Identification and genetic evolutionary analysis of goose circovirus in Shandong and neighboring provinces in China in 2024

Goose circovirus (GoCV), a significant pathogen impacting waterfowl health, has led to significant economic losses in the goose industry. Since it was first identified in Germany in 1999, it has spread globally. To investigate the prevalence, genetic characteristics, and variation patterns of GoCV in Shandong and its neighboring provinces in China, this study used PCR to screen GoCV-positive samples collected from diseased geese in Shandong, Hebei, Henan, and Anhui provinces. Ten positive samples were selected for whole-genome amplification and sequencing. The results revealed that the nucleotide sequence homologies of the entire genome, the Rep gene, and the Cap gene of the 10 GoCV strains varied in the ranges of 96.9–99.5%, 96.6–99.7%, and 96.8–99.3%, respectively; furthermore, the amino acid sequence homologies were observed to fall in the ranges of 94.4–99.3%, 99.3–100%, and 98.0–100%, respectively. The 10 GoCV isolates showed high homology with reference strains from Anhui, Shandong, Henan, and Zhejiang provinces, relatively low homology with reference strains from Heilongjiang and Guangdong, and low homology with three duck circovirus (DuCV) reference strains. The genetic evolution tree analysis showed that nine GoCVs were clustered within the GoCV-Ⅰa branch, while one was classified into the GoCV-Ⅰb branch. Notably, these branches were clearly distinct from those of the three DuCVs, indicating a distant phylogenetic relationship between GoCV and DuCV. The results of the amino acid sequence analysis showed that compared with the first GoCV isolate from the Chinese mainland, AY633653.1 yk1, the Rep and Cap proteins had mutations at the amino acid sites 4, 5, 47, 71 and 8, 26, 49, 59, 61, 74, 76, 78, 176, 186, respectively. The results of the three-dimensional structure prediction analysis showed that these proteins had high similarity in their overall configuration, but there were certain differences in some local regions. The data indicate that GoCV is present in parts of Shandong and its neighboring provinces. The Rep protein exhibits a high degree of conservatism, whereas the Cap protein demonstrates a high mutation rate. Local structural differences may influence viral virulence and immune escape capability; finally, GoCV is genetically distinct from DuCV. Continual monitoring and analysis of mutation trends in the virus are essential, as they play a critical role in the early prevention and control of goose circovirus disease.