Outbreak of hepatitis-hydropericardium syndrome in blue-breasted quail (Excalfactoria chinensis) reveals a novel cross-species transmission of fowl adenovirus serotype 4

The hepatitis-hydropericardium syndrome (HHS) caused by fowl adenovirus serotype 4 (FAdV-4) is a serious avian disease associated with huge losses to poultry industry worldwide. Herein, we have demonstrated the first outbreak of HHS in blue-breasted quail (Excalfactoria chinensis). The causative agent, designated as HNSQ2023, was isolated and characterized as an FAdV-4 epidemic strain by PCR amplification, DNA sequencing and IFA staining. The comparative genomic analysis based on the viral genomes of 79 non-pathogenic or virulent FAdV-4 strains has shown that the gene order and shared open reading frames of HNSQ2023 were similar to those of previously reported virulent FAdV-4 strains. It also contains nearly 100% conserved amino-acid mutations in major structural proteins such as hexon, fiber-1 and fiber-2 similar to the virulent FAdV-4 strains, except for an irregular mutation aa46 (A to T) in fiber-1. Notably, the newly identified HNSQ2023 from Excalfactoria chinensis, and other five epidemic FAdV-4 viruses isolated separately from peacocks, chickens, ducks or pigeons during 2018-2023 have formed a closely evolutionary sub-branch, distinct from the main branch composed of the vast majority of Chinese FAdV-4 strains originated from chickens. Furthermore, animal experiments demonstrated that HNSQ2023 retained highly pathogenicity to chickens and Excalfactoria chinensis, with a same 100% morbidity and over 90% mortality in both species. Our data have shed new light on the high risk of cross-species transmission of FAdV-4 in domestic poultry and ornamental pet birds, stressing the great importance of stricter biosecurity measures and necessary vaccinations for future control of disease.