Neurological manifestations of Flaviviridae, Togaviridae, and Peribunyaviridae as vector-borne viruses.

Vector-borne viruses pose a significant health problem worldwide, as they are transmitted to humans through the bite of infected arthropods such as mosquitoes and ticks. In recent years, emerging and re-emerging vector-borne diseases have gained attention as they can cause a wide spectrum of neurological manifestations. The neurological manifestations of vector-borne viruses encompass a board spectrum of clinical manifestations, ranging from mild and self-limiting symptoms to severe and life-threatening conditions. Common neurological complications include viral encephalitis, acute flaccid paralysis, aseptic meningitis, and various neuromuscular disorders. The specific viruses responsible for these neurological sequelae vary by geographic region and include Orthoflavivirus nilense, Zika virus, dengue virus, chikungunya virus, Japanese encephalitis virus, and tick-borne encephalitis virus. This review focuses on the pathogenesis of these neurologic complications and highlights the mechanisms by which vector-borne viruses invade the central nervous system and trigger neuroinflammatory responses. Diagnostic challenges and strategies for early detection of neurological manifestations are discussed, emphasising the importance of clinical suspicion and advanced laboratory testing.

Orthoflavivirus Lammi in Russia: Possible Transovarial Transmission and Trans-Stadial Survival in Aedes cinereus (Diptera, Culicidae).

In the last few years, there has been a dramatic increase in the number of discovered viruses that are transmitted by arthropods. Some of them are pathogenic for humans and mammals, and the pathogenic potential of others is unknown. The genus Orthoflavivirus belongs to the family Flaviviridae and includes arboviruses that cause severe human diseases with damage to the central nervous system and hemorrhagic fevers, as well as viruses with unknown vectors and viruses specific only to insects. The latter group includes Lammi virus, first isolated from a mosquito pool in Finland. It is known that Lammi virus successfully replicates in mosquito cell lines but not in mammalian cell cultures or mice. Lammi virus reduces the reproduction of West Nile virus during superinfection and thus has the potential to reduce the spread of West Nile virus in areas where Lammi virus is already circulating. In this work, we isolated Lammi virus from a pool of adult Aedes cinereus mosquitoes that hatched from larvae/pupae collected in Saint Petersburg, Russia. This fact may indicate transovarial transmission and trans-stadial survival of the virus.

Tick-virus interactions: Current understanding and future perspectives.

Ticks are the primary vector of arboviruses in temperate climates worldwide. They are both the vector of these pathogens to humans and an integral component of the viral sylvatic cycle. Understanding the tick-pathogen interaction provides information about the natural maintenance of these pathogens and informs the development of countermeasures against human infection. In this review, we discuss currently available information on tick-viral interactions within the broader scope of general tick immunology. While the tick immune response to several pathogens has been studied extensively, minimal work centres on responses to viral infection. This is largely due to the high pathogenicity of tick-borne viruses; this necessitates high-containment laboratories or low-pathogenicity substitute viruses. This has biased most research towards tick-borne flaviviruses. More work is required to fully understand the role of tick-virus interaction in sylvatic cycling and transmission of diverse tick-borne viruses.

Encephalitic Arboviruses of Africa: Emergence, Clinical Presentation and Neuropathogenesis.

Many mosquito-borne viruses (arboviruses) are endemic in Africa, contributing to systemic and neurological infections in various geographical locations on the continent. While most arboviral infections do not lead to neuroinvasive diseases of the central nervous system, neurologic diseases caused by arboviruses include flaccid paralysis, meningitis, encephalitis, myelitis, encephalomyelitis, neuritis, and post-infectious autoimmune or memory disorders. Here we review endemic members of the Flaviviridae and Togaviridae families that cause neurologic infections, their neuropathogenesis and host neuroimmunological responses in Africa. We also discuss the potential for neuroimmune responses to aide in the development of new diagnostics and therapeutics, and current knowledge gaps to be addressed by arbovirus research.

Establishment and characterization of a cell line from Ghanaian Aedes aegypti (Diptera: Culicidae) focusing on Aedes-borne flavivirus susceptibility.

