[Results of investigation of ticks in Volga river delta (Astrakhan region, 2017) for Crimean-Congo hemorrhagic fever virus (Nairoviridae, Orthonairovirus, CCHFV) and other tick-borne arboviruses.]

INTRODUCTION: There are natural foci of Crimean-Congo hemorrhagic fever (CCHF) that vectored by Hyalomma marginatum ticks in Volga river delta (Astrakhan region, South of Russia). The circulation of Dhori virus (DHOV) (Thogotovirus: Orthomyxoviridae) has been also shown here. We hypothesized that other tick-borne arboviruses are also likely to circulate in the region. In particular, Bhanja virus (Phlebovirus: Phenuiviridae), Wad Medani virus (Orbivirus: Reoviridae), and Tamdy virus (Orthonairovirus: Nairoviridae), which were found to circulate in neighboring regions and are vectored by Haemaphysalis spp., Dermacenter spp., and Hyalomma spp. ticks. OBJECTIVES: The aim of the study was to examine ixodid ticks in Volga river delta for the presence of CCHFV, DHOV, Bhanja virus, Wad Medani virus, and Tamdy virus. MATERIAL AND METHODS: Ticks were collected in Volga river delta in 2017. We used molecular genetic methods for the detection and analysis of nucleic acids (PCR, sequencing, phylogenetic analysis). RESULTS: We detect CCHFV and DHOV RNA in H. marginatum ticks. The rate of infected H. marginatum ticks was 1.98% for CCHFV and 0.4% for DHOV. The results of genetic analysis showed that found DHOV strains are almost identical (99-100% in the M gene) and forms a separate genetic lineage alongside of Batken virus from Central Asia. At the same time, Bhanja virus, Wad Medani virus, and Tamdy virus were not found in ticks, collected in this region. CONCLUSIONS: DHOV is circulating in the natural foci of CCHF in the Volga river delta. The ratio of infection of H. marginatum with CCHFV and DHOV was determined for the first time.

Genetic diversity of viruses of Chenuda virus species (Orbivirus, Reoviridae) circulating in Central Asia.

Chenuda virus (CNUV) (Orbivirus, Reoviridae) is the only known orbivirus associated with argas (Argasidae) ticks. Scientific study of this group is necessary for understanding of Orbivirus genus evolution patterns. We conducted a comparative analysis of full genomes of five different viruses of Chenuda virus species, including Baku virus strains (BAKV) circulating in a rather limited area in the Central Asia and Transcaucasia. It was shown that VP4(OC1) and VP6(Hel) proteins variability greatly exceeds the variability of other proteins. The divergence between CNUV and BAKV in this proteins is about 50%. Even in closely related strains isolated from the same geographical region, the conservative genes of which are 90-95% identical, the VP4(OC1) and VP6(Hel) divergence reaches values that would usually be indicative of different serotypes (74.1-82.2%).

[Complete genome analysis of the Batai virus (BATV) and the new Anadyr virus (ANADV) of the Bunyamwera group (Bunyaviridae, Orthobunyavirus) isolated in Russia].

Almost complete nucleotide sequences for the S, M, and L segments were obtained for three strains of the Batai virus (Bunyamwera serogroup, genus Orthobunyavirus, Bunyaviridae family). Based on the results of the phylogenetic analysis conducted forthe three genomic segments LEIV Ast507 and LEIV-Ast528 strains were grouped with other European BATV isolates and were found to be almost identical to the strain 42 isolated from Volgograd Region, Russia, 2003. Surprisingly, LEIV-13395 strain isolated from the Aedes sp. mosquitos in Magadan Oblast, 1987, turned out to be a novel genotype inside Bunyamwera serogroup. The highest nucleotide identity levels of LEIV-13395 genomicsegments (86.9%, 80.8%, 79.7% for S, M and L segments respectively) were observed with corresponding segments of the Batai virus.

Deviation from the random distribution pattern of influenza A virus gene segments in reassortants produced under non-selective conditions.

