The mutation did not compromise the protective efficacy of the vaccine in the lethal JEV challenge experiment. Altogether, the modification of a single amino acid residue identified in this study helped in the development of an ADE-free JE vaccine.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

Investigation of immune response induction by Japanese encephalitis live-attenuated and chimeric vaccines in mice

The Japanese encephalitis (JE) live-attenuated vaccine SA14-14-2 and the chimeric vaccine IMOJEV (JE-CV) are two kinds of vaccines available for use worldwide. JE-CV was previously known as ChimeriVax-JE, that consists of yellow fever vaccine 17D (YFV-17D) from which the structural genes (prM/E) have been replaced with those of SA14-14-2. This study aimed to investigate the neutralizing antibody, protection efficacy, and specific T-cell response elicited by both vaccines in mice. The neutralizing antibodies produced by JE-CV were slightly lower than those produced by SA14-14-2, but the protection conferred by JE-CV was considerably lower in the low vaccine dose immunization group. Furthermore, the JE-CV did not induce a specific T-cell response against JEV NS3, while it did induce a potent antigen-specific T-cell response against the viral backbone vaccine YFV. In conclusion, this study is the first detailed investigation of the cellular immune response to the two vaccines. Enzyme-linked immunospot (ELISPOT) and flow staining suggest a more potent specific T-cell response against the JEV antigen was elicited in mice immunized with SA14-14-2 but not JE-CV. Using heterologous flaviviruses as a live-attenuated vaccine backbone may unlikely generate an optimal T-cell response against the vaccine strain virus and might affect the protective efficacy.

Construction of a Recombinant Japanese Encephalitis Virus with a Hemagglutinin-Tagged NS2A: A Model for an Analysis of Biological Characteristics and Functions of NS2A during Viral Infection

Nonstructural protein 2A (NS2A) of the Japanese encephalitis virus (JEV) contributes to viral replication and pathogenesis; however, a lack of NS2A-specific antibodies restricts studies on the underlying mechanisms. In this study, we constructed a recombinant JEV with a hemagglutinin (HA)-tagged NS2A (JEV-HA/NS2A/∆NS1’) to overcome this challenge. An HA-tag was fused to the N-terminus of NS2A (HA-NS2A) at the intergenic junction between NS1 and NS2A. A peptide linker, “FNG”, was added to the N-terminus of HA-tag to ensure correct cleavage between the C-terminus of NS1 and the N-terminus of HA-NS2A. To avoid the side effects of an unwanted NS1’ tagged with HA (HA-NS1’), an alanine-to-proline (A30P) substitution was introduced at residue 30 of NS2A to abolish HA-NS1’ production. The HA-tag insertion and A30P substitution were stably present in JEV-HA/NS2A/∆NS1’ after six passages and did not exhibit any significant effects on viral replication and plaque morphology. Taking advantage of HA-NS2A, we examined the activities of NS2A during JEV infection in vitro using anti-HA antibodies. NS2A was observed to be localized to the endoplasmic reticulum and interact with viral NS2B and NS3 during virus infection. These data suggest that JEV-HA/NS2A/∆NS1’ can serve as a model for the analysis of the biological characteristics and functions of NS2A in vitro during JEV infection.

Immune Escape Mechanism and Vaccine Research Progress of African Swine Fever Virus

African swine fever virus (ASFV) is the causative agent of the epidemic of African swine fever (ASF), with virulent strains having a mortality rate of up to 100% and presenting devastating impacts on animal farming. Since ASF was first reported in China in 2018, ASFV still exists and poses a potential threat to the current pig industry. Low-virulence and genotype I strains of ASFV have been reported in China, and the prevention and control of ASF is more complicated. Insufficient understanding of the interaction of ASFV with the host immune system hinders vaccine development. Physical barriers, nonspecific immune response and acquired immunity are the three barriers of the host against infection. To escape the innate immune response, ASFV invades monocytes/macrophages and dendritic cells, thereby inhibiting IFN expression, regulating cytokine expression and the body’s inflammatory response process. Meanwhile, in order to evade the adaptive immune response, ASFV inhibits antigen presentation, induces the production of non-neutralizing antibodies, and inhibits apoptosis. Recently, significant advances have been achieved in vaccine development around the world. Live attenuated vaccines (LAVs) based on artificially deleting specific virulence genes can achieve 100% homologous protection and partial heterologous protection. The key of subunit vaccines is identifying the combination of antigens that can effectively provide protection and selecting carriers that can effectively deliver the antigens. In this review, we introduce the epidemic trend of ASF and the impact on the pig industry, analyze the interaction mechanism between ASFV and the body’s immune system, and compare the current status of potential vaccines in order to provide a reference for the development of effective ASF vaccines.

