Inapparent Tick-Borne Orthoflavivirus Infection in Macaca fascicularis: A Model for Antiviral Drug and Vaccine Research

Tick-borne encephalitis virus (TBEV) and Powassan virus (POWV) are neurotropic tick-borne orthoflaviviruses. They cause mostly asymptomatic infections in hosts, but severe forms with CNS involvement can occur. Studying the early stages of viral infections in humans is challenging, and appropriate animal models are essential for understanding the factors determining the disease severity and for developing emergency prophylaxis and treatment options. In this work, we assessed the model of the early stages of TBEV and POWV mono- and co-infections in Macaca fascicularis. Serological, biochemical, and virological parameters were investigated to describe the infection, including its impact on animal behavior. Viremia, neutralizing antibody dynamics, and viral load in organs were chosen as the main parameters distinguishing early-stage orthoflavivirus infection. Levels of IFNα, monocyte count, and cognitive test scores were proposed as additional informative indicators. An assessment of a tick-borne encephalitis vaccine using this model showed that it provided partial protection against POWV infection in Macaca fascicularis without signs of antibody-dependent enhancement of infection.

A systems biology approach to better understand human tick-borne diseases

Tick-borne diseases (TBDs) are a growing global health concern. Despite extensive studies, ill-defined tick-associated pathologies remain with unknown aetiologies. Human immunological responses after tick bite, and inter-individual variations of immune-response phenotypes, are not well characterised. Current reductive experimental methodologies limit our understanding of more complex tick-associated illness, which results from the interactions between the host, tick, and microbes. An unbiased, systems-level integration of clinical metadata and biological host data - obtained via transcriptomics, proteomics, and metabolomics - offers to drive the data-informed generation of testable hypotheses in TBDs. Advanced computational tools have rendered meaningful analysis of such large data sets feasible. This review highlights the advantages of integrative system biology approaches as essential for understanding the complex pathobiology of TBDs.

Facilitating Antiviral Drug Discovery Using Genetic and Evolutionary Knowledge

Over the course of human history, billions of people worldwide have been infected by various viruses. Despite rapid progress in the development of biomedical techniques, it is still a significant challenge to find promising new antiviral targets and drugs. In the past, antiviral drugs mainly targeted viral proteins when they were used as part of treatment strategies. Since the virus mutation rate is much faster than that of the host, such drugs feature drug resistance and narrow-spectrum antiviral problems. Therefore, the targeting of host molecules has gradually become an important area of research for the development of antiviral drugs. In recent years, rapid advances in high-throughput sequencing techniques have enabled numerous genetic studies (such as genome-wide association studies (GWAS), clustered regularly interspersed short palindromic repeats (CRISPR) screening, etc.) for human diseases, providing valuable genetic and evolutionary resources. Furthermore, it has been revealed that successful drug targets exhibit similar genetic and evolutionary features, which are of great value in identifying promising drug targets and discovering new drugs. Considering these developments, in this article the authors propose a host-targeted antiviral drug discovery strategy based on knowledge of genetics and evolution. We first comprehensively summarized the genetic, subcellular location, and evolutionary features of the human genes that have been successfully used as antiviral targets. Next, the summarized features were used to screen novel druggable antiviral targets and to find potential antiviral drugs, in an attempt to promote the discovery of new antiviral drugs.

Single nucleotide polymorphism rs110861313 in the intergenic region of chromosome 23 is associated with the development of leukosis in the Russian Black Pied cattle

In recent years, using a genome-wide association study (GWAS), a number of single nucleotide polymorphisms (SNPs) have been suggested to be associated with susceptibility to leukemia in cattle. However, all studies have been done with purebred Holstein cows and their hybrids. In this regard, it is important to confirm the functional role of polymorphisms previously identified in a GWAS study in Russian cattle breeds. The aim of this study was to verify the association between rs110861313 in the intergenic region of bovine chromosome 23 and leukemia in the Russian Black Pied cattle. Based on the levels of bovine leukemia virus (BLV)-specific antibodies detected in serum using serodiagnostic techniques, animals were divided into three groups: healthy animals (n = 115), asymptomatic virus carriers (n = 145) and animals with leukemia (n = 107). Genotyping of rs110861313 was carried out using polymerase chain reaction followed by analysis of restriction fragment length polymorphisms. A significant decrease in the frequency of the A/A genotype (11.2 %) was revealed in animals with persistent lymphocytosis compared to virus carriers (27.6 %) (p < 0.002). At the same time, the frequency of animals with the C/C genotype in animals with persistent lymphocytosis (41.1 %) was significantly higher than that of virus carriers (21.4 %) (p < 0.001). In this case, asymptomatic virus carriers can be considered a more suitable control than healthy animals that have not been in contact with the virus. According to bioinformatics analysis, resistance to BLV can be due to the presence of the transcription factor FOXM1 binding site in the region of rs110861313. FOXM1 is expressed in immune cells and can potentially affect the expression of the neighboring genes (LY6G5B, GPANK1, ABHD16A, LY6G6F, LY6G6E, CSNK2B, ApoM). Thus, we found that SNP rs110861313 in the intergenic region of bovine chromosome 23 is associated with the development of leukemia following BLV infection in the Russian Black Pied cattle.

