Chronologic Analysis of Gross and Histologic Lesions Induced by Field Strains of FAdV-1, FAdV-8b, and FAdV-11 in Six-Week-Old Chickens

Abstract

Inclusion body hepatitis (IBH) is a disease affecting broiler chicken flocks worldwide. Several serotypes of fowl adenovirus (FAdV) have been implicated in disease outbreaks, with and without immunosuppression as a predisposing factor. IBH usually occurs in flocks up to 30 days of age; it is seldom seen in older birds. The objective of this study was to determine whether the pathogenicity for older birds of three FAdV field strains, belonging to serotypes 1, 8b, and 11, in the absence of immunosuppressive factors, was akin to that for younger birds, and to establish an effective and economical disease model for assessing cross-protection between serotypes. To achieve this objective, the gross pathology, histopathology, and dissemination of virus were examined at multiple time points after inoculation of 6-wk-old, specific-pathogen-free chickens via intraperitoneal injection. Both FAdV-8b and FAdV-11 generated lesions typical of those associated with outbreaks of IBH, and they were shown to be primary pathogens. The presence and severity of hepatic lesions were used to define two disease stages: degeneration (1-5 days postinoculation) and convalescence (6-14 days postinoculation). During the degenerative stage, FAdV-8b was detected in the liver, kidney, and gizzard of most birds, whereas FAdV-11 was predominantly detected in the liver, and both viruses persisted in the gizzard into convalescence. The pathogenesis of two IBH-associated FAdV strains in 6-wk-old chickens confirms their high level of virulence and also provides an effective experimental model for investigation of cross-protection between FAdVs. It also demonstrates persistence of the virus in the gizzard long after infection, supporting the notion that it is a site of viral shedding.

Isolation and characterization of fowl aviadenovirus serotype 11 from chickens with inclusion body hepatitis in Morocco

“…Indeed, the presence of INIB in hepatocytes have been shown by inoculation of FAdV to specific pathogen free (SPF) embryonated eggs via the chorioallantoic membrane and was observed at 5–6 dpi and the adenovirus particles were identified in liver samples of embryos by transmission electron microscopy [36]. Furthermore, SPF chickens infected with different strains of FAdV showed the presence of INIB in hepatocytes at the histological examination of liver tissues [32, 37, 38].…”

“…The nucleotide sequences analysis showed that the three FAdV isolates belonged to FAdV serotype 11 of the D genotype group. This strain was responsible for different inclusion body hepatitis outbreaks in poultry in Canada [28], China [59], Hungary [29], Australia [38], Lebanon [31], Spain [32] and Iran [60].…”

Vaccination with FAdV-8a induces protection against inclusion body hepatitis caused by homologous and heterologous strains

“…Based on previous studies (Yates et al, 1977;Mockett & Cook, 1983) a three-week period was considered optimal for the development of protecting antibodies. Other factors taken into consideration included a suitable age and size of birds to safely administer the IM vaccination, as well as an appropriate age to challenge the birds following the three week period for development of immunity, which was identified as 6 weeks of age in a previous study (Steer-Cope et al, 2017).…”

“…Inoculation was performed via intraperitoneal (IP) injection with 0.5 mL of inoculum containing 10 6 TCID 50 of the virus. The dose was deemed to be suitable for inducing a strong challenge response without resulting in sudden mortality, due to the lower susceptibility to infection of older birds observed in a previous study (Steer-Cope et al, 2017). The birds in the fourth group were inoculated with sterile phosphate-buffered saline (PBS) and used as negative controls.…”

“…They were then euthanized by intravenous injection of sodium pentobarbitone (Virbac Australia Pty Ltd.) and necropsied. In a previous study, day four postchallenge was found to be the peak occurrence of lesions and virus detection in birds of this breed and age during the 1-7 day period following challenge (Steer-Cope et al, 2017). Ethics approval for the animal experiment was granted by The University of Melbourne Animal Ethics Committee (approval number 1212411).…”