Longitudinal serological monitoring of commercial broiler breeders for fowl adenoviruses (FAdVs) – presence of antibodies is linked with virus excretion

Currently, poultry industry worldwide is facing an emerging trend of fowl adenoviruses (FAdV)-associated diseases with significant economic impact, especially in meat type chickens. Vertical transmission is an important feature of all FAdVs, hence preventive measures mostly revolve around breeding stocks. However, knowledge about temporal development of FAdV infections in modern commercial settings is rare or even not existing. In the present study, longitudinal monitoring for FAdV was conducted in broiler breeder flocks located in a confined geographical region with intensive poultry production in Iran. For this, antibody status of birds from 4 to 32 weeks of age was monitored by a commercial FAdV-ELISA and virus neutralization test (VNT). In parallel, fecal shedding of FAdV was determined at peak of egg production by real time PCR and virus isolation. Overall, the commercial ELISA showed seroconversion of flocks before onset of production. VNT resolved in detail infection patterns of individual serotypes with a primordial FAdV-D (FAdV-2/-11) infection, frequently followed by FAdV-E (FAdV-8a, -8b) superinfection. FAdV-A (FAdV-1) was traced in half of the investigated flocks while no evidence of infection with FAdV-C (FAdV-4, -10) was noted. Common serological profiles between different houses of the same farm indicate an overarching biosecurity. Serological profiles coupled with virological findings at peak of egg production indicated that higher antibody levels, determined by ELISA, correlated with lower amounts of viral DNA in fecal excretion. Simultaneously, the number of isolated FAdVs belonging to distinct serotypes declined in accordance with a rise of neutralizing antibodies in birds underlining the significance of serotype-specific antibodies in the epidemiology of FAdV in breeders. Investigations in breeders were complemented with screening of FAdV-associated diseases in local broilers over a three-year period; twenty-six cases of inclusion body hepatitis (IBH) with dominant involvement of FAdV-11/FAdV-8b, one outbreak of adenoviral gizzard erosion (AGE) related to FAdV-1, and no evidence of hepatitis-hydropericardium syndrome (HHS) suggest that identical serotypes are maintained in the local poultry industry.