Some strains of serotype 4 fowl adenoviruses cause inclusion body hepatitis and hydropericardium syndrome in chickens.

Fowl adenoviruses were isolated and characterized from severe cases of hydropericardium syndrome in Ecuador and Pakistan. All were neutralized by antibodies against serotypes 4 and 11. Cross-neutralization tests and restriction enzyme analysis strengthen the classification as serotype 4 strains. The restriction endonucleases used allowed the differentiation among field isolates and reference strains. All field isolates tested induced high embryo mortality. One-day-old specific pathogen free (SPF) chicks were infected with 10(5) plaque-forming units by natural routes to reproduce the disease with plaque purified virus. Whereas no mortality was seen with the reference strain, the mortality with the field isolates was 100%. A reduced mortality occurred with a lower infectious dose. Field isolate K1013 from Ecuador was also highly pathogenic for 1- to 3-week-old SPF chicks after intramuscular inoculation. The main pathological signs were swollen livers, severe hydropericardium and nephritis, reflecting the field situation and underlining the role of FAV4 strains in the aetiology of infectious hydropericardium.