High-frequency reassortment of gene segments is characteristic for influenza viruses, and it is considered to be of significance for the origin of pandemic influenza. In order to analyze whether the segregation of genes in the reassortants is random, or it deviates from the random pattern, we inoculated embryonated chicken eggs simultaneously with two influenza viruses, A/WSN/33 (H1N1) and A/Duck/ Czechoslovakia/56 (H4N6), at a high multiplicity of infection. The virus yield was used for plaque cloning, and the genetic content of plaque isolates was determined by analysis of the mobility of virus-induced proteins in polyacrylamide gel (for NP and NS genes), partial sequencing (for M gene) and polymerase chain reaction analysis with strain-specific primers for the other genes. Out of 37 isolates, 27 were reassortants. The majority of the reassortants contained the HA gene of A/WSN/33 (H1N1) virus and the NP gene of A/Duck/Czechoslovakia/56 (H4N6) virus. The data demonstrate the previously unrecognized phenomenon of segment-specific deviation from the random distribution of parent genes in the reassortants. The results are discussed in connection with the problem of differential competition between influenza A virus gene segments in mixed infection and random versus non-random reassortment of gene segments under non-selective conditions.

Immunization with influenza A NP-expressing vaccinia virus recombinant protects mice against experimental infection with human and avian influenza viruses.

Two-fold immunization of Balb/c mice with a vaccinia virus recombinant expressing the NP protein of influenza A/PR8/34 (H1N1) virus under the control of a strong synthetic promoter induced specific antibodies and protected animals against low-dose challenge by mouse-adapted heterosubtypic variants of human A/Aichi2/68 (H3N2) and avian A/Mallard/Pennsylvania/10218/84 (H5N2) influenza virus strains. The surviving immunized animals had lower anti-hemagglutinin antibody titers compared to non-immunized mice. There was no difference in viral titers in lungs of immunized and non-immunized animals that succumbed to the infection. In order to try to increase immune system presentation of NP-protein-derived peptides, and thereby increase their immunogenicity, we constructed another vaccinia-based NP-expressing recombinant containing a rapid proteolysis signal covalently bound to the NP protein. This sequence, derived from the mouse ornithine decarboxylase gene has been shown to increase degradation of various proteins. However, we found that when used as part of a recombinant NP, this signal neither increased its proteolytic degradation, nor was it more efficient in the induction of a protective response against influenza infection.

Characterization of adaptation of an avian influenza A (H5N2) virus to a mammalian host.

We have used the mouse model to monitor the acquisition of virulence of a non-pathogenic influenza A virus upon adaptation to a new mammalian host. An avian strain, A/Mallard duck/Pennsylvania/10218/84 (H5N2) (Mld/PA/84) was adapted to mice by 23 serial lung-to-lung passages until a highly virulent mouse-adapted (MA) variant (Mld/PA/84-MA) emerged. This MA variant was characterized and compared to the parental strain as well as some of its intermediate passage variants. MA variant caused bronchopneumonia in mice with a high mortality rate (the virulence of Mld/PA/84-MA measured as log (EID50/LD50) was 1.75), while the parental, avirulent strain Mld/PA/84 did not cause illness and mortality in mice (log (EID50/LD50) was 7.25). Hemagglutination-inhibition (HAI) test with a set of hemagglutinin- (HA) specific monoclonal antibodies (MAbs) revealed antigenic differences between the parental strain and MA variant. Mld/PA/84-MA reacted with HA-specific MAbs in higher titers than the parental strain. The HA genes of the parental strain Mld/PA/84, the 1st, 3rd, 8th, and 15th intermediate passage variants, and Mld/PA/84-MA were sequenced. Three amino acid changes at positions 203, 273 and 320 were determined in the HA of MA variant. The first of them, Leu-->Pro (320), appeared in the HA stem region at the 8th passage. Two other in the HA1 globular region (Ser-->Phe (203) and Glu-->Gly (273)) appeared at the 15th passage. All of these substitutions were associated with the increase of viral infectivity for mouse lungs and changes in the HA antigenicity. The potential role of these changes in HA with respect to the process of viral interspecies transmission and acquisition of virulence for new host is discussed.

