Viruses and prions: update on blood safety

The blood borne viruses must be separated into major and minor agents. Majo r viruses transmissible by blood transfusion are human immunodeficiency vir us (HIV) and hepatitis B and C viruses (respectively HBV, HCV). The prevale nce of virological markers in French blood donors has been continuously dec reasing since the implementation of serological screening methods as soon a s they were available. In 1998, the prevalences (per 10,000 donations) were 0.17 for antibody to HIV, 0.08 for antibody to human T-cell leukemia virus (HTLV), 2.23 for hepatitis B surface antigen (HBs Ag) and 2.52 for antibod y to HCV. The values are, of course, higher in new donors when compared to regular donors: approximately five-fold for HIV, 50-fold for HCV and 300-fo ld for HBs Ag. The remaining major questions concern the residual risk due to infectious donations which could escape the preventive measures. It seem s evident that the major risk is imputable mainly to donations collected du ring the window period. During the 1996-1998 period, the residual risk for HIV was 1 our of 1,350,000 donations, 0 for HTLV, 1 out of 375,000 for HCV, and 1 out of 220,000 Jor HBV. A few cases of "immunosilent" patients have been reported. They remain exceptional. The first data col lected after the implementation of nucleic acid technology (NAT) confirm the very low resid ual risk. The recent introduction of leukodepletion probably brought an imp ortant contribution to diminishing the risk of transmission of leucotropic viruses such as cytomegalovirus (CMV), Epstein-Barr virus (EBV), human herp esviruses-6, -7 and -8, and HTLV. If the purification process of plasma-derived medicinal products including inactivation procedures makes it possible to be confident with the eliminat ion of infectivity due to enveloped viruses, the detection of nucleic acid sequences derived from naked viruses in plasma pools such as parvovirus B19 or hepatitis A virus (HAV), and/or the introduction of a nanofiltration st ep during the purification process, when possible, may greatly contribute t o their safety. The emergence of a new form of the Creutzfeldt-Jakob disease (nvCJD) introd uces a new series of questions about the safely of blood products that, alt hough the risks appear limited, are not yet resolved. (C) 2000 Editions sci entifiques et medicales Elsevier SAS.