Hepatitis viruses

Donors with a history of hepatitis are deferred for 12 months.

When serum from an individual with hepatitis B virus is ultra-centrifuged and examined with the electron microscope, three types of particle may be seen. The large (42-nm diameter) Dane particle is the actual virus with its central nucleocapsid core, which has its own antigenic constituent HBc. The core contains partially double-stranded DNA and DNA polymerase, and is surrounded by a lipoprotein coat carrying the surface antigen (HBsAg). The other two types of particles are 20-nm rods and spheres and represent overproduction of surface antigen material. The HBe antigen is in soluble form and is present in the incubation period, during acute infection and during the first years of the carrier phase. HBeAg is a marker of high infectivity. Dane particles are very rare in the plasma of low-infectivity carriers.

All donations are tested for the presence of hepatitis B surface antigen (HBsAg) by sensitive enzyme-linked immunosorbent assays (ELISAs) that can detect at least 0.2 IU/mL of HBsAg.

Hepatitis C virus (HCV) is recognized as the cause of the majority of cases of what was previously known as non-A non-B (NANB) hepatitis. Although electron microscopic visualization of HCV has not been verified, its genome has been cloned and ELISAs have been developed in which cloned and/or synthetic peptides can react with antibody to HCV.

Individuals with a history of jaundice may be accepted as donors, provided that they have been shown to be negative for markers of HBV and HCV. Clinical jaundice may be due to causes other than hepatitis B and C, including non-viral causes; also the majority of donors who are positive for HBsAg have no such history, so there is no sense in rejecting all people who give

Table 16.4 Transfusion-transmissible agents.

Agents

Characteristics related to transfusion

Viruses Hepatotropic

Retroviruses

Herpesviruses

Others

Bacteria Endogenous

Exogenous

Parasites

Prions

HAV HBV HCV

HIV1 and HIV2 HTLV-I and HTLV-II

CMV EBV

Parvovirus B19

West Nile virus

Treponema pallidum Yersinia enterocolitica

For example, Staphylococcus epidermidis; micrococcus, sarcina

Malaria

Chagas' disease Abnormal PrP

Very rarely transfusion transmitted; no carrier state; faecal-oral transmission 2- to 6-month incubation period; carrier state; readily transmissible by blood Majority of cases asymptomatic; carrier state; readily transmissible by blood

Carrier state and latent in WBCs; readily transmissible by blood Latent in WBCs

50% UK adults have been infected; latent in WBCs

Most UK adults have been infected (therefore already exposed pretransfusion); latent in WBCs

Generally mild or asymptomatic, posing no transfusion risk except for non-immune aplastic anaemia patients and fetuses Approximately two-thirds of UK adults have been infected Seasonal variation (and epidemic years) in incidence rate

Recently exhibiting epidemic rates of transmission in summer months in North America

Inactivated by storage at 4°C

No transfusion transmissions reported in the past 15 years

Very occasional transmissions, usually contaminated red cells transfused late in the storage period

Mainly skin commensals or contaminants Most common cause of platelet contamination

Only five verified transfusion cases reported in UK in 25 years (all Plasmodium falciparum)

No transmission of Trypanosoma cruzi by transfusion has been reported in UK Possible transfusion risk from vCJD; two UK cases potentially transfusion transmitted a history of clinical jaundice. In the UK, the incidence of HBsAg in first-time blood donors is approximately 1 in 2000 and in established donors (i.e. new infections) less than 1 in 100 000. Hepatitis B surface antigen-positive subjects are permanently excluded from donation, and should be under specialist follow-up, as they have an increased risk of developing chronic liver disease and hepatocellular carcinoma.

Although the transmission of hepatitis B by blood and blood components has been virtually eliminated, HBsAg testing will not exclude all donors capable of transmitting HBV, as the sensitivity of presently available techniques may allow as many as 104-106 HBV genome copies per millilitre of plasma to remain undetected. The introduction of screening for anti-HBc and/or HBV DNA would reduce the very low risk of transmission of HBV yet further, but is not justified in the UK because of the striking rarity of reports of post-transfusion hepatitis B in recent years.

In the USA, before screening for anti-HCV was introduced, about 10% of transfusions caused significant increases in transaminase activity in recipients. There were also occasional cases of symptomatic hepatitis. Acute HCV infection is usually mild, but a proportion of patients do develop chronic liver disease, with a risk of hepatocellular carcinoma. Confirmed rates of HCV positivity in the UK are 1 in 2000 for new donors and < 1 in 100 000 for repeat donors. Methods of heat inactivation and solvent-detergent treatment of factors VIII and IX prevent transmission of HCV. Haemophiliacs who have received effectively inactivated factor VIII have proved negative for anti-HCV, in contrast with those who received untreated concentrate.

Hepatitis A virus is rarely transmitted by transfusion. Any donor who has been in close contact with a case (e.g. household contact), or developed hepatitis A is deferred for 12 months.

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