Mosquitoes are generally considered one of the most important vectors of arboviruses, with Aedes aegypti regarded as the most important in transmission of yellow fever and dengue viruses. To investigate why there are differences in the incidence of dengue fever and Zika in different geographical areas and an absence of outbreaks in Ghana in spite of an abundance of A. aegypti mosquitoes, we established a continuous cell line from embryonic cells of A. aegypti collected in Ghana and assessed its susceptibility to dengue, yellow fever, and Zika viruses. The new cell line (designated AeAe-GH98), having an adhesive spindle-shaped web-like morphology, was serially subcultured in both VP-12 and Schneider's medium supplemented with 10% heat-inactivated fetal bovine serum. AeAe-GH98 cells were found to have a population doubling time of 1.3 d during exponential growth. The mosquito colony used to establish the cell line was confirmed to have originated from Africa using microsatellite assay. In terms of susceptibility to Aedes-borne flaviviruses, AeAe-GH98 cells were found to have different degrees of susceptibility to yellow fever, Zika, and dengue virus infection and propagation. While susceptibility of AeAe-GH98 cells to yellow fever and Zika viruses was comparable with that of C6/36 cells, susceptibility to dengue virus was significantly lower. This cell line will serve as a useful tool for determining molecular factors influencing virus-vector susceptibility in vitro.

Evidence that the second human pegivirus (HPgV-2) is primarily a lymphotropic virus and can replicate independent of HCV replication.

The second human pegivirus HPgV-2 is a novel blood-borne virus that is strongly associated with the hepatitis C virus (HCV) infection. However, the molecular evidence for their association as well as the natural history and tissue tropism of HPgV-2 remain to be elucidated. In this longitudinal study, a total of 753 patients including 512 HIV-1 and HCV co-infected patients were enrolled to characterize the natural history of HPgV-2 infection. Peripheral blood mononuclear cells (PBMCs) and liver biopsies were collected to determine the tissue tropism of HPgV-2 using immunohistochemical staining of the HPgV-2 antigen and in situ hybridization of HPgV-2 RNA. We documented both persistent HPgV-2 infection with the presence of HPgV-2 viral RNA and antibodies up to 4.6 years and resolved HPgV-2 infection, accompanied by a simultaneous decline of anti-HPgV-2 antibodies and clearance of HPgV-2 viremia. Furthermore, we observed the clearance of HCV, but not HPgV-2, by treatment with direct-acting antivirals (DAAs). Biochemical tests and pathological analyses did not reveal any indication of hepatic impairment caused by HPgV-2. HPgV-2 RNA and nonstructural antigen were detected in the lymphocytes, but not in the hepatocytes present in the liver biopsy samples. In addition, both positive- and negative-strand HPgV-2 RNAs were detected in PBMCs, especially in B cells. The present study is the first to provide evidence that HPgV-2 is a lymphotropic, but not a hepatotropic virus and that HPgV-2 replication is independent of HCV viremia. These new findings let us gain insights into the evolution and persistent infection of RNA viruses in humans.

Roles of secretory glycoproteins in particle formation of Flaviviridae viruses.

The family Flaviviridae comprises four genera, namely, Flavivirus, Pestivirus, Pegivirus, and Hepacivirus. These viruses have similar genome structures, but the genomes of Pestivirus and Flavivirus encode the secretory glycoproteins Erns and NS1, respectively. Erns plays an important role in virus particle formation and cell entry, whereas NS1 participates in the formation of replication complexes and virus particles. Conversely, apolipoproteins are known to participate in the formation of infectious particles of hepatitis C virus (HCV) and various secretory glycoproteins play a similar role in HCV particles formation, suggesting that there is no strong specificity for the function of secretory glycoproteins in infectious-particle formation. In addition, recent studies have shown that host-derived apolipoproteins and virus-derived Erns and NS1 play comparable roles in infectious-particle formation of both HCV and pestiviruses. In this review, we summarize the roles of secretory glycoproteins in the formation of Flaviviridae virus particles.

Equine Parvovirus-Hepatitis Frequently Detectable in Commercial Equine Serum Pools.

An equine parvovirus-hepatitis (EqPV-H) has been recently identified in association with equine serum hepatitis, also known as Theiler's disease. This disease was first described by Arnold Theiler in 1918 and is often observed after applications with blood products in equines. So far, the virus has only been described in the USA and China. In this study, we evaluated the presence of EqPV-H in several commercial serum samples to assess the potential risk of virus transmission by equine serum-based products for medical and research applications. In 11 out of 18 commercial serum samples, EqPV-H DNA was detectable with a viral load up to 105 copies/mL. The same serum batches as well as three additional samples were also positive for antibodies against the EqPV-H VP1 protein. The countries of origin with detectable viral genomes included the USA, Canada, New Zealand, Italy, and Germany, suggesting a worldwide distribution of EqPV-H. Phylogenetic analysis of the EqPV-H NS1 sequence in commercial serum samples revealed high similarities in viral sequences from different geographical areas. As horse sera are commonly used for the production of anti-sera, which are included in human and veterinary medical products, these results implicate the requirement for diagnostic tests to prevent EqPV-H transmission.

