Abstract
Hydropericardium-hepatitis syndrome (HHS), a recently emerged disease of chickens, is caused by some strains of fowl adenovirus serotype 4 (FAdV-4). In this study, a Canadian FAdV-4 isolate, designated as FAdV-4 ON1, was evaluated for pathogenicity after oral and intramuscular (im) infection of specific pathogen free (SPF) chickens. Pathogenicity was evaluated by observation of clinical signs and gross and histological lesions. The highest viral DNA copy numbers, irrespective of the inoculation route, were detected in the cecal tonsils. Virus titers in cloacal swabs collected over the entire study period were compared between the orally and im inoculated chickens, and the difference in titers between the two groups was significant (P<0.001), the oral group had a higher rank. The antibody response of infected chickens tested by an adenovirus-specific ELISA showed a statistically significant (P<0.001) difference between the orally and im inoculated chickens. The im inoculated chickens had higher values than birds inoculated orally (P<0.001). Serum samples from both groups collected at 14 days post-infection completely neutralized FAdV-4 ON1. In addition, the effects of FAdV-4 ON1 infection on transcription of a number of avian cytokines were studied in vivo. The expression of interferon (IFN)-γ and interleukin (IL)-10 in the liver was induced at early times after infection. This FAdV-4 ON1 potentially could be used as a live vaccine against HHS and developed as vaccine vector. The GenBank/EMBL/DDBJ accession number for the FAdV-4 ON1 sequence is GU188428.
Highlights
Fowl adenovirus serotype 4 (FAdV-4) plays a major role in the aetiology of a very important disease in broiler chickens called hydropericardium-hepatitis syndrome (HHS)
Gross pathology and histology Clinical signs indicative of HHS and characterized by depression, chickens huddling in corners with ruffled feathers, and chickens exhibiting the characteristic posture, with the chest and beak resting on the ground, were not seen in any chicks
There were no clinical signs, or gross and histopathological lesions in any of the inoculated birds by either inoculation route, even though they were inoculated with a high virus dose, suggesting it could be considered non-pathogenic
Summary
Fowl adenovirus serotype 4 (FAdV-4) plays a major role in the aetiology of a very important disease in broiler chickens called hydropericardium-hepatitis syndrome (HHS). It was first seen in Pakistan in 1987 [23] and since outbreaks have been reported in India, the Middle East, Japan, Mexico, Peru, Ecuador, and Chile [3,10,20,40] causing significant losses to the poultry industry. Inactivated liver homogenates from infected chickens, and inactivated virus propagated in cell culture and/or embryonated eggs based vaccines are available, they provide only variable protection [6,25]. Schonewille et al (2010) reported live FAdV-4 vaccine, but with lack of neutralizing antibodies
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