Structural Basis of Zika Virus Helicase in RNA Unwinding and ATP Hydrolysis

The flavivirus nonstructural protein 3 helicase (NS3hel) is a multifunctional domain protein that is associated with DNA/RNA helicase, nucleoside triphosphatase (NTPase), and RNA 5'-triphosphatase (RTPase) activities. As an NTPase-dependent superfamily 2 (SF2) member, NS3hel employs an NTP-driven motor force to unwind double-stranded RNA while translocating along single-stranded RNA and is extensively involved in the viral replication process. Although the structures of SF2 helicases are widely investigated as promising drug targets, the mechanism of energy transduction between NTP hydrolysis and the RNA binding sites in ZIKV NS3hel remains elusive. Here, we report the crystal structure of ZIKV NS3hel in complex with its natural substrates ATP-Mn²⁺ and ssRNA. Distinct from other members of the Flavivirus genus, ssRNA binding to ZIKV NS3hel induces relocation of the active water molecules and ATP-associated metal ions in the NTP hydrolysis active site, which promotes the hydrolysis of ATP and the production of AMP. Our findings highlight the importance of the allosteric role of ssRNA on the modulation of ATP hydrolysis and energy utilization.

Immunogenicity and Protective Ability of Genotype I-Based Recombinant Japanese Encephalitis Virus (JEV) with Attenuation Mutations in E Protein against Genotype V JEV

Genotype V (GV) Japanese encephalitis virus (JEV) has emerged in Korea and China since 2009. Recent findings suggest that current Japanese encephalitis (JE) vaccines may reduce the ability to induce neutralizing antibodies against GV JEV compared to other genotypes. This study sought to produce a novel live attenuated JE vaccine with a high efficacy against GV JEV. Genotype I (GI)-GV intertypic recombinant strain rJEV-E^XZ0934-M41 (E^XZ0934), in which the E region of the GI Mie/41/2002 strain was replaced with that of GV strain XZ0934, was introduced with the same 10 attenuation substitutions in the E region found in the live attenuated JE vaccine strain SA 14-14-2 to produce a novel mutant virus rJEV-E^XZ/SA14142m-M41 (E^XZ/SA14142m). In addition, another mutant rJEV-E^M41/SA14142m-M41 (E^M41/SA14142m), which has the same substitutions in the Mie/41/2002, was also produced. The neuroinvasiveness and neurovirulence of the two mutant viruses were significantly reduced in mice. The mutant viruses induced neutralizing antibodies against GV JEV in mice. The growth of E^XZ/SA14142m was lower than that of E^M41/SA14142m. In mouse challenge tests, a single inoculation with a high dose of the mutants blocked lethal GV JEV infections; however, the protective efficacy of E^XZ/SA14142m was weaker than that of E^M41/SA14142m in low-dose inoculations. The lower protection potency of E^XZ/SA14142m may be ascribed to the reduced growth ability caused by the attenuation mutations.

Potential for Protein Kinase Pharmacological Regulation in Flaviviridae Infections

Protein kinases (PKs) are enzymes that catalyze the transfer of the terminal phosphate group from ATP to a protein acceptor, mainly to serine, threonine, and tyrosine residues. PK catalyzed phosphorylation is critical to the regulation of cellular signaling pathways that affect crucial cell processes, such as growth, differentiation, and metabolism. PKs represent attractive targets for drugs against a wide spectrum of diseases, including viral infections. Two different approaches are being applied in the search for antivirals: compounds directed against viral targets (direct-acting antivirals, DAAs), or against cellular components essential for the viral life cycle (host-directed antivirals, HDAs). One of the main drawbacks of DAAs is the rapid emergence of drug-resistant viruses. In contrast, HDAs present a higher barrier to resistance development. This work reviews the use of chemicals that target cellular PKs as HDAs against virus of the Flaviviridae family (Flavivirus and Hepacivirus), thus being potentially valuable therapeutic targets in the control of these pathogens.