Molecular and Histopathological Study on Circulating Fowl Adenovirus Serotypes Causing Inclusion Body Hepatitis (Ibh) in Broiler Chickens in Sri Lanka

Inclusion Body Hepatitis (IBH) is an emerging acute viral disease in Sri Lanka caused by Fowl Adenoviruses (FAdVs) of the genus Aviadenovirus, family Adenoviridae. It primarily affects broilers aged 3–7 weeks, leading to liver damage and significant economic losses. Histopathological diagnosis of IBH is based on the presence of pathognomonic intranuclear basophilic inclusion bodies in degenerating hepatocytes. Molecular diagnosis of IBH involves the detection of the hexon gene of the FAdV using conventional PCR. The serotyping, based on the hexon gene L1 loop variable region, is important for developing effective vaccination strategies. This study aimed to identify circulating FAdV serotypes responsible for IBH in broilers in the Western, North Western, and Central provinces of Sri Lanka. A total of 76 dead broilers were collected/ received; Western (n = 23), North Western (n = 38), and Central (n = 15). Clinical history, vaccination data, and performance records were documented. The liver was the primary organ examined. Gross and histopathological evaluations were performed, and histopathological confirmation of IBH was based on intranuclear basophilic inclusion body detection. The gross lesions observed in all the examined livers had hepatomegaly, petechial haemorrhages and multifocalcoalescing necrotic patches. PCR was conducted on histopathologically confirmed IBH-positive samples (n = 28/76), of which 19 were PCR-positive (n = 19/28). Three PCR-positive samples from each province were selected for hexon gene sequencing using the Sanger method. Sequencing revealed serotype FAdV-8b in both the North Western and Central provinces and FAdV-11 only in the North Western province. No sequence data could be obtained from the Western province. These findings highlight the presence of different FAdV serotypes contributing to IBH in Sri Lanka and emphasise the need for region-specific surveillance and vaccination strategies.