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.

Three fowl adenovirus (FAV) isolates (341, 344, and 215) obtained during 1996-97 from field outbreaks of inclusion body hepatitis/hydropericardium syndrome (IBH/HPS) affecting broilers and broiler breeders in Chile were characterized by virus neutralization tests (VNTs) and restriction enzyme analysis of a DNA fragment. Furthermore, the pathologic characteristics of one of these FAV isolates (FAV 341) was studied in experimentally infected chickens. The VNTs conducted with isolates 341 and 344 against reference strains and antisera belonging to each of 12 FAV serotypes demonstrated a close antigenic relationship with strain KR5 of the FAV serotype 4. Polymerase chain reaction using the primers H3/H4 and subsequent HpaII digestion was used for serotype identification of isolates 341 and 215. The length of the PCR products and the restriction profiles of isolates 341, 215, and the reference strain KR5 (FAV4) were identical. The present results confirmed the classification of all three isolates as FAV4. The pathogenicity test with 1000 mean tissue infectious dose of isolate 341 inoculated intramuscularly in 20-day-old specific-pathogen-free chickens resulted in the death of 9% (two birds) six days postinoculation (PI). Both birds showed characteristic IBH/HPS gross and microscopic lesions; the remaining birds, sacrificed at day 10 PI, showed less severe lesions. On the basis of epidemiologic and experimental data of the virulence of Chilean FAV isolates, and the pathogenicity results with isolate 341, we speculate that Chilean FAV strains may require an association with other agents (immunosuppressive agents) to induce IBH/HPS outbreaks in the field.

Serology, restriction enzyme analysis and polymerase chain reactions were used to classify a total of 12 fowl adenoviruses (FAV) isolated from clinical cases of infectious hydropericardium from ® eld outbreaks in seven countries in Asia and America. All isolates belonged to FAV serotype 4. Two isolates were contaminated with avian adeno-associated virus and one of them also contained FAV1. Minor differences were observed in the BamHI restriction pro® les. More variability was seen with SmaI, BglII and PstI restriction pro® les. However, more than 80% of the fragments were identical in size in the ® ve different PstI pro® les, indicating the close genomic relationship between the isolates. Polymerase chain reaction assays supported the classi® cation of the isolates as FAV4 strains. All isolates could be detected using H1/H2 or H3/H4 primer pairs. Restriction enzyme analysis of the H1/H2 polymerase chain reaction (PCR) products allowed no differentiation between the isolates, whereas the three isolates from India and Pakistan could be separated from all others after HpaII digestion of the H3/H4 PCR products. Although strain variation was demonstrated, it could be shown that all adenoviruses isolated from various ® eld cases of infectious hydropericardium (Angara Disease) in several countries belong to fowl adenovirus serotype 4.

Virus shedding by vaccinated birds was markedly reduced.

The susceptibility of chicken embryo liver (CEL) and chicken kidney (CK) cells to eight adenoviruses isolated from different pigeons were investigated. Isolation and propagation was most successful in CEL cells. The cytopathic effect, i.e. cell rounding and detachment of the cells was typical for adenoviruses. Titres of up to 10(6.6) plaque-forming units/ml could be reached on CEL cells. Transferring CEL-grown virus onto CK cells also resulted in a cytopathic effect but with much lower titres, whereas the isolation of pigeon adenoviruses on these cells was not successful. Antibodies against fowl adenovirus reference strains (FAV1-12) were used to serotype the isolates in neutralisation tests. Six were identified as FAV serotypes 2,5,6,10 and 12. Two isolates could not be typed. An antiserum produced in chickens against one of these untypable strains was able to neutralize both. The neutralization indexes of these strains were very similar, indicating that they are probably the same serotype. A cross neutralization test confirmed that this serotype is different from known fowl adenoviruses.