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Mass mortality in Caspian terns (Hydroprogne caspia), Pallas’s gulls (Ichthyaetus ichthyaetus), and Caspian gulls (Larus cachinnans) was recorded on the northeastern shores of the Caspian Sea in June 2022. More than 5000 gulls and terns died due to the outbreak. The outbreak was investigated in the field, and representative numbers of samples were collected and analyzed using pathological, virological, and molecular methods. Highly pathogenic avian influenza A (H5N1) viruses were detected and isolated from samples collected from dead birds. Genetic and phylogenetic analyses indicated that the hemagglutinin (HA) genes belonged to the clade 2.3.4.4.b of the H5Nx HPAI viruses, B2 sub-lineage, and were closely related to the highly pathogenic influenza viruses, caused an outbreak in wild birds with a high mortality rate in the western part of the Caspian Sea.

In 2014, a novel Avian orthoavulavirus 16 species was described among wild birds in Korea. In 2018, after massive parallel sequencing of archival strains of Avian orthoavulaviruses, isolated in 2006 in Central Kazakhstan, isolates belonging to this serotype were detected. The obtained data allowed to trace the evolution of this serotype in Asia and to reveal its evolutionary relationships with other Avulavirinae subfamily species. It was determined that Avian orthoavulavirus 16 is phylogenetically very close to Avian orthoavulavirus 1 (Newcastle disease virus) in its genomic characteristics. It is known that Avian orthoavulavirus 1 is divided into two phylogenetically distant Classes I and II. Avian orthoavulavirus 16 turned out to be very close to lentogenic Class I, which circulates mainly among wild birds. It was suggested that Avian orthoavulaviruses 1 and 16 may have common evolutionary origin and in ecological terms, both serotypes are circulating among wild birds of the order Anseriformes (ducks and geese), but Avian orthoavulavirus 1 has gradually replaced Avian orthoavulavirus 16 from active circulation.

Three isolates APMV/gull/Kazakhstan/5976/2014, APMV/gull/Kazakhstan/ 5977/2014 and APMV/gull/Kazakhstan/5979/2014, were obtained from independent samples during annual surveillance for avian influenza and paramyxoviruses in wild birds from the Caspian Sea coast in Western Kazakhstan, and were initially identified as putative paramyxoviruses on the basis of electron microscopy. Hemagglutination Inhibition Assays with antisera to nine known APMV serotypes (APMV1-9) indicated no relation to any of them. Next generation sequencing of whole genome sequences indicated the three isolates were genetically identical, and had a nucleotide structure typical for all APMVs, consisting of six genes 3'-NP-P-M-F-HN-L-5'. Phylogenetic analyses, and assessment of amino acid identities, suggested the most closely related lineages to be APMV-2, 8, 10 and 15, but the novel isolate had less than 64% identity to them and all other known avian paramyxoviruses. This value was above levels considered to generally define other APMV serotypes. Estimates of the evolutionary divergence of the nucleotide sequences of the genomes of APMVs have shown that novel Kazakhstan APMV strain was closest to APMV-2, APMV-8, APMV-10 and APMV-15, with calculated distance values of 2.057, 2.058, 2.026 and 2.286 respectively, which is above values considered to differentiate other serotypes (observed minimum was 1.108 between APMV-1 and recently isolated APMV/UPO216/Korea). Together, the data suggest that isolate APMV/gull/Kazakhstan/5976/2014 and other two should be considered as the first representative of a novel APMV-20 group, and is the first time that avian paramyxoviruses have been found infecting members of the gull family, extending the known taxonomic host range.