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In the present study day-old specific-pathogen-free (SPF) and commercial broilers with maternally derived fowl adenovirus serotype 1 (FAdV-1) antibodies were orally infected with a European “pathogenic” FAdV-1, isolated from broilers showing signs of gizzard erosion. During the experiment, broilers were observed and weighed daily up to 17 days post infection (dpi). Clinically, both infected groups showed significant decrease of weight compared to respective negative control groups. Birds were examined by necropsy at 3, 7, 10, 14 and 17 dpi. Pathological changes in the gizzards were noticed in both experimentally infected groups from 7 dpi onwards. Macroscopically, erosion of the koilin layer and inflammation or ulceration of the gizzard mucosa were observed. Histologically, presence of FAdV-1 in intranuclear inclusion bodies of degenerated glandular epithelial cells was demonstrated by in-situ hybridization and inflammatory cell infiltration of the lamina propria, submucosa and muscle layer was detected. Tissue samples were investigated by a recently developed real-time PCR and the viral DNA load was calculated from gizzard, liver, spleen and cloacal swabs with the highest amounts of FAdV-1 DNA found in the gizzard. For the first time, successful reproduction of clinical signs in broilers as well as pathological lesions in the gizzard were achieved with a European FAdV-1 isolate displaying some genetic differences to so far reported virulent FAdV-1 from Japan. Furthermore, highest viral load in gizzards could be linked with macroscopical and histological lesions. Therefore, the conducted analyses provide important insights into the pathogenesis of adenoviral gizzard erosion.

In the present study, the classification of fowl adenoviruses (FAdVs) based on a part of the 52K gene region was described. A total of 44 FAdV field samples from different countries and sources were detected using a recently developed SYBR Green-based real-time PCR. Amplified products were sequenced, and phylogenetic analyses were conducted on the basis of the 116-bp region. For comparison, the already published sequences of the 52K gene region of aviadenoviruses were used in the analyses. The phylogenetic analysis allowed the grouping of the FAdVs into the established five different FAdV species: Fowl adenovirus A to Fowl adenovirus E. The existence of the species was supported by high bootstrap values (> 70%). This method provides the advantages of quantitation and high sensitivity for FAdV detection in combination with species assignment.

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