Why Is HIV Rarely Transmitted by Oral Secretions?

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Abstract
HUMAN immunodeficiency virus (HIV) transmission from oral secretions of the millions of HIV-viremic individuals during kissing, dental treatment, biting, and aerosolization is a rare event, even when infectious HIV is shed into the oral cavity by infected blood or exudate.1-8 Despite this shedding of infected blood or exudate, saliva of infected individuals usually contains only noninfectious components of HIV, indicating that there may be a breakdown or inactivation of infectious HIV, and may contain fragments or the entire noninfectious genome.9-11 Only 1% to 5% of patients' saliva contains infectious HIV although they all carry virus in their blood.2,12,13 At other mucosal surfaces (vaginal and seminal fluids), the percentage of patients shedding infectious HIV is much higher (approximately 20%).14-16 Also, most of the HIV shed at any mucosal surface during the asymptomatic infection originates from infected mononuclear leukocytes17-25 because most of the cell-free virus in body fluids is neutralized by antibody produced after the initial acute infection.24-27 In addition, cell-free infectious HIV or simian immunodeficiency virus (SIV) has low infectivity for the CD4-negative epithelial cells on all mucosal surfaces.16,28,29 However, at the vaginal mucosal surface, shed-infected mononuclear leukocytes deposited with seminal fluid are infectious14-16; they survive and can attach to and infect the HIV-resistant CD4-negative epithelial cells,16,30-33 or penetrate the epithelial layer, and infect susceptible CD4-positive subepithelial mononuclear leukocytes.34-37

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