The present study was performed on 133 chronically HCV infected patients to evaluate the prevalence of potential mixed HCV infection in their plasma, PBMCs, and liver biopsy specimens. In 15% of these patients different HCV genotypes were found in these compartments. Multiple HCV genotypes were detected in 3 (2.3%) of 133 plasma, 9 (6.8%) of 133 PBMC, and 8 (18.2%) of 44 liver biopsy specimens.
Mixed infection is infection of an individual with two or more distinct HCV genotypes. Mixed viral infection is of great clinical importance as it may result in more severe disease, unresponsiveness to antiviral therapy or recurrence after the completion of antiviral therapy course[30
In our study, various HCV genotypes presented in PBMCs were different from those found in plasma or liver biopsy specimens (Table ). It means that PBMCs may present some divergent types, which are not detectable in liver biopsy specimens. It reinforces the previous proposed theories in which PBMCs have been known as an extrahepatic replication site for HCV[17,25,26,31-34
It is suggested that infection with one HCV type doesn’t make a barrier to acquisition of other genotypes, therefore multiple exposures to HCV especially in potential risk groups, might lead to several episodes of re-infection and to the establishment of mixed infection in some patients. It is also well known that super infection with a new HCV strain leads to suppression of one virus under the detection limit of PCR while the other one prevails as under antiviral therapy, the displaced strain may become viremic again and may alter the outcome of therapy[30,35-39
In our study the prevalence of mixed HCV infection was estimated about 2.3% in plasma, 6.8% in PBMC, and 18.2% in liver biopsy specimens of chronically infected patients with HCV. Mixed infection with two HCV genotypes have been detected in 1% of HCV-positive patients, using type-specific primers[40,41
]. Also figures of 1.6% to 31% have been reported in multi-transfused hemophiliacs[42,43
Our study demonstrated that a significant proportion of HCV infected patients have divergent HCV genotypes in their PBMCs and liver biopsy specimens which were not detectable in their plasma.
In the present study we used INNO-LiPA™ HCV II genotyping which is currently the most applied method and has more sensitivity than RFLP. One of the problems of INNO-LiPA™ HCV II is that it may underestimate the actual rate of mixed infection[9,30,44
]. According to this, the true prevalence of mixed infection may be higher than estimated in this study.
The second shortcoming is that only 44 of our patients had indication or gave consent to undergo liver biopsy, however, 18.2% of them had multiple HCV genotypes which is a significant proportion of the total. It indicates that hepatocytes are the main reservoirs for HCV. On the other hand since performance of liver biopsy is not possible for all patients, we suggest the assessment of PBMCs as another HCV reservoir for detection of HCV mixed infection[26,34,45
In conclusion, our study shows that patients with hemophilia and thalassemia are from the most high risk groups in whom mixed infection is relatively common. On the other hand failure to treatment and relapse of infection is also frequent in these groups. So it seems that considering the plasma genotype as the target genotype for scheduling of an anti HCV therapy may be one of the factors that leads to the failure of treatment. HCV genotyping in PBMCs or liver biopsy specimens might be beneficial.