Hepatitis B virus (HBV) infection commonly occurs through horizontal transmission via household/close contact. Although the body fluids of patients infected with HBV are likely to play a significant role in horizontal transmission, the precise mechanism remains unclear. In the 1970s, the infectivity of body fluids including saliva, urine, and faeces was assessed for the presence of hepatitis B surface antigen (HBsAg). Over the last decade, the HBV DNA in the body fluids of chronically infected patients was quantified using real-time polymerase chain reaction. Chimpanzee, gibbon, and chimeric mice with human livers have also been used to investigate the infectivity of body fluids. HBsAg levels, HBV DNA levels, and animal experiments have indicated that saliva and tears are able to transmit HBV. Urine and faeces do not lead to horizontal transmission. The infectivity of the remaining body fluids remains controversial. Horizontal transmission is related to both virus and host factors; thus, evaluations of HBsAg and HBV DNA levels provide insufficient data to determine the infectivity of body fluids. Universal hepatitis B vaccination has been implemented worldwide (with the exception of Northern Europe); an understanding of the role that body fluids play in horizontal transmission will contribute to the eradication of HBV.
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