Prevention and treatment of bronchopneumonia in mice caused by mouse-adapted variant of avian H5N2 influenza A virus using monoclonal antibody against conserved epitope in the HA stem region.

The effects of monoclonal antibody (MAb) C179 recognizing a conformational epitope in the middle of the hemagglutinine (HA) stem region were examined in a mouse model in the experiments of prevention and treatment of lethal bronchopneumonia caused by influenza A virus of H5 subtype. To model the lethal infection, avian nonpathogenic strain A/mallard duck/Pennsylvania/10218/84 (H5N2) was adapted to mice. This resulted in highly pathogenic pneumovirulent mouse-adapted (MA) variant, which was characterized. Three amino acid changes were found in the HA1 subunit of HA of MA virus. One of these was located inside the region of the conformational epitope recognized by MAb C179. However, this substitution was not significant for the recognition of HA and virus neutralization by MAb C179 in vitro and in vivo. Intraperitoneal administration of two different concentrations of MAb C179 one day before or two days after the virus challenge significantly decreased mortality rate. These results suggest that MAb C179 is efficient not only in the prevention and treatment of H1 and H2 influenza virus bronchopneumonia, as was reported previously, but also of H5-induced bronchopneumonia as well, and demonstrate in vivo the existence of a common neutralizing epitope in the HAs of these three subtypes.

Cross-protection and reassortment studies with avian H2 influenza viruses.

In order to assess the degree of immune cross-protection among avian H2 influenza virus strains, mice were immunised with beta-propiolactone-inactivated virus preparations and infected intranasally with mouse-adapted variant of A/Black Duck/New Jersey/1580/78 (H2N3) strain. The experiments with 11 avian H2 strains revealed that both Eurasian and American H2 avian influenza viruses exhibit either high or moderate degree of cross-protection. The grouping of the strains in accordance with their cross-protection efficiency does not coincide with H2 phylogenetic branches. Several reassortant clones were obtained with the use of A/Pintail Duck/Primorie/695/76 (H2N3) strain and high-yield X-67 reassortant as parent viruses, among them a high-yield H2N3 reassortant. Taking into account the data on cross-protection among avian H2 strains, the high-yield H2N3 reassortant may be regarded as a prototype strain to be used for the preparation of killed vaccines in the case of a new appearance of avian H2 haemagglutinin in circulation in humans.

An epitope shared by the hemagglutinins of H1, H2, H5, and H6 subtypes of influenza A virus.

The membrane-inserted hemagglutinin (HA) is the most variable protein of influenza viruses. Here we describe the characterization of a shared epitope in the HA of influenza A virus H1, H2, and H5 subtypes which were completely neutralized by a monoclonal antibody (MAb), directed against this epitope. This MAb (C179) also efficiently precipitated the HAs of these viruses. In addition, MAb C179 did not neutralize H6 subtype strains despite complete amino acid homology of the epitope regions. Furthermore, only the non-glycosylated form of the HA of one of the H6 subtype strains could be precipitated by the MAb. The conformational epitope may be masked by glycosylation, although it could not be excluded that differences in the primary amino acid sequence may cause the decreased accessibility of the epitope in H6 subtype strains.

Prevention and treatment of lethal influenza A virus bronchopneumonia in mice by monoclonal antibody against haemagglutinin stem region.

The protective properties of monoclonal antibody (MoAb) C179 directed to the stem region of haemagglutinin (HA) H2 that possessed fusion-inhibition and unique broad cross-neutralizing activities were examined in a mouse model. The MoAb efficiently protected mice against a lethal challenge with pneumovirulent human (H1) and avian (H2) strains of influenza A virus. Survival rates in mice that received intraperitonealy (i.p.) 1000 micrograms of the MoAb per mouse a day before the virus challenge were 90% for H1 and 100% for H2 strain. The dose of the MoAb of 100 micrograms per mouse significantly decreased mortality in mice. Moreover, the MoAb was also efficient in treatment of lethal bronhopneumonia caused by H2 influenza virus. The survival rate in mice that received 1000 micrograms of the MoAb per mouse 2 days after the virus challenge was 90%, while that in the control group was 30% only. These results indicate that the MoAb was effective in protection of animals against lethal influenza A infection without significant difference between H1 and H2 subtypes. The MoAb exerted significant effect in treatment of mice infected with H2 influenza virus. Thus, these data allow to suggest that the stem region of HA might be a potential target for prevention of influenza virus infection and antiviral therapy.

