Two types of human immunodeficiency virus (HIV) cause disease in humans: HIV-1 and HIV-2. These are enveloped RNA cytopathic lentiviruses belonging to the family Retroviridae. Infection is most commonly secondary to HIV-1. HIV-2 is rare in the United States but more common in West Africa. Unless otherwise specified, this chapter addresses HIV-1 infection. HIV results in a broad spectrum of disease, with acquired immunodeficiency syndrome (AIDS) representing the most severe end of the clinical spectrum.
The Joint United Nations Program on HIV/AIDS estimated that 36.7 million people worldwide were infected with HIV at the end of 2015. More than 95% of the total cases reside in developing countries. In the same year, an estimated 150,000 children contracted HIV, down from 290,000 in 2010 (down 50%). This drop reflects the fact that access to services for preventing the mother-to-child transmission (MTCT) of HIV has significantly increased. The estimated number of children living with HIV declined to 1.8 million worldwide in 2015. Among infants born in the United States, the overall annual rate of perinatally acquired HIV infections decreased from 3.6 per 100,000 live births in 2008 to 1.8 per 100,000 live births in 2013.
HIV is particularly tropic for CD4+ T cells and cells of monocyte or macrophage lineage. After infection of the cell, viral RNA is uncoated and a double-stranded DNA transcript is made (through the activity of a viral enzyme, reverse transcriptase). This DNA then moves to the nucleus and integrates into the host genome DNA where it persists as a provirus. There is eventual destruction of both the cellular and humoral arms of the immune system. In addition, HIV gene products or cytokines elaborated by infected cells may affect macrophage, B-lymphocyte, and T-lymphocyte function. Hypergammaglobulinemia, caused by HIV-induced polyclonal B-cell activation, is often detected in early infancy. Disruption of B-cell function results in poor secondary antibody synthesis and response to vaccination. A small proportion (<10%) of patients will develop panhypogammaglobulinemia. Additionally, profound defects in cell-mediated immunity occur, allowing a predisposition to opportunistic infections such as fungus, Pneumocystis jirovecii pneumonia (PCP), and chronic diarrhea. The virus can also invade the central nervous system and produce psychosis and brain atrophy.
High-risk mother. Any infant born to a high-risk mother is at risk. High-risk mothers include intravenous (IV) drug users, hemophiliacs, spouses of hemophiliacs, spouses of bisexual males, those with a history of exchanging sex for money or drugs, sex partners of HIV-infected persons, and those who were diagnosed with sexually transmitted infection during pregnancy. Several mechanisms account for viral transmission, but maternal plasma HIV RNA level (viral load) is the best single predictor of MTCT risk. Other risk factors include mode of delivery, duration of rupture of membranes, prematurity and low birthweight, cervical-vaginal viral load, low maternal CD4+ cell count, maternal symptomatic HIV disease/AIDS, viral subtype, and host genetic factors. Most MTCT occurs intrapartum, with smaller proportions of transmission occurring in ...