Retrospective Study of Inclusion Body Hepatitis Diagnostic Cases in Chickens in California; 2015-2024

From 2015 to 2024, inclusion body hepatitis (IBH) was diagnosed in a total of 346 chicken necropsy cases submitted to the California Animal Health and Food Safety (CAHFS) laboratory system. The majority of cases (68%; 237/346) originated from a single commercial broiler company with a high density of poultry premises within the California Central Valley region. Reported mortality varied between 0.5% and 4.8% per day, and morbidity ranged between 5% and 10%. Clinical signs observed in affected flocks included depression, reluctance to move, ruffled feathers, greenish diarrhea, and, occasionally, icterus of skin and adipose tissue. Typical histopathological lesions included extensive hepatic necrosis, multifocal pancreatic necrosis, gizzard erosions, and glomerulonephropathy. Intranuclear inclusions were identified, mainly within degenerating hepatocytes, followed by pancreatic acinar cells, glandular epithelium of proventriculus and gizzard, and enterocytes of the small intestines and renal endothelium. Diagnosis was based on microscopic changes characteristic of IBH and a positive conventional PCR targeting the hexon gene of fowl adenovirus (FAdV) on liver tissue pools. Sequence analysis was performed on 41 selected FAdV-positive samples from diagnostic cases. The majority of FAdV PCR-positive samples aligned with FAdV-8b (16/41). However, FAdV-7 (14/41), FAdV-4 (7/41), and FAdV-11 (4/41) were also detected from IBH cases. Disease management was successfully achieved by the administration of an autogenous vaccine to breeders, at 11 and 18 wk of age, to confer maternal antibody protection to the broiler progeny.