Vertical transmission of avian poliomavirus during natural infection

Polyomavirus causes infections worldwide in both mammals and birds. Avian Polyomaviruses (APVs) lead to diseases in geese and pet birds, which are particularly severe in young and nestling birds. Adult birds often carry persistent infections, shedding the virus through feather dust, skin exfoliation, secretions, and excretions, thereby exposing young birds to infection. Due to limited data, this study aims to investigate whether vertical transmission of APV occurs in natural infections. Thirty-eight unhatched eggs were collected from a flock of infected finches, which showed infertility, a decrease in eggs, and embryo mortality. APV was detected in 21 out of 38 eggs (55.3 %), with no difference in infection rates between finch species. Complete genome sequencing identified Finch polyomavirus with 99.7 % similarity. The viral DNA copy number in embryonated eggs ranged from 3.11 × 10^² to 1.1 × 10^⁹. In non-embryonated eggs, APV was more frequently found in the yolk than in the albumen, with DNA copy numbers ranging from 7.88 × 10^¹ to 7.91 × 10^⁵. These results suggest that vertical transmission of APV, a mode that could significantly influence the epidemiology of the infection, is possible, especially since persistent infections are common in adult birds. Furthermore, the high DNA copy number observed in some embryonic livers indicates that APV may replicate within embryonated eggs. However, it remains unclear whether the infection caused the infertility and embryo mortality.