Diagnosis of Inclusion Body Hepatitis in Chickens by Impression Smear Cytopathology

Numerous reports and epidemiologic investigations in recent years identify adenoviral infection as an ongoing to increasing, international disease in commercially raised chickens. Impression smear cytopathology was evaluated as a tool for the diagnosis of adenoviral inclusion body hepatitis (IBH). In this study, 92, paired, Romanowsky-stained cytopathologic preparations and hematoxylin-and-eosin-stained histopathologic liver sections were evaluated from 54 chickens with experimentally induced or naturally occurring IBH. Large intranuclear inclusion bodies typical of adenoviruses were visible within hepatocytes on both cytopathology and histopathology. Cytopathologic to histopathologic percent positive agreement and percent negative agreement were 94% and 90%, respectively, with Π= 0.81 (0.61-1.01, 95% confidence, P < 0.001). A subset of 20 cytopathologic samples evaluated by eight veterinary professionals as consistent or inconsistent with IBH yielded an average of 66% positive agreement and 98% negative agreement to the histopathologic diagnosis, across all observers, with Π= 0.61 (0.53-0.68, 95% confidence, P < 0.001), resulting in a positive predictive value of 99% and a negative predictive value of 67%. Interobserver agreement was slightly higher (76% positive agreement, 94% negative agreement, Π= 0.68 [0.65-0.71], 95% confidence, P < 0.001) within the 12 of these samples that originated from natural disease, with stable positive and negative predictive values. A rapid, cost-effective, tentative diagnosis of IBH via impression smear cytopathology at the time of necropsy can streamline further confirmatory laboratory testing and facilitate timely communication in the interim to affected parties, especially in locations with delayed access to a diagnostic laboratory.