Outbreak of FAdV-4 infection in blue-breasted quail (Excalfactoria chinensis) reveals novel cross-species transmission of virus in domestic poultry and ornamental pet birds.

Hepatitis caused by fowl adenovirus serotype 4 (FAdV-4) is a serious avian disease associated with huge losses to the poultry industry worldwide. Herein, we document the first outbreak of FAdV-4 infection in blue-breasted quail (Excalfactoria chinensis). The causative agent, designated as HNSQ2023, was isolated and characterized as an FAdV-4 epidemic strain using PCR amplification, DNA sequencing, and IFA staining. Comparative genomic analysis of the viral genomes of 79 virulent or non-pathogenic FAdV-4 strains showed 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 100% conserved amino acid mutations in major structural proteins such as hexon and fiber-2. This is similar to the virulent FAdV-4 strains, except for an irregular mutation at aa46 (A to T) in fiber-1. Notably, the newly identified HNSQ2023 isolated from Excalfactoria chinensis and the other five epidemic FAdV-4 strains previously isolated from peacocks, chickens, ducks, and pigeons during 2018-2023 formed a close evolutionary sub-branch, distinct from the main branch, mostly composed of Chinese FAdV-4 strains originating from chickens. Furthermore, animal experiments demonstrated that HNSQ2023 retained high pathogenicity to SPF chickens and Excalfactoria chinensis, with 100% morbidity and over 90% mortality in both species. Our data shed new light on the high risk of cross-species transmission of FAdV-4 in domestic poultry and ornamental pet birds, stressing the importance of stricter biosecurity measures and necessary vaccinations for future control of this disease.