Currently, N2 subtype avian influenza (AI) virus actively circulates in domestic and wild bird populations and is regularly detected in China, other Asian countries and Russia, particularly in combination with H9 hemagglutinin. Therefore, a method for rapid detection of the said infectious agent is urgently required. Data on oligonucleotide primer selection and reverse transcription real-time polymerase chain reaction condition optimization for N2 AI virus detection are presented in the paper. Modified primers and probe proposed by B. Hoffmann in 2006 as well as original primers and probes with the viruses available in the Laboratory working collection and selected during testing were assessed for N2 neuraminidase gene fragment amplification. Optimal concentrations of real-time RT-PCR master mix components and temperature-time mode were determined. Various combinations of primers were tested against ten N2 avian influenza virus isolates that genetically differed from each other in N gene. Nine viruses were isolated from birds in the Russian Federation regions and classified to different genetic groups. The real-time RT-PCR assay was tested for its specificity using AI virus isolates of different neuraminidase subtypes (H5N8, H3N6, H4N6, H5N1, H10N7) as well as samples containing other RNA-viruses: Newcastle disease virus, infectious bronchitis virus and infectious bursal disease virus. As a result of the testing, real-time RT-PCR conditions providing high sensitivity and specificity of the assay were selected and optimized.

At the end of 2020, a large-scale bird death was registered at one of the poultry farms in the Astrakhan region, the cause of which was avian influenza. Data on detection of the marker substitutions in viral proteins of avian influenza virus A/chicken/Astrakhan/2171-1/2020 isolate are presented in the paper. Type A Н5N8 avian influenza virus was identified with complex PCR-based methods in the submitted samples. Hemagglutinin gene fragment sequencing identified REKRRKR/ GLF, highly pathogenic avian influenza virus isolate-characteristic amino acid sequence of the hemagglutinin cleavage site. Phylogenetic analysis of nucleotide sequences of hemagglutinin gene segment (848–1105 bp ORF) allowed A/chicken/Astrakhan/2171-1/2020 H5N8 isolate to be classified to highly pathogenic avian influenza virus genetic clade 2.3.4.4. Comparative analysis of genome segments using available databases showed that A/chicken/Astrakhan/2171-1/2020 H5N8 virus related to А/Н5 avian influenza virus isolates detected in the Russian Federation in 2016–2020. Analysis of the studied virus isolate hemagglutinin amino acid identified AIV-characteristic G225QRG228 amino acids in the receptor-binding domain of the protein enabling high-affinity binding to avian epithelial cell SAα-2,3- gal receptors. Single mutations, 70G in NEP protein and 13Р in PB1 protein, out of the list of the reported influenza virus mutations affecting successful influenza virus replication in mammals were identified. No mutations affecting virus sensitivity to anti-viral medicines, rimantadin, amantadine, oseltamivir and zanamivir, were detected. The following mutations recognized as pathogenicity determinants in mice were found: 42S in the NS1 protein and 30D protein 215A in M1 protein.

The paper presents data on the study of genetic characteristics of the infl uenza virus A/chicken/ Chelyabinsk/30/2019 H9N2 isolated from pathological material (chicken internal organs) in February 2019 and received from the poultry farm in the Chelyabinsk Oblast. The H9N2 subtype of the isolated virus was identifi ed based on virological analysis. Sequencing of the hemagglutinin gene segment revealed that the amino acid sequence at the cleavage site was RSSR/GLF, which is characteristic of a low virulent avian infl uenza virus. Phylogenetic analysis of the obtained nucleotide sequences of the hemagglutinin gene fragment (1–1539 bp open reading frame) showed that the A/chicken/Chelyabinsk/30/2019 H9N2 isolate belongs to the G1 genetic group of the low virulent infl uenza virus A/H9, the representatives of which are widely spread in the Middle Eastern and Central Asian countries. The complete nucleotide genome sequence of the studied pathogen was determined. The comparative analysis of all genomic segments using the GenBank database revealed a close relationship (over 99%) between the A/chicken/Chelyabinsk/30/2019 H9N2 virus and the A/H9 infl uenza virus isolates circulating in Israel in 2006–2012. According to the analysis of the predicted amino acid sequence of the studied isolate, the positions of some molecular markers that determine the biological properties of the virus have been identifi ed. Most amino acid positions of hemagglutinin (according to H3 subtype sequence numbering) suggest affi nity for the ACA2-3Gal-receptors of avian epithelial cells. Amino acid substitutions were detected at the site within the receptor-binding domain as compared to the A/H9N2 infl uenza virus isolates obtained in Russia in 2018. The primary structure of the A/chicken/Chelyabinsk/30/2019 H9N2 isolate demonstrates a very high level of genetic similarity to the infl uenza virus isolate A/chicken/ Israel/215/2007 H9N2 used as a vaccine strain.

The results of the scientific expedition to Tere Khol and Uvs Nuur Lakes in the Republic of Tyva with the purpose of active monitoring of highly dangerous diseases in wild migratory waterfowl and epidemic analysis of these biotope water areas are presented in the paper. The Uvs Nuur Lake is a kind of an indicator for avian influenza introduction to the Russian Federation, because this is the resting and nesting area for many migratory wild birds during the period of mass migrations from Central and South-East Asian countries. In the process of active monitoring the complete autopsy of bird carcasses with description of organs and systems and sampling for laboratory diagnostics were performed. Droppings (pooled samples), parts of internal organs from dead and shot birds, blood (if possible) served as biological and pathological material for testing. While sampling, species were identified using an ornithological guide. The autopsy of dead waterfowl and birds shot for diagnostic purposes demonstrated a high worm burden of nematodes and cestodes. Two samples from European herring gulls were positive for avian influenza type A virus genome and subtype H13N6 was identified in one of them. Avian paramyxovirus serotype 1 (APMV-1), the agent of Newcastle disease, was found in one sample from gulls. The lakes of the Republic of Tyva are the most significant sites for sampling of biological material from wild birds, as the primary detection of highly pathogenic avian influenza virus in this territory is a serious signal of potential further virus spread and a precursor to a probable epizooty. Notwithstanding the absence of AIV very virulent isolate detections in wild bird populations the middle term prognosis for 2020 can be designated as cautious, as the avian influenza epidemic situation is deteriorating globally, especially in the European countries, and the threat of the virus introduction to the Russian territory with migratory birds still exists.