Characterization of fowl adenoviruses from outbreaks of inclusion body hepatitis hydropericardium syndrome in Chile

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.