Two types of 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. HIV results in a broad spectrum of disease, with AIDS representing the most severe end of the clinical spectrum.
The Joint United Nations Program on HIV/AIDS estimated that 33.3 million people worldwide were infected with HIV-1 at the end of 2009. More than 95% of the total cases reside in developing countries. In the same year, an estimated 370,000 children contracted HIV during the perinatal and breast-feeding period, down from 500,000 in 2001 (down 24%). This drop reflects the fact that access to services for preventing the mother-to-child transmission (MTCT) of HIV has increased. On the other hand, the estimated number of children living with HIV increased to 2.5 million worldwide in 2009, mainly due to a decrease in AIDS-related mortality as antiretroviral drugs (ARDs) becomes more available. Currently, the Centers for Disease Control and Prevention (CDC) estimates that each year, 215–370 infants with HIV infection are born in the United States; this is a significant drop from 1650 in 1991.
HIV-1 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. This DNA is transported to the nucleus and integrated into the host genome DNA. There is eventual destruction of both the cellular and humoral arms of the immune system. As well, HIV-1 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 jiroveci 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 disease/sexually transmitted infection (STD/STI) during pregnancy. Several mechanisms/predisposing factors for viral transmission exist, including maternal disease state, fetal exposure to infected maternal body fluids, depressed maternal immune response, and breast-feeding. Maternal plasma HIV RNA level is the best single predictor of MTCT risk. Other risk factors include mode of delivery, duration of rupture of membranes (the risk increases with each hour increase in the duration), prematurity and low birthweight, cervical-vaginal viral load, low CD4+ cell count, ...