First description of Theiler's disease-associated virus infection and epidemiological investigation of equine pegivirus and equine hepacivirus coinfection in Brazil.

Recent advances in the study of equine pegivirus (EPgV), Theiler's disease-associated virus (TDAV) and equine hepacivirus (EqHV) highlight their importance to veterinary and human health. To gain some insight into virus distribution, possible risk factors, presence of liver damage and genetic variability of these viruses in Brazil, we performed a cross-sectional study of EPgV and TDAV infections using a simultaneous detection assay, and assessed EqHV coinfection in different horse cohorts. Of the 500 serum samples screened, TDAV, EPgV and EPgV-EqHV were present in 1.6%, 14.2% and 18.3%, respectively. EPgV-positive horses were present in four Brazilian states: Espírito Santo, Mato Grosso do Sul, Minas Gerais and Rio de Janeiro. Serum biochemical alterations were present in 40.4% of EPgV-infected horses, two of them presenting current liver injury. Chance of infection was 2.7 times higher in horses ≤5 years old (p = 0.0008) and 4.9 times higher in horses raised under intensive production systems (p = 0.0009). EPgV-EqHV coinfection was 75% less likely in horses older than 5 years comparatively to those with ≤5 years old (p = 0.047). TDAV-positive animals were detected in different horse categories without biochemical alteration. Nucleotide sequences were highly conserved among isolates from this study and previous field and commercial product isolates (≥88% identity). Tree topology revealed the formation of two clades (pp = 1) for both EPgV and TDAV NS3 partial sequences. In conclusion, the widespread presence of EPgV-RNA suggests an enzootic infection with subclinical viremia in Brazil. Horse management can influence virus spread. This first report of TDAV-infected horses outside the USA reveals the existence of subclinical viremic horses in distant geographical regions. EPgV and TDAV have similar circulating isolates worldwide. These findings contribute to global efforts to understand the epidemiology and pathogenesis of these equine viruses.

Regulation of Virus Replication and T Cell Homeostasis by N6-Methyladenosine.

RNA modifications are abundant in eukaryotes, bacteria, and archaea. N6-methyladenosine (m6A), a type of RNA modification mainly found in messenger RNA (mRNA), has significant effects on the metabolism and function of mRNAs. This modification is governed by three types of proteins, namely methyltransferases as "writers", demethylases as "erasers", and specific m6A-binding proteins (YTHDF1-3) as "readers". Further, it is important for the regulation of cell fate and has a critical function in many biological processes including virus replication, stem cell differentiation, and cancer development, and exerts its effect by controlling gene expression. Herein, we summarize recent advances in research on m6A in virus replication and T cell regulation, which is a rapidly emerging field that will facilitate the development of antiviral therapies and the study of innate immunity.

Virus discovery reveals frequent infection by diverse novel members of the Flaviviridae in wild lemurs.

Lemurs are highly endangered mammals inhabiting the forests of Madagascar. In this study, we performed virus discovery on serum samples collected from 84 wild lemurs and identified viral sequence fragments from 4 novel viruses within the family Flaviviridae, including members of the genera Hepacivirus and Pegivirus. The sifaka hepacivirus (SifHV, two genotypes) and pegivirus (SifPgV, two genotypes) were discovered in the diademed sifaka (Propithecus diadema), while other pegiviral fragments were detected in samples from the indri (Indri indri, IndPgV) and the weasel sportive lemur (Lepilemur mustelinus, LepPgV). Although data are preliminary, each viral species appeared host species-specific and frequent infection was detected (18 of 84 individuals were positive for at least one virus). The complete coding sequence and partial 5' and 3' untranslated regions (UTRs) were obtained for SifHV and its genomic organization was consistent with that of other hepaciviruses, with one unique polyprotein and highly structured UTRs. Phylogenetic analyses showed the SifHV belonged to a clade that includes several viral species identified in rodents from Asia and North America, while SifPgV and IndPgV were more closely related to pegiviral species A and C, that include viruses found in humans as well as New- and Old-World monkeys. Our results support the current proposed model of virus-host co-divergence with frequent occurrence of cross-species transmission for these genera and highlight how the discovery of more members of the Flaviviridae can help clarify the ecology and evolutionary history of these viruses. Furthermore, this knowledge is important for conservation and captive management of lemurs.

Inhibition of HIV-1 infection by human pegivirus type 1-derived peptides is affected by human pegivirus type 1 genotype and HIV-1 coreceptor tropism.

