Polymerase Chain Reaction for Hepatitis Delta Virus RNA Identification and Characterization

Abstract

Hepatitis delta virus (HDV) is a defective virus dependent on hepatitis B virus (HBV) for infection. Superinfection by HDV on a HBV chronic carrier state is generally associated with an exacerbation of the underlying liver disease. Several HDV RNA sequences are now available from different viral strains which show a relatively high conservation of sequences, although some differences are shown in some parts of the viral genome. The delta antigen (HDAg) is the only identified viral protein. The diagnosis of delta hepatitis is generally based on the detection of anti-HD antibodies (total and IgM) in serum and detection of HDAg in the liver; this antigen is detectable in serum only for a short time at the onset of acute infection. The use of molecular hybridization techniques for HDV RNA identification has recently proved to be a powerful tool in the appraisal of HDV infections, mainly in patients with acute hepatitis and in immunocompromised subjects, where the pattern of serological HDV markers may be modified. Among these techniques, the polymerase chain reaction (PCR) appears to be very sensitive in detecting HDV RNA sequences, both in liver and in serum samples. This approach is most useful when only small amounts of serum HDV RNA are present, for example in the later stages of chronic infection, in IFN-treated patients, or in otherwise inadequately preserved sera. PCR is also useful in interpreting doubtful Slot test results which could correspond either to a negative or to a weak positive. In addition, HDV PCR is a means for cloning and sequencing and for analyzing HDV genetic variability. We analyzed, in a relatively short time, the whole genome of HDV from the liver of an infected woodchuk after several passages, then compared selected parts of the HDV genome with two unrelated HDV strains isolated from humans. PCR allowed, in these circumstances, a better appraisal in the implications of HDV genome variability.