Transfusion-transmitted diseases: risks, prevention and perspectives

During the past decades major improvements in blood safety have been achieved, both in developed and developing countries. The introduction of donor counseling and screening for different pathogens has made blood a very safe product, especially in developed countries. However, even in these countries, there is still a residual risk for the transmission of several pathogens. For viruses such as the human immunodeficiency virus (HIV), and the hepatitis viruses B and C, this is due mainly to window-period donations. Furthermore, the threat of newly emerging pathogens which can affect blood safety is always present. For example, the implications of the agent causing new variant Creutzfeld-Jakob disease for transfusion practice are not yet clear. Finally, there are several pathogens, e.g. CMV and parvo B19, which are common in the general donor population, and might pose a serious threat in selected groups of immunosuppressed patients. In the future, further improvements in blood safety are expected from the introduction of polymerase chain reaction for testing and from the implementation of photochemical decontamination for cellular blood products. The situation in transfusion medicine in the developing world is much less favorable, due mainly to a higher incidence and prevalence of infectious diseases.

A matter for debate: the risk of bovine spongiform encephalopathy to humans posed by blood transfusion in the UK

If human infection with bovine spongiform encephalopathy (BSE) were to occur, donated peripheral blood from humans that might have become infected from eating adequate quantities of food containing BSE should, until evidence is available to the contrary, be assumed to contain the human form of the disease. The chance of disease transfer to a blood recipient in 1995, which might in turn cause clinical disease with an incubation period of 20 years, is calculated. Transfusion is calculated to be a potential cause of a maximum of only 0.2% of clinical cases of Creutzfeldt-Jakob disease (CJD) in the UK population if the BSE epidemic were to spread to humans. Prospective epidemiological techniques would be unlikely to demonstrate any such minor contribution that blood transfusion might make to CJD incidence.

Transfusion-transmitted disease

Many patients with haemophilia are infected with viruses, due to treatment with blood products--particularly from large pool clotting factor concentrates before 1985. AIDS in haemophilic patients was first described in 1982 and it has significantly reduced the life expectancy of these patients. Although no new sero-conversions have occurred since 1986, management of HIV in haemophilia remains a clinical challenge. Transfusion-associated hepatitis was recognized in 1943, and it is now an important complication of haemophilia treatment. Vaccination against HAV is recommended. Intensively-treated older haemophilic patients usually have serological evidence of HBV infection. HBV transmission has been stopped, but hepatitis B vaccination is still practised, because HDV requires HBV for propagation. Many patients are infected with HCV: before 1985 almost all patients who received clotting factor concentrate developed non-A, non-B hepatitis, now recognized as HCV. Treatment strategies are being developed for HCV in haemophilic patients. Parvo virus can be transmitted by clotting factor concentrate; it is very resistant to sterilization processes, transmission causing severe illness even in immuno-competent individuals. New blood-borne viruses responsible for sero-negative hepatitis include: GBV-A, B and C, and HGV. Although there is no link between CJD and haemophilia, there is concern about possible blood product transmission.