The first complete genome sequence of a highly pathogenic fowl adenovirus serotype 4 isolate from an infected chicken in Pakistan reveals the absence of a natural large genomic deletion.

Here, we present the complete genome sequence of a highly pathogenic fowl adenovirus serotype 4 (FAdV-4) isolate (PK-1-SBL2021), collected in 2021, from an infected chicken in Pakistan. Analysis of the genome sequence revealed that PK-1-SBL2021 is closely related to highly pathogenic FAdV-4 isolates from neighboring countries (China and Iran). However, the genome is devoid of a large (1966 bp) deletion commonly found in highly pathogenic FAdV-4 isolates from neighboring countries (China and Iran). Other features of the genome, such as distinct amino acid substitutions in specific proteins encoded by the genome and repeat sequences, are similar to those found in highly pathogenic FAdV-4 isolates. To the best of our knowledge, PK-1-SBL2021 represents the first highly pathogenic FAdV-4 isolate identified in the region that lacks a 1966 bp deletion in its genome. Our sequence analysis reveals that the deletion is also lacking in the genomes of multiple pathogenic FAdV-4 isolates from Pakistan, suggesting that the genomic deletion is dispensable for increased virulence of FAdV-4.