AIDS or acquired immunodeficiency syndrome - was originally defined empirically by the Centers for Disease Control and Prevention(CDC) as “the presence of a reliably diagnosed disease that is at least moderately indicative of an underlying defect in cell-mediated immunity.” Following the recognition of the causative virus, HIV, and the development of the sensitive and specific tests for HIV infection, the definition of AIDS has undergone substantial revision. The current surveillance definition categorizes HIV-infected persons on the basis of clinical conditions associated with HIV infection and CD4+T lymphocyte counts. Etiology
AIDS is caused by the infection with the human retroviruses HIV-1 or HIV-2. HIV-1 is the most common cause worldwide; HIV-2 has about 405 sequence homology with HIV-1, is more closely related to simian immunodeficiency viruses, and has been identified predominantly in western Africa. HIV-2 infection has now, however, been reported in europe, south america, canada, and the united states. These viruses are passed through sexual contact; through contact with blood, blood products, or contaminated intravenous needles; intrapartum or perinatally from mother to infant; or via breast milk. Ther e is no evidence that the virus can be passed through casual or family contact or by insect bites such as mosquitoes. There is a definite, though small, occupational risk of infection for health care workers and laboratory personnel who work with HIV-infected specimens. The risk of transmission of HIV from an infected health care worker to his or her patients throug invasive procedures is extremely low. Epidemiology
By january 1, 1997, a cumulative total of approximately 570,000 cases of AIDS has been reported in the United States; approximately 60% of those had died. It has been estimated that there are between 630,000 and 897,000 HIV-infected people in the U.S. Major risk groups continue to be men who have had sex with men and men and women injection drug users; however, the numbers of the cases that are transmitted heterosexually, particularly among women, are increasing rapidly. These women also transmit the infection to their children. As the majority of IDU-associated cases are among inner-city minority populations, the burden of HIV infection and AIDS falss increasingly and disproportionately on minorities, especially in the cities of the Northeast and Southeast U.S. Cases of AIDS are still being found among individuals who have received contaminated blood products in the past, although the risk of acquiring new infection through this route is extremely small in the U.S. HIV infection/AIDS is a global pandemic, especially in developing countries. Pathophysiology and Immunopathogenesis
The hallmark of HIV disease is a profound immunodeficiency resulting from a progressive quantitative and qualitative deficiency of the subset of T lymphocytes referred to as helper or inducer T cells. This subset of T cells is defined phenotypically by the expression on the cell surface of the CD4 molecule, which serves as the primary cellular receptor for HIV. Recently, it has been demonstrated that a coreceptor must be present with CD4 for efficient entry of HIV-1 into target cells. These coreceptors belong to the seven-transmembrane-domain G protein-coupled family of receptors. The molecule termed CXCR4, or fusin, is the coreceptor for T cell-tropic strains of HIV-1, and the B-chemokine receptor CCR-5 is the coreceptor for the macrophage-tropic starins of HIV-1. Although the CD4+T lymphocyteband CD4+ monocyte lineage are the pricipal cellular targets of HIV, virtually any cell that expresses CD4 along with one of the coreceptors can potentially be infected by HIV. Primary infection
Following the initial transmission, the virus infects CD4 + cells, probably T lyphocytes, monocytes, or bone marrow-derived dendritic cells. Both during this initial stage and later in infection, the lymphoid...