Serum as an alternative matrix for reliable molecular diagnosis of fowl adenovirus infections

Résumé

Fowl aviadenoviruses (FAdVs) are major pathogens of poultry and are associated with economically important diseases highlighting the need for reliable molecular diagnostic and practical sample matrices suitable for routine diagnosis and large-scale surveillance. In this study, we developed a universal real-time PCR assay targeting a conserved region of the FAdV penton gene and evaluated serum as a reliable matrix for molecular diagnosis. The penton-based real-time PCR assay exhibited excellent analytical performance, showing strong linearity over a wide dynamic range (10 2 –10 6 copies/μL), a high amplification efficiency of 97%, and a limit of detection of 5 copies/μL. The inter-specificity of the assay was evaluated using Avian Influenza Virus (AIV), Newcastle Disease Virus (NDV), Infectious Bronchitis Virus (IBV), and Infectious Laryngotracheitis Virus (ILTV). Clinical performance was assessed by quantitative comparison with a reference universal real-time PCR assay targeting the 52 K gene. Analysis of 56 field samples representing four circulating FAdV serotypes revealed excellent agreement between the two assays (R 2 = 0.9762). The diagnostic performance of serum was further investigated using 320 experimental samples collected from chickens experimentally inoculated with FAdV-1 and FAdV-8a and monitored over a 30-day period. Serum, gizzard, liver, and cloacal swab samples were collected longitudinally, and viral loads were quantified in each matrix. Group-based correlation analyses revealed distinct, biologically consistent patterns depending on the infecting serotype. In groups infected with FAdV-1, serum viral loads showed strong correlations with gizzard samples. In contrast, in the FAdV-8a infected group, elevated viral loads were observed in both liver and gizzard samples, highlighting the dual hepatic and gastrointestinal tropism and the higher pathogenicity of this serotype. Temporal analyses further demonstrated a progressive redistribution of viral loads, characterized by declining hepatic viral loads and increasing viral detection in serum and cloacal swabs at later stages of infection, indicating systemic dissemination.

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