Characteristics of far eastern strains of tick-borne encephalitis virus

Clinical and diagnostic manifestations of tickborne mixed infection in combination with COVID-19

The coexistence of various pathogens inside the patient's body is one of the poorly studied and current issues. The aim of the study is to identify the relationship between the indicators of complex laboratory diagnostics and the clinical manifestations of a mixed disease during subsequent infection with the SARS-CoV-2 virus using the example of a case of chronic encephalitis-borreliosis infection. Seven blood serum samples were collected from the patient over the course of a year. For the etiological verification of the causative agents of TBE, Lyme disease and COVID-19, the methods of ELISA and PCR diagnostics were used. The patient was diagnosed with Lyme disease on the basis of the detection of IgG antibodies to Borrelia 5 months after the onset of the disease, since she denied the tick bite. In the clinical picture, there was an articular syndrome and erythema migrans. Later, IgG antibodies to the TBEV were found in the blood. Throughout the study, IgM antibodies to Borrelia were not detected. The exacerbation of Lyme disease could be judged by the clinical manifestations of this disease and by the growth of specific IgG antibodies. A feature of this case was that during an exacerbation of the Lyme disease, an infection with the SARS-CoV-2 virus occurred. Treatment (umifenovir, hydroxychloroquine, azithromycin, ceftriaxone) was prescribed, which improved the condition of the underlying disease, decreased joint pain, decreased IgG levels to borrelia. However, during this period, serological markers of TBEV appear: antigen, IgM antibodies, and the titer of IgG antibodies increases. Most likely, this was facilitated by the switching of the immune system to the SARS-CoV-2 virus, with the simultaneous suppression of borrelia with antibiotics and the appointment of hydroxychloroquine, which has an immunosuppressive effect. Despite the activation of the virus, clinical manifestations of TBE were not observed in the patient, which is most likely associated with infection with a weakly virulent TBEV strain. The further course of tick-borne infections revealed the dominant influence of B. burgdorferi in relation to TBEV. Laboratory studies have shown that suppression of the activity of the borreliosis process by etiotropic treatment subsequently led to the activation of the persistent TBEV.

An mRNA Vaccine Protects Mice against Multiple Tick-Transmitted Flavivirus Infections

Powassan virus (POWV) is an emerging tick-transmitted flavivirus that circulates in North America and Russia. Up to 5% of deer ticks now test positive for POWV in certain regions of the northern United States. Although POWV infections cause life-threatening encephalitis, there is no vaccine or countermeasure available for prevention or treatment. Here, we developed a lipid nanoparticle (LNP)-encapsulated modified mRNA vaccine encoding the POWV prM and E genes and demonstrated its immunogenicity and efficacy in mice following immunization with one or two doses. The POWV mRNA vaccine induced high titers of neutralizing antibody and sterilizing immunity against lethal challenge with different POWV strains. The mRNA vaccine also induced cross-neutralizing antibodies against multiple other tick-borne flaviviruses and protected mice against the distantly related Langat virus. These data demonstrate the utility of the LNP-mRNA vaccine platform for the development of vaccines with protective activity against multiple flaviviruses.

Reverse Genetics of RNA Viruses: ISA-Based Approach to Control Viral Population Diversity without Modifying Virus Phenotype

Reverse genetic systems are essential for the study of RNA viruses. Infectious clones remain the most widely used systems to manipulate viral genomes. Recently, a new PCR-based method called ISA (infectious subgenomic amplicons) has been developed. This approach has resulted in greater genetic diversity of the viral populations than that observed using infectious clone technology. However, for some studies, generation of clonal viral populations is necessary. In this study, we used the tick-borne encephalitis virus as model to demonstrate that utilization of a very high-fidelity, DNA-dependent DNA polymerase during the PCR step of the ISA procedure gives the possibility to reduce the genetic diversity of viral populations. We also concluded that the fidelity of the polymerase is not the only factor influencing this diversity. Studying the impact of genotype modification on virus phenotype is a crucial step for the development of reverse genetic methods. Here, we also demonstrated that the utilization of different PCR polymerases did not affect the phenotype (replicative fitness in cellulo and virulence in vivo) compared to the initial ISA procedure and the use of an infectious clone. In conclusion, we provide here an approach to control the genetic diversity of RNA viruses without modifying their phenotype.