OBJECTIVE(S): Up to 40% of HIV-1 infected individuals are coinfected with human pegivirus type 1 (HPgV-1). The majority of studies, but not all, have reported a beneficial effect of HPgV-1 coinfection on HIV-1 disease progression. So far, the impact of different HPgV-1 genotypes on different HIV-1 subtypes remains unclear. METHODS: Peptides derived from HPgV-1 envelope protein E2, and representing different viral genotypes, were synthesized using Fmoc/t-Bu-based solid phase peptide synthesis. The inhibitory effect of these peptides on the infection of reporter cell lines was tested using an HIV-1 subtype panel representing clades A (n = 2), AG (n = 2), B (n = 6), C (n = 2), D (n = 2), F (n = 2), G (n = 1), G/H (n = 1), and group O (n = 2). RESULTS: HIV-1 infection was blocked more efficiently by peptides derived from HPgV-1 GT2 than GT1 (P = 0.05). The HIV-1 subtype did not affect the degree of inhibition by a peptide derived from HPgV-1 GT2. All CXCR4-/dual-tropic isolates (n = 12), but only half (four out of eight) CCR5-tropic viruses were inhibited by this peptide (P = 0.014). CONCLUSION: Our data indicate that the inhibitory effect of peptides derived from HPgV-1 E2 protein is dependent on the genotype, suggesting that coinfection with HPgV-1 GT1 is less likely to confer a beneficial effect on HIV-1 disease progression than GT2. The preferential suppression of more pathogenic CXCR4-tropic HIV-1 by peptides derived from HPgV-1 GT2 may explain the favorable effect in patients harboring these HIV-1 isolates. Consequently, HPgV-1 genotype and HIV-1 coreceptor tropism are likely determinants for the beneficial effect of HPgV-1 co-infection in HIV-1-infected individuals.

Subverting the mechanisms of cell death: flavivirus manipulation of host cell responses to infection.

Viruses exploit host metabolic and defence machinery for their own replication. The flaviviruses, which include Dengue (DENV), Yellow Fever (YFV), Japanese Encephalitis (JEV), West Nile (WNV) and Zika (ZIKV) viruses, infect a broad range of hosts, cells and tissues. Flaviviruses are largely transmitted by mosquito bites and humans are usually incidental, dead-end hosts, with the notable exceptions of YFV, DENV and ZIKV. Infection by flaviviruses elicits cellular responses including cell death via necrosis, pyroptosis (involving inflammation) or apoptosis (which avoids inflammation). Flaviviruses exploit these mechanisms and subvert them to prolong viral replication. The different effects induced by DENV, WNV, JEV and ZIKV are reviewed. Host cell surface proteoglycans (PGs) bearing glycosaminoglycan (GAG) polysaccharides - heparan/chondroitin sulfate (HS/CS) - are involved in initial flavivirus attachment and during the expression of non-structural viral proteins play a role in disease aetiology. Recent work has shown that ZIKV-infected cells are protected from cell death by exogenous heparin (a GAG structurally similar to host cell surface HS), raising the possibility of further subtle involvement of HS PGs in flavivirus disease processes. The aim of this review is to synthesize information regarding DENV, WNV, JEV and ZIKV from two areas that are usually treated separately: the response of host cells to infection by flaviviruses and the involvement of cell surface GAGs in response to those infections.

Rewiring cellular networks by members of the Flaviviridae family.

Members of the Flaviviridae virus family comprise a large group of enveloped viruses with a single-strand RNA genome of positive polarity. Several genera belong to this family, including the Hepacivirus genus, of which hepatitis C virus (HCV) is the prototype member, and the Flavivirus genus, which contains both dengue virus and Zika virus. Viruses of these genera differ in many respects, such as the mode of transmission or the course of infection, which is either predominantly persistent in the case of HCV or acutely self-limiting in the case of flaviviruses. Although the fundamental replication strategy of Flaviviridae members is similar, during the past few years, important differences have been discovered, including the way in which these viruses exploit cellular resources to facilitate viral propagation. These differences might be responsible, at least in part, for the various biological properties of these viruses, thus offering the possibility to learn from comparisons. In this Review, we discuss the current understanding of how Flaviviridae viruses manipulate and usurp cellular pathways in infected cells. Specifically, we focus on comparing strategies employed by flaviviruses with those employed by hepaciviruses, and we discuss the importance of these interactions in the context of viral replication and antiviral therapies.

Breeding consequences of flavivirus infection in the collared flycatcher.