Differences between original strains and their mouse-adapted variants of human (H1) and avian (H2) influenza A viruses in the reaction with cross-neutralizing monoclonal antibody recognizing conformational epitope.

Human (H1) and avian (H2) influenza A viruses and their mouse-adapted (MA) variants were studied in radioimmunoprecipitation assay (RIPA) and infectivity neutralization test using a monoclonal antibody (MoAb) directed against a conserved antigenic epitope in the stem region of the haemagglutinin (HA) and reacting both with H1 and H2 subtypes of HA. Whereas the MA variant of avian influenza A virus differed from the original strain in RIPA and neutralization tests, no differences were observed between the original human strain and its MA variant, as well as between the original H1 and H2 strains.

Changes of morphological, biological and antigenic properties of avian influenza A virus haemagglutinin H2 in the course of adaptation to new host.

The alterations of avian influenza A virus haemagglutinin (HA) H2 as a result of adaptation to mice were first investigated in this study. HA of mouse-adapted (MA) variant was somewhat different from that of the original strain in electrophoretical mobility, antigenic structure and in haemagglutination activity with mouse red blood cells.

Antigenic reactivity of matrix protein and nucleoprotein of influenza virus as detected by EIA after dissociation with different detergents.

Solid phase enzyme-immunoassay (EIA) was employed to assess the antigenic reactivity of matrix protein (M) and nucleoprotein (NP) of influenza A virus adsorbed to polystyrene in the presence of different detergents such as beta-octaglucoside (OG), Triton X-100, Tween-20, sodium dodecylsulphate (SDS), sodium deoxycholate (Doch-Na), Nonidet P-40 (NP-40), and sarcosyl at concentrations ranging from 0 to 2%. The antigenic reactivity of NP was the highest in the absence of detergents. For M protein, Doch-Na, SDS, NP-40 and sarcosyl of 0.05-0.1% enhanced the chromatophoric response in EIA 1.5-2 times. In contrast, the antigenic reactivity of M protein remained unchanged after OG or Triton X-100 treatments, and it decreased in the presence of Tween-20.

Studies on the genetic basis of human influenza A virus adaptation to mice: degrees of virulence of reassortants with defined genetic content.

A highly virulent mouse-adapted variant of influenza virus A/Aichi/2/68 (H3N2) was crossed either with the original A/USSR/90/77 (H1N1) influenza virus strain or with its mouse-adapted, moderately mouse virulent variant. The reassortants were characterized with respect to their genetic content and pneumovirulence for mice. The reassortants fell into three categories: avirulent, highly virulent (resembling in this respect the parent A/Aichi/2/68 virus) and moderately virulent (resembling the mouse-adapted A/USSR/90/77 parent virus). The analysis of the parental origin of the genes of 6 reassortants allowed to suggest that changes in the HA gene and in a polymerase gene (most likely, PB1) were necessary for the acquisition of virulence by the A/USSR/90/77 virus in the course of adaptation to mice, whereas the changes in two other polymerase genes as well as in the genes NA and NS were not involved. The low degree of pathogenicity characteristic of the mouse-adapted A/USSR/90/77 virus was determined by gene(s) other than HA.

Dissociation of the haemagglutination inhibition and the infectivity neutralization in the reactions of influenza A/USSR/90/77 (H1N1) virus variants with monoclonal antibodies.

