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7r <br />Infectious Agents Transmitted by Blood <br />Of the many infectious agents present in.the blood bank, <br />viruses are most numerous, and of the viral agents, those <br />that transmit hepatitis are the most common. Several <br />different viruses cause hepatitis or inflammation of the <br />liver; three will be discussed here: hepatitis A virus <br />(HAV), hepatitis B virus (HBV), and hepatitis C virus (HCV). <br />Hepatitis A <br />Hepatitis A is caused by a 27 -nanometer ribonucleic acid <br />(RNA) virus. Transmission of this picornavirus occurs <br />primarily by the fecal -oral route and is frequent when <br />sanitation is poor and there is close contact between <br />infected persons. Common source exposures from contaminated <br />food and water also occur. Individuals exposed to HAV <br />commonly have a complete recovery and develop immunity to <br />the virus. The infection is rarely trans-mitted by blood <br />products, although isolated cases have been reported. <br />Therefore, transmission of hepatitis A infection in the <br />blood bank setting is rare and should be prevented by <br />frequent hand washing. <br />Hepatitis B <br />Hepatitis B infection is caused by a 42 -nanometer deoxyribo- <br />nucleic acid (DNA) virus belonging to the class known as <br />Hepadna viruses. Despite the fact that the virus has not <br />been grown in tissue culture, much is known about its struc- <br />ture and epidemiology. <br />Intact HBV is found in the serum of acutely and <br />chronically infected persons. The surface of the 42 -nano- <br />meter virus is composed of HBsAg, a 22 -nanometer sphere or <br />tubule. Large quantities of this surface protein are re- <br />leased into the serum during HBV infection. HBsAg usually <br />appears from 1 - 2 months before the onset of symptoms, and <br />40 - 180 days after exposure. <br />Several subtypes of HBsAg exist, and these are of epi- <br />demiological interest. All HBsAg subtypes contain the "a" <br />determinant and either the "d" or "Y" and the "w" or "r" de- <br />terminant. In the US and Western Europe, "adw" is the most <br />common subtype among chronic carriers, hence among blood <br />donors. <br />BIOSAFETY - INFAGT - 0491 - PAGE 1 <br />