BACKGROUND: The breeding consequences of virus infections have rarely been studied in avian natural breeding populations. In this paper we investigated the links between humoral immunity following a natural flavivirus infection and reproduction in a wild bird population of collared flycatcher (Ficedula albicollis). We analyzed plasma from 744 birds for antibodies and correlated these results to a number of reproductive components. RESULTS: Nearly one third (27.8%) of the sampled collared flycatchers were found seropositive for flavivirus. Males had significantly more frequently flavivirus antibodies (32.3%) than females (25.1%). Seropositive females differed significantly from seronegative females in four traits: they had earlier lay date, higher body weight, higher survival rate and were older than seronegative females. The females did not differ in clutch size, number of fledged young or number of recruited young. Seropositive males had female partners with earlier lay date, i.e. the males bred earlier and they also produced more fledged young than seronegative males. In contrast, the males did not differ in clutch size, number of recruited young, male weight, age or survival. Interestingly, seropositive males had larger ornament, forehead badge size, than seronegative males. CONCLUSIONS: Collared flycatchers with an antibody response against flavivirus were more successful than birds with no antibody response, for any of the measured life history traits. The positive link between flavivirus antibody presence and life-history trait levels suggest that it is condition dependent in the collared flycatcher.

An "All-In-One" Pharmacophoric Architecture for the Discovery of Potential Broad-Spectrum Anti-Flavivirus Drugs.

A precipitous increase in the number of flaviviral infections has been noted over the last 5 years. Despite these outbreaks, treatment protocols for infected individuals remain ambiguous. Numerous studies have identified NITD008 as a potent flavivirus inhibitor; however, clinical testing was dismissed due to undesirable toxic effects. The binding landscape of NITD008 in complex with five detrimental flaviviruses at the RNA-dependent RNA polymerase active sites was explored. An "all-in-one" pharmacophore model was created for the design of small molecules that may inhibit a broad spectrum of flaviviruses. This pharmacophore model approach serves as a robust cornerstone, thus assisting medicinal experts in the composition of multifunctional inhibitors that will eliminate cross-resistance and toxicity and enhance patient adherence.

The human pegivirus: A new name for an "ancient" virus. Can transfusion medicine come up with something new?

Human pegivirus (HPgV, formerly called GB virus C/hepatitis G virus) is a poorly understood RNA virus of the Flaviviridae family. The HPgV infection is common worldwide and the virus is likely transmitted by blood products. At this time, no causal association between HPgV and human diseases has been identified. While waiting for new findings to better understand the Pegivirus genus, the aim of our narrative review is to discuss the currently available information on HPgV focusing on its prevalence in blood donors and its potential threat to transfusion safety.

Innate Immune Evasion Mediated by Flaviviridae Non-Structural Proteins.

Flaviviridae-caused diseases are a critical, emerging public health problem worldwide. Flaviviridae infections usually cause severe, acute or chronic diseases, such as liver damage and liver cancer resulting from a hepatitis C virus (HCV) infection and high fever and shock caused by yellow fever. Many researchers worldwide are investigating the mechanisms by which Flaviviridae cause severe diseases. Flaviviridae can interfere with the host's innate immunity to achieve their purpose of proliferation. For instance, dengue virus (DENV) NS2A, NS2B3, NS4A, NS4B and NS5; HCV NS2, NS3, NS3/4A, NS4B and NS5A; and West Nile virus (WNV) NS1 and NS4B proteins are involved in immune evasion. This review discusses the interplay between viral non-structural Flaviviridae proteins and relevant host proteins, which leads to the suppression of the host's innate antiviral immunity.

Diverse Viruses Require the Calcium Transporter SPCA1 for Maturation and Spread.

Respiratory and arthropod-borne viral infections are a global threat due to the lack of effective antivirals and vaccines. A potential strategy is to target host proteins required for viruses but non-essential for the host. To identify such proteins, we performed a genome-wide knockout screen in human haploid cells and identified the calcium pump SPCA1. SPCA1 is required by viruses from the Paramyxoviridae, Flaviviridae, and Togaviridae families, including measles, dengue, West Nile, Zika, and chikungunya viruses. Calcium transport activity is required for SPCA1 to promote virus spread. SPCA1 regulates proteases within the trans-Golgi network that require calcium for their activity and are critical for virus glycoprotein maturation. Consistent with these findings, viral glycoproteins fail to mature in SPCA1-deficient cells preventing viral spread, which is evident even in cells with partial loss of SPCA1. Thus, SPCA1 is an attractive antiviral host target for a broad spectrum of established and emerging viral infections.