Extrahepatic biliary atresia can be defined as a progressive necroinflammatory process involving a segment or the entire extrahepatic biliary tree leading to loss of patency of the lumen and obstruction to bile flow . EHBA occurs in 8 in 15000 live births resulting in 250 to 400 new cases per year in the USA . Although we don't have a documented incidence rate of the disease in Iran, we encounter these cases frequently, especially in summer and winter. The pathogenesis of EHBA remains a mystery, though most of the causal theories and research to date can be grouped into four main categories: infectious or toxin exposure, abnormal morphogenesis, genetic predisposition and immune dysregulation . Reovirus and Rotavirus particles have been found in liver and bile duct remnants of patients with EHBA [2, 3]. Evidence for human papilloma virus (HPV) types 6 and 18 has also been reported . There is no evidence for a causative role by hepatitis B or C in the disease . The available data about EBV is rather limited, but there is a serologically documented case on record . However, EBV-associated hepatitis is well recognized .
EBV is a member of the herpesvirus family. As with other herpesviruses, EBV is an enveloped virus that contains a DNA core surrounded by an icosahedral nucleocapsid and infection is endemic around the world . It is now known that EBV infects 90% of the world's adult population. Upon infection, the individual remains a lifelong carrier of the virus . Available detection methods for EBV are: PCR, in situ hybridization (ISH) and immunohistochemistry (IHC). ISH is the standard procedure for detecting EBV-encoded RNAs (EBERs) . According to some authors, PCR and chromogenic in situ hybridization (CISH) are equally sensitive in detecting EBV in routinely processed liver biopsies, while IHC is an insensitive method . Although larger biopsies are generally needed for CISH, in contrast to PCR, it allows identification and distinction of infected cell types . This is generally considered an advantage, since the correct diagnosis of EBV hepatitis requires detection of the EBERs in parenchymal cells, not periportal lymphocytes . The ready implementation of ISH in pathology laboratories makes it a useful ancillary tool in confirming the diagnosis of EBV infection in equivocal cases. This technique is based on detection of EBV-encoded RNAs (EBERs). EBER 1 and 2 are nonpolyadenylated, uncapped, noncoding RNAs of 167 and 172 nucleotides respectively, and are expressed abundantly in nearly all EBV-infected cells . Peptide nucleic acid (PNA) probes are usually employed for hybridization. PNA molecules are DNA mimics, where the negatively charged sugar-phosphate backbone of DNA is replaced by a neutral polyamide backbone formed by repetitive units of N-(2-aminoethyl) glycine . Individual nucleotide bases are attached to each of the units to provide a molecular design that enables PNA to hybridize to complementary nucleic acid targets according to the Watson and Crick base-pairing rules. The synthetic backbone provides PNA probes with unique hybridization characteristics, such as more rapid and stronger binding to complementary targets .
EBV infection is seen in Iran rather commonly and we suggest a role for it at least in a fraction of EHBA cases. There is limited data in EHBA on the role of EBV infection, so we decided to study the presence of EBV virus in a series of 16 proven EHBA cases by CISH technique.