PATHOGENESIS & EPIDEMIOLOGY
ESSENTIALS OF DIAGNOSIS & TYPICAL FEATURES
Human immunodeficiency virus (HIV) causes progressive destruction of CD4 T lymphocytes, ultimately leading to acquired immunodeficiency syndrome (AIDS).
Perinatal transmission of HIV is declining worldwide due to antiretroviral treatment (ART) and other interventions.
In the United States, adolescents and young adults are at ongoing risk of HIV acquisition, particularly young men of color who have sex with other men.
Pathogenesis & Transmission
Human immunodeficiency virus (HIV) is a retrovirus that can be found in blood, semen, preseminal fluids, rectal fluids, vaginal fluids, and breast milk of persons living with HIV, with transmission occurring via sexual contact, sharing contaminated needles, and several perinatal routes (in utero, peripartum, breast-feeding). Infection resulting from accidental needle sticks or, rarely, mucosal exposure to blood may occur, mainly in health care settings.
At the time of initial infection, HIV migrates to regional lymph nodes, replicates, and spreads to lymphoid tissues throughout the body. Based on nonhuman primate models, replicating virus disseminates by 48 hours postinfection. Approximately 2 weeks after exposure, a high level of virus is detected in the bloodstream (Figure 41–1). In adults without therapy, the level of viremia declines concurrent with the appearance of an HIV-specific host immune response, and plasma viremia usually reaches a steady-state level about 6 months after primary infection. An asymptomatic period usually follows, lasting from 1 year to more than 12 years. However, ongoing viremia and immune activation causes injury to the immune system and other organs.
Typical course of HIV infection. Soon after acute infection, there is a rapid rise in viral load and decline in the number of CD4 T lymphocytes in peripheral blood. As an immune response to HIV develops, the viral load decreases and there is a period of clinical latency. The CD4 T-lymphocyte count continues to decline until the person living with HIV becomes at risk of opportunistic disease and acquired immunodeficiency syndrome. (Reproduced with permission from Wikimedia Commons/Sigve https://commons.wikimedia.org/w/index.php?curid=15383502.)
Infants with peripartum and in utero HIV infection have viremia that rises steeply after birth, reaching a peak at 1–2 months of age. In contrast with adults, infants have a gradual decline in plasma viremia that extends to age 4–5 years. Without treatment, up to 50% of infants will have rapid disease progression to AIDS or death by age 2 years.
HIV integrates its nucleic acid into the DNA of cells of the immune system, including helper T lymphocytes (CD4 T lymphocytes), monocytes, and macrophages. HIV infection, in the absence of treatment, causes progressive immune incompetence with a hallmark loss of CD4 T-lymphocyte numbers, ultimately leading to conditions that meet the definition of AIDS and, eventually, death. AIDS is diagnosed when an individual living with HIV develops any of the stage 3 ...