Variants of influenza A/USSR/90/77 (H1N1) virus selected with monoclonal antibody HC 142 (Res 142-1 and Res 142-2) were resistant to this antibody in a virus-neutralization (VN) test, but were inhibited in a haemagglutination-inhibition (HI) test. A variant selected with HC 22 monoclonal antibody (Res 22) was resistant to HC 142 only in VN tests. A mouse-adapted variant of A/USSR/90/77, shown previously to be resistant to HC 22, reacted with HC 142 in a manner similar to that of Res 142-1, Res 142-2 and Res 22. Another monoclonal antibody, HC 125, behaved similarly to HC 142. The addition of anti-immunoglobulin serum restored the ability of HC 142 and HC 125 (already bound to the virus) to neutralize the infectivity of the resistant variants. Polyacrylamide gel electrophoresis revealed differences in the mobility of haemagglutinin among the variants.

ELISA detection of influenza haemagglutinin depends on its molecular environment.

Two ELISA techniques (indirect and sandwich) were used for detection of influenza HA in three HA-containing specimens: whole influenza virus, HA + NA, isolated HA. Adsorptive and antigenic properties of the HA were found to depend on its physicochemical state and molecular environment.

Studies on the genetic determinants of influenza virus pathogenicity for mice with the use of reassortants between mouse-adapted and non-adapted variants of the same virus strain.

The original influenza virus strain A/USSR/90/77 (H 1 N 1) and its mouse-adapted variant, differing in their reactivity with anti-hemagglutinin monoclonal antibodies HC 22 and HC 124, were crossed in MDCK cells and in chicken embryos, and 21 clones were isolated by non-selective random cloning. In all the clones the virulence for mice was found to be linked to the antigenic specificity of hemagglutinin (HA). An independent marker, formation of filamentous forms, was reassorted with an expected frequency. In the crosses between UV-irradiated mouse-adapted variant and live non-adapted strain, with selection of clones by a mixture of monoclonal antibodies discriminating between HA of the two variants, virulence also was linked to HA gene. On the contrary, in the experiments with A/Aichi/2/68 (H 3 N 2) strain and its mouse-adapted highly virulent variant these two characteristics--virulence and HA antigenic specificity--could be dissociated. A pathogenic clone having HA of the non-adapted strain was readily obtained; its virulence, however, was weaker than that of the mouse-adapted parent. In the inter-subtypic crosses between A/USSR/90/77 and A/Aichi/2/68 the transfer of the HA gene of the mouse-adapted A/Aichi/2/68 did not confer virulence to the reassortant. The results are discussed in terms of the genetic basis of virulence acquired in the course of influenza virus adaptation to a new host.

Changes in the antigenic specificity of influenza hemagglutinin in the course of adaptation to mice.

Influenza virus strains A/USSR/90/77 (H1N1) and A/USSR/92/77 (H1N1) have been adapted to mice by successive intranasal passages. In the course of adaptation a loss (for A/USSR/90/77) or a reduction (for A/USSR/92/77) of the reactivity toward two monoclonal antibodies in a panel of seven monoclones has been registered. The changes emerged after two or three passages, long before the acquisition of the lethal effect for mice. Possible significance of the phenomenon for the antigenic variation of influenza A virus is discussed.

The role of carbohydrate in determining the immunochemical properties of the hemagglutinin of influenza A virus.

Most of the carbohydrate was removed from influenza virus MRC II (H3N2) and its purified hemagglutinin (HA) on treatment with glycosidases, including alpha-mannosidase, beta-N-acetylglucosaminidase, beta-galactosidase and alpha-fucosidase. The release of 50 per cent of the carbohydrate from intact virus particles significantly affected hemagglutinating activity. The ability of untreated and glycosidase-treated virus to inhibit the binding of antibodies directed against the hemagglutinin was almost indistinguishable by competitive radioimmunoassay (RIA). Up to 60 per cent of the carbohydrate from the purified HA of influenza virus could be removed. The antigenicity of glycosidase treated HA molecules decreased 8-fold compared to intact HAs as measured by competitive RIA. In addition, glycosidase digestion of 125I-labeled HA resulted in a decrease in its reactivity in direct RIA. We conclude that the carbohydrate portion of the HA of influenza virus is not of major importance in defining the antigenicity of HA.