ABSTRACT
Avian adenovirus was isolated from naturally infected birds during 1990 to 2003 in the vicinity of Karachi, Pakistan. The virus is known to cause hydro-pericardium syndrome [HPS] in poultry The mortality was recorded 20-50% in commercial broilers. Fifty field samples were collected; however, six samples were selected for molecular studies. These isolates were grown and characterized by cell culture using chicken embryo liver cell culture, chicken embryo pathogenicity, agar gel precipitation [AGP], serum neutralization test, DNA extraction, polymerase chain reaction [PCR] and restriction enzyme analysis [REA]. Reference strain J2-A [ATCC VR-829] was used to confirm that HPS isolates belongs to avian adenovirus type-4. The disease was reproduced in 28-day-old broilers by intramuscular inoculation of cell extracts. Typical hydropericardium was observed in experimental chickens 72 h post-inoculation. The 50% neutralization endpoint of pooled sera of these isolates was not recorded more than 1:40. The results showed that there was no difference in PCR product of 1319 bp with H3/H4 primer on agarose gels, which is characteristic of group I avian adenovirus [AA]. Restriction fragment length polymorphism [RFLP] analysis of PCR products using restriction enzyme Hpa II resulted in five bands confirming the presence of AA in the analyzed samples