Fowl adenovirus serotype 1 detection in broilers: gizzard erosion pattern characterization and confirmation by FISH and PCR

ABSTRACT: Adenoviral gizzard erosions have been affecting domestic and wild birds worldwide, highlighting the need for new diagnostic approaches. Therefore, this study aimed to identify and score gizzard lesions caused by fowl adenovirus serotype 1 (FAdV-1) in chickens of different ages from commercial farms located in two states of the South and Central-West regions of Brazil, as well as to apply the fluorescent in situ hybridization (FISH) technique as a diagnostic tool. A total of 56 samples were collected from broilers aged between 1 and 45 days, showing poor performance and suspected gizzard erosion or ulceration. Samples were analyzed macroscopically and histologically, and the presence of the agent was confirmed by polymerase chain reaction (PCR) and FISH techniques. Macroscopically, only 5.35% of the gizzards presented lesions, classified as grades 1 and 2, corresponding to Group 1 (66.67%) and Group 2 (33.33%), respectively. The lesions were focal to multifocal, whitish, and resembled the detachment of the koilin membrane, measuring approximately 0.4 cm in diameter. Histologically, 92.85% of the analyzed samples showed alterations: 9.61% presented only koilin membrane rarefaction (grade 1), 50% exhibited lymphocytic and granulocytic ventriculitis with fragmentation or erosion of the koilin layer (grade 2), and 40.38% showed fibrosis associated with ventriculitis and erosion of the koilin layer. Intranuclear inclusion bodies were also observed in 26.78% of the samples. Positive signals for FAdV-1 were detected in 57.14% and 30.35% of the samples analyzed by FISH and PCR, respectively. Broilers aged one to two weeks exhibited acute lesions, while those aged three weeks or older presented chronic lesions. The chronicity of the lesions, associated with lower viral load in the tissues of broilers older than three weeks, negatively influenced the PCR results. In conclusion, different degrees of gizzard erosion were identified in chickens of various ages in Brazil. The FISH technique can be used as a diagnostic method for the detection of FAdV-1 in gizzard tissues.