Epidemiological survey of avian adenovirus in China from 2015 to 2021 and the genetic variability of highly pathogenic Fadv-4 isolates

The prevalence of poultry adenovirus in China is determined using clinical diagnosis, molecular biological testing, serological testing, and LMH cell virus isolation. These methods can track and test key poultry and waterfowl breeding areas across the country. From 2015 to 2021, 9613 suspected adenovirus samples were collected from 28 provinces. After the first generation of gene sequencing, a total of 2210 hexo gene fragments were obtained. Among them, FAdV-1 type accounted for 7.65%, FAdV-2 type accounted for 5.34%, FAdV-3 type accounted for 2.04%, FAdV-4 type accounted for 38.24%, FAdV-5 type accounted for 2.17%, FAdV-6 type accounted for 0.32%, FAdV-7 type accounted for 0.77%, FAdV-8a type accounted for 10.63%, FAdV-8b type accounted for 11.58%, FAdV-9 type accounted for 0.50%, FAdV-10 type accounted for 8.10%, and FAdV-11 type accounted for 12.67%. A total of 877 FAdV strains were isolated from FAdV suspected samples by seeding LMH cells, and there were 475 FAdV-4 strains among them. A total of 473 isolates were highly pathogenic FAdV-4, and the percentage of amino acid homology with the highly pathogenic FAdV-4 reference strains was >99.1%. Two isolates were non-pathogenic, and the amino acid homology with the ON1 reference strain was >99.6%. Part of the amino acid positions of the hexon gene have mutations, including positions 188, 193, 195, 238, and 240.