TT virus infection: prevalence of elevated viraemia and arguments for the immune control of viral load

Background: The most recent polymerase chain reaction (PCR) detection proto cols for the TT virus (TTV) permit one to identify the presence of viral DN A in the serum of a majority of healthy individuals, in the absence of any particular risk factor. This is in contrast with previous epidemiological s tudies that reported a higher prevalence of TTV infection in populations su ch as haemodialysis patients (HD), haemophiliacs, intravenous drug users or diabetics. Objectives: To show that these discrepant results were due to t he different sensitivity (number of viral copies detected) of the detection protocols used in initial and more recent epidemiological studies. Study d esign and results: We designed a standardised primary PCR assay that detect s only viraemia >5x10(3) to 5x10(4) copies:ml for genotypes 1, 2 and 3, and compared the results of this test with those of a nested PCR assay which i s 100-fold more sensitive. Viraemia > 5 x 10(3) to 5 x 10(4) copies/ml were statistically more frequent in HD patients (54.3%), diabetics (54.7%), and HIV-infected patients with CD4 cells < 200/mm(3) (69%) than in blood donor s (37%) or HIV-infected patients with CD4 cells > 500/mm(3) (33%). Conclusi ons: These data suggest a possible relationship beta een the prevalence of elevated viral loads and the level of immunocompetence of the populations s tudied, and therefore that of an immune control of TTV viraemia. This corro borates previous findings showing that the stimulation of the immune system by an interferon treatment was able to clear TTV viraemia. (C) 2001 Elsevi er Science B.V. All rights reserved.