Ixodid ticks and tick-borne encephalitis virus prevalence in the South Asian part of Russia (Republic of Tuva)

The most significant processes of arbovirus evolution can be expected to occur in the territories where ticks of different species cohabitate and at the boundaries of virus occurrence, where the probability of the appearance of new virus variants is high due to the possible shift in the main vectors and/or vertebrate hosts. One of the most interesting regions in this regard is the Republic of Tuva. Since most of its territory is covered by mountain ranges and intermountain basins, we were able to study the distribution of vectors and viruses in geographically isolated areas at different altitudes and in various landscapes. From 2008 to 2017, we conducted six expeditions to Tuva and collected 3,077 adult ticks and 24 nymphs. The distribution of tick species was confined to specific landscapes, as follows: Dermacentor nuttalli occurred in steppes, D. silvarum inhabited forest-steppe areas, and Ixodes persulcatus inhabited mixed forests. All three species of ticks were collected on plains and mountain slopes. The range of D. silvarum was shown to be lower than 1300 m above sea level (a.s.l.). Only D. nuttalli and I. persulcatus were collected at higher altitudes. According to our observations, single nymphs of D. nuttalli appear on animals one month before larvae appear. This finding confirms the hypothesis that the immature forms of D. nuttalli are able to overwinter under favourable conditions. We isolated 9 strains and 3 isolates of tick-borne encephalitis virus (TBEV) from I. persulcatus, one strain from D. nuttalli and one strain from D. silvarum. The TBEV strain from D. nuttalli was isolated from the territory inhabited only by Dermacentor ticks. All isolated strains belong to the Siberian subtype of TBEV. TBEV was detected in ticks from all the investigated altitudes. There were no statistically significant differences in the virus prevalence between the Dermacentor and Ixodes ticks. The results of our work provide additional support for the hypothesis of the existence of TBEV foci in areas with an absolute dominance of D. nuttalli.

ASSOCIATION BETWEEN POLYMORPHISMS IN GENES ENCODING 2′-5′-OLIGOADENYLATE SYNTHETASES AND THE HUMORAL IMMUNE RESPONSE UPON VACCINATION AGAINST TICK-BORNE ENCEPHALITIS

Vaccination forms active immunity and represents an effective way of preventing tick-borne encephalitis (TBE). However, excessive vaccination is unjustified in terms of economics and medical ethics. One of the individualized approaches to vaccines is the selection of vaccine doses depending on the expected levels of immune response. Therefore, there is a need for new methods for assessing potential human immune responses prior to vaccination. The aim of this study was to determine possible association between single nucleotide polymorphisms (SNPs) located within OAS2 and OAS3 genes, which have been previously associated with the development of severe forms of TBE, and the formation of antibodies and cytokines upon vaccination against TBE. The study involved 97 volunteers of both sexes who had not previously been vaccinated against TBE and had no contact with ticks. Venous blood samples were collected one month after vaccination against TBE using the EnceVir vaccine. Levels of specific IgG antibodies against tick-borne encephalitis virus and interleukin 4 (IL-4) were analyzed. Genomic DNA samples were genotyped for the SNPs rs2285932, rs2072136, rs1293762, rs15895 and rs1732778 in genes encoding 2’-5’-oligoadenylate synthetases OAS2 and OAS3. Antibody production in response to vaccine administration was significantly associated with SNP rs1732778 in the regulatory region of the OAS2 gene. This indicator was significantly higher in people with heterozygous genotypes G/A as compared to people with homozygous genotypes G/G and A/A. Carriers of the A allele (G/A or A/A genotypes) of the same SNP had reduced IL-4 levels as compared to the homozygous G/G individuals. Thus, the data obtained indicate that SNP rs1732778 in the regulatory region of the OAS2 gene correlates with the formation of antiviral IgG antibodies and changes in IL-4 levels upon vaccination. Evidently, the genetic polymorphism in OAS2 gene should be considered when performing individualized TBE vaccinations.

A database of human genes and a gene network involved in response to tick-borne encephalitis virus infection

BACKGROUND

Tick-borne encephalitis is caused by the neurotropic, positive-sense RNA virus, tick-borne encephalitis virus (TBEV). TBEV infection can lead to a variety of clinical manifestations ranging from slight fever to severe neurological illness. Very little is known about genetic factors predisposing to severe forms of disease caused by TBEV. The aims of the study were to compile a catalog of human genes involved in response to TBEV infection and to rank genes from the catalog based on the number of neighbors in the network of pairwise interactions involving these genes and TBEV RNA or proteins.

RESULTS

Based on manual review and curation of scientific publications a catalog comprising 140 human genes involved in response to TBEV infection was developed. To provide access to data on all genes, the TBEVhostDB web resource ( http://icg.nsc.ru/TBEVHostDB/ ) was created. We reconstructed a network formed by pairwise interactions between TBEV virion itself, viral RNA and viral proteins and 140 genes/proteins from TBEVHostDB. Genes were ranked according to the number of interactions in the network. Two genes/proteins (CCR5 and IFNAR1) that had maximal number of interactions were revealed. It was found that the subnetworks formed by CCR5 and IFNAR1 and their neighbors were a fragments of two key pathways functioning during the course of tick-borne encephalitis: (1) the attenuation of interferon-I signaling pathway by the TBEV NS5 protein that targeted peptidase D; (2) proinflammation and tissue damage pathway triggered by chemokine receptor CCR5 interacting with CD4, CCL3, CCL4, CCL2. Among nine genes associated with severe forms of TBEV infection, three genes/proteins (CCR5, IL10, ARID1B) were found to have protein-protein interactions within the network, and two genes/proteins (IFNL3 and the IL10, that was just mentioned) were up- or down-regulated in response to TBEV infection. Based on this finding, potential mechanisms for participation of CCR5, IL10, ARID1B, and IFNL3 in the host response to TBEV infection were suggested.

CONCLUSIONS

A database comprising 140 human genes involved in response to TBEV infection was compiled and the TBEVHostDB web resource, providing access to all genes was created. This is the first effort of integrating and unifying data on genetic factors that may predispose to severe forms of diseases caused by TBEV. The TBEVHostDB could potentially be used for assessment of risk factors for severe forms of tick-borne encephalitis and for the design of personalized pharmacological strategies for the treatment of TBEV infection.