Prevalence and characteristics of a novel bovine adenovirus type 3 with a natural deletion fiber gene.

Bovine adenovirus type 3 (BAdV-3) is an important pathogen causing bovine respiratory disease complex (BRDC). From Jun 2016 to Jun 2018, 108 nose swab samples were collected from cattle with BRDC from 11 farms in five cities, and 78.7% (85/108) samples were detected as BAdV-3 positive by Real-time PCR. Interestingly, the sequences of 7/10 fiber (852 bp) and hexon (785 bp) fragments cloned from 10 positive samples from eight farms were clustered into a single branch of the evolutionary tree. A BAdV-3 strain (BO/YB24/17/CH) was successfully isolated. The isolate caused pathological changes of lung, trachea and spleen in BALB/c mice. Notably, 79 amino acid deletions in the shaft domain and 74 unique amino acid mutations were found in the fiber gene of the isolate compared with the available complete sequences for fiber genes in the GenBank database. These characteristics indicated that the isolate may represent a novel fiber genotype of BAdV-3. A pair of specific primers covering the deletion region in the fiber gene was designed to screen the prevalence of BAdV-3 encoding the novel fiber gene. The results showed that 7 of the 10 strains possessed the novel fiber gene, and these novel fiber strains were detected from six farms in which calves were just imported from five provinces, indicating that this BAdV-3 with the natural deletion fiber gene has a wide geographical distribution in China. In conclusion, our results reveal that BAdV-3 is widespread in China and a pathogenic BAdV-3 strain with a novel fiber gene has been detected at high frequency, which is beneficial to understand the prevalence and genetic evolution of BAdV-3.