Maternal Antibody Transfer of a Fiber-Based Subunit Vaccine Confers Complete Protection Against Fowl Adenovirus Serotype 11 in Neonatal Chickens.

Fowl adenovirus serotype 11 (FAdV-11) is an emerging pathogen associated with inclusion body hepatitis (IBH) and high mortality in commercial broilers. In this study, we evaluated the protective efficacy of maternal antibody transfer against FAdV-11 in neonatal chicks. A hypervirulent FAdV-11 strain (FAdV-11/HB2022/1), isolated from an IBH outbreak in Hubei Province, China, caused 90% mortality in 1-day-old specific-pathogen-free (SPF) chickens; 7-day-old chicks exhibited no mortality but developed mild hepatic lesions and sustained viral replication. A soluble, trimeric Fiber subunit vaccine (Fiber282-569) was developed through rational truncation of the transmembrane domain, retaining both the shaft and head domains, with its homotrimeric conformation confirmed by size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS). Immunization of breeder hens with Fiber282-569 elicited high titers of FAdV-11-specific IgY and neutralizing antibodies that were efficiently transferred to progeny via the egg yolk. Upon lethal challenge with FAdV-11/HB2022/1, 1-day-old progeny chicks from vaccinated breeders exhibited 100% survival with no clinical signs, no gross pathological lesions, and undetectable viral loads in liver tissues, demonstrating complete protection. In contrast, all chicks from unvaccinated breeders succumbed within 5 days post-infection. These results demonstrate that maternal antibody transfer of the fiber-based subunit vaccine confers complete protection against lethal FAdV-11 infection in neonatal chicks, providing a safe and effective candidate strategy for controlling FAdV-11 in the poultry industry.