Isolation, Characterization, and Seroprevalence of Serotype-1 and 4 Fowl Adenoviruses in Chickens in Taiwan

Abstract

Fowl adenoviruses (FAVs) were isolated from eight one day-old healthy broilers originated from two parent flocks. FAVs were characterized by the whole DNA genomic typing, hexon-based polymerase chain reaction combined with restriction enzyme analysis of the amplified DNA fragment, and by virus neutralization using serotype specific antisera. The isolates belonged to either DNA group A/serotype 1 (FAV-1) or DNA group C/serotype 4 (FAV-4). The pathogenicity of these isolates was studied in day-old specifio-pathogen-free (SPF) chicks. Each chick was orally inoculated with one strain of the virus at a dose of 10^3 TCID(subscript 50). FAV-4 isolates significantly decreased weight gain, whereas FAV-l isolates did 50 only when the chicks were also immunosuppressed with cyclo-phosphamide. Examination of various chicken flocks in Taiwan revealed seroprevalence rates of 58.1-60.7 % for FAV-l and 12.9-16 % for FAV-4 in broilers and hybrid broilers younger than two weeks of age. After the decline of maternal antibody, the positive rate in hybrid broiler rose again and increased from eight weeks of age onwards. In breeder chickens older than 25 weeks of age, the seroprevalence rates were 46.4% (FAV-1) and 12.1% (FAV-4).