Abstracts Category : Other

First detection of a phylogenetically distinct and highlyprevalent human polyomavirus 6 in human bile samples

by Tee Kah ;

Oncovirus associated malignancies are potentiallypreventable diseases with major public health significance. Humanpolyomaviruses (HPyVs) may be associated with oncogenesis orsymptomatic illnesses in immunocompromised patients, but the siteof viral shedding of most recently discovered HPyVs remainsobscured. Bile samples were collected from patients with malignantbiliary obstruction caused by cholangiocarcinoma, hepatocellularcarcinoma (HCC), pancreatic carcinoma, or gallbladder carcinoma.Bile samples were also collected from patients with acute gallstonecholangitis as controls. A consensus polymerase chain reaction(PCR) assay targeting the large tumor antigen (LTAg) gene of 11known HPyVs was designed and utilized to screen for HPyVs in 124bile samples. Two of 124 (1.6%) bile samples were positive forHPyV6 deoxyribonucleic acid (DNA) in the screening. Subsequently, atotal of 171 bile samples were screened with a specificconventional PCR assay targeting the viral capsid protein (VP1)gene of HPyV6, which detected HPyV6 DNA in 11/171 (6.4%) samples.To better understand the prevalence and the viral loads of HPyV6 inthe bile samples, a more sensitive real-time PCR assay usingspecific primers targeting the HPyV6 LTAg gene was performed. Theoverall prevalence of HPyV6 was higher in the bile samples ofpatients with malignant biliary obstruction (18.8%) than those withacute gallstone cholangitis (5.5%). The prevalence and mean viralload of HPyV6 were the highest in the cholangiocarcinoma subgroup(27.6% and 2.41104 copies/ml). These findings were confirmed withanother real-time PCR assay using specific primers targeting theHPyV6 VP2 gene. Complete genome of 2 representative bile HPyV6strains were sequenced, including one from a patient withcholangiocarcinoma (Bile-81) and another from a patient with acutegallstone cholangitis (Bile-72). These bile HPyV6 strains arephylogenetically distinct from other known HPyV6 strains and mayrepresent a novel clade of HPyV6. They formed a distinct clusterfrom the other HPyV6s and exhibited >2% differences in aminoacid sequences in their major proteins, including small T antigen(STAg) (1.1% to 2.2%), LTAg (1.1% to 2.3%), VP2 (1.2% to 2.1%), andVP3 (1.9% to 2.8%). Comparison of patients with and without HPyV6in bile samples showed that the virus was unlikely the cause of thepatients acute symptoms and liver dysfunction. HPyV6 may beassociated with the pathogenesis of cholangiocarcinoma in patientswithout coinfection with other well established oncogenic pathogensin our locality, such as Clonorchis sinensis, Hepatitis B virus(HBV), and Hepatitis C virus (HCV). Further studies utilizing insitu hybridization for detection of HPyV6 in cholangiocarcinomatissues should be conducted to further investigate on the possibleassociation between HPyV6 and cholangiocarcinoma. published_or_final_version Microbiology Master Master of Philosophy