Characterization of avian adenovirus type-4 causing hydro-pericardium syndrome in broilers in Karachi, Pakistan

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 1 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.