Tick-borne encephalitis virus: molecular determinants of neuropathogenesis of an emerging pathogen

Tick-borne encephalitis virus (TBEV) is a zoonotic agent causing severe encephalitis. The transmission cycle involves the virus, the Ixodes tick vector, and a vertebrate reservoir, such as small mammals (rodents, or shrews). Humans are accidentally involved in this transmission cycle. Tick-borne encephalitis (TBE) has been a growing public health problem in Europe and Asia over the past 30 years. The mechanisms involved in the development of TBE are very complex and likely multifactorial, involving both host and viral factors. The purpose of this review is to provide an overview of the current literature on TBE neuropathogenesis in the human host and to demonstrate the emergence of common themes in the molecular pathogenesis of TBE in humans. We discuss and review data on experimental study models and on both viral (molecular genetics of TBEV) and host (immune response, and genetic background) factors involved in TBE neuropathogenesis in the context of human infection.

[Phylogenetic analysis and distribution of far eastern tick-borne encephalitis virus subtype (Flaviridae, Flavirus, TBEV-FE) from Asia.]

To date, a lot of data on molecular genetic characteristics of different tick-borne encephalitis virus strains has appeared. Only on the basis of the E protein genome, sequences of about 1,500 TBEV strains were registered in GenBank.

PURPOSE

The purpose of the work - revision and comparative analysis of data on complete genomes sequences of the Far Eastern subtype of TBE virus strains distributed in the Asian part of Eurasian continent.

MATERIAL AND METHODS

The data on the complete genomes of 84 strains of TBEV isolated in Asia were used; phylogenetic analysis was performed.

RESULTS AND DISCUSSION

it was shown that variants of the TBEV of the Far Eastern subtype are circulating here and form three separate clusters (Sofjin, Senzhang- и Shkotovo-like strains). Sofjin strain (Sofjin-1953, Sofjin-Chumakov, Sofjin-KSY) was considered to be the reference for Far Eastern TBE virus subtype strains and a cluster of Sofjin-like strains. Sofjin-like strains were not found in China and Japan, but widely distributed throughout the area of Primorsky and Khabarovsk krai. The group of Senzhang-like strains was distributed in China, Eastern Siberia, Khabarovsk krai and northern Primorsky krai, but was not found in Japan (Hokkaido). According to molecular genetic characteristics the youngest and more genetically homogeneous group was the Shkotovo-like strains, isolated in the southern part of Primorsky krai, however not found on Hokkaido Island (Japan).

CONCLUSION

revision of the complete genome characteristics of TBEV strains revealed the features of micro-evolutionary process of viral populations in the Asian part of Eurasia, show the individual affection of strains to certain territories, as well as detect random finds of such strains in the territories of other natural foci.

Complete Genomic Characterization of Three Tick-Borne Encephalitis Viruses Detected Along the China-North Korea Border, 2011

Tick-borne encephalitis virus (TBEV) causes neurological infections with serious sequelae in Europe and Northeast Asia. In China, the major epidemic areas are along the borders with Russia and North Korea. Although several TBEV isolates have been reported, the biological characteristics of the Chinese strains, especially those along the China-North Korea border, are unclear. In this study, we detected seven TBEV fragment sequences in 602 adult Dermacentor silvarum collected in the Changbai Mountain area of Jilin Province on the China-North Korea border and characterized the genome of three TBEV strains (JLCB11-08, JLCB11-35, and JLCB11-40). These three TBEV strains belong to the TBEV-Far Eastern (TBEV-FE) genotype and clustered most closely with the Svetlogorie and Kavalerovo strains from Russia. In addition, the TBEV strains from Northeast China clustered geographically within the TBEV-FE subtype branch. These findings will facilitate further research on the distinct genetic groupings of TBEV strains in China.