HIV Infection and AIDS: Background, Pathophysiology, Etiology
Human immunodeficiency virus (HIV) is a blood-borne virus typically transmitted via sexual intercourse, shared intravenous drug paraphernalia, and mother-to-child transmission (MTCT), which can occur during the birth process or during breastfeeding. HIV disease is caused by infection with HIV-1 or HIV-2, which are retroviruses in the Retrovir...
This site is intended for healthcare professionals News & Perspective Tools & Reference CME/CE More EN Register Log In X AI Mode Tools & Reference>Infectious Diseases HIV Infection and AIDS Updated: Jan 03, 2025 Author: Shelley A Gilroy, MD, FACP, FIDSA; Chief Editor: Michael Stuart Bronze, MD more... Background Human immunodeficiency virus (HIV) is a blood-borne, sexually transmissible virus (see the image below.) The virus typically is transmitted via sexual intercourse, shared intravenous drug paraphernalia, and perinatally during the birth process or via human milk. View Media Gallery The most common route of infection varies from country to country and even among cities, reflecting the population in which HIV was introduced initially and local practices. Co-infection with other viruses that share similar routes of transmission, such as hepatitis B, hepatitis C, and human herpes virus 8 (HHV8; also known as Kaposi sarcoma herpes virus [KSHV]), is common. Two distinct species of HIV (HIV-1 and HIV-2) have been identified, and each is composed of multiple subtypes, or clades. All clades of HIV-1 tend to cause similar disease, but the global distribution of the clades differs. This may have implications on any future vaccine, as the B clade, which is predominant in the developed world (where the large pharmaceutical companies are located), rarely is found in the developing countries that are more severely affected by the disease. HIV-1 probably originated from one or more cross-species transfers from chimpanzees in central Africa. [1] HIV-2 is closely related to viruses that infect sooty mangabeys in western Africa. [2] Genetically, HIV-1 and HIV-2 are superficially similar, but each contains unique genes and its own distinct replication process. HIV-2 carries a slightly lower risk for transmission, and HIV-2 infection tends to progress more slowly to acquired immune deficiency syndrome (AIDS). This may be due to a less-aggressive infection rather than a specific property of the virus itself. Persons infected with HIV-2 tend to have a lower viral load than people with HIV-1, [3, 4] and a greater viral load is associated with more rapid progression to AIDS in HIV-1 infections. [5, 6] HIV-2 is rare in the developed world. Consequently, most of the research and vaccine and drug development has been (perhaps unfairly) focused on HIV-1. For information on HIV infection in children, see Pediatric HIV. Initial description and early spread In the United States, HIV disease was first described in 1981 among two groups, one in San Francisco and the other in New York City. Numerous young homosexual men presented with opportunistic infections that, at the time, were typically associated with severe immune deficiency: Pneumocystis pneumonia (PCP) and aggressive Kaposi sarcoma. [7] HIV itself was not identified for another 2 years. [8] During that time, various other causes were considered, including lifestyle factors, chronic drug abuse, and other infectious agents. [9] The HIV epidemic spread rapidly and silently in the absence of testing. However, clear clinical implications arose before society became aware of the disease; for example, prior to the recognition of HIV, only one case of Pneumocystis pneumonia not clearly associated with immune suppression was diagnosed in the United States between January 1976 and June 1980. In 1981 alone, 42 similar diagnoses were made, and by December 1994, 127,626 cases of Pneumocystis pneumonia with HIV infection as the only identified cause of immune suppression had been reported to the Centers for Disease Control and Prevention (CDC). Also, Kaposi sarcoma is up to 30,000 times more likely to develop in persons with HIV infection than in immunocompetent persons. The spread of HIV was retrospectively shown to follow the trucking routes across Africa from logging camps, and the bush-meat trade combined with aggressive logging and improved transportation in the mid-20th century may have allowed what was likely occasional cross-species transmission events to propagate across the country and, eventually, the globe. [10] Stigma of HIV infection A considerable amount of stigma has been attached to HIV infection, mostly because of the virus's association with sexual acquisition and the inference of sexual promiscuity. Consequences of this stigma have included discrimination and reluctance to be tested for HIV infection. The stigma of HIV infection also is associated with a fear of acquiring a rapidly fatal infection from relatively casual contact. Such attitudes are inappropriate because HIV is poorly transmissible without sexual contact or blood contact. In addition, the expected survival is long in patients with HIV infection who are receiving treatment. HIV is not transmitted during casual contact and is readily inactivated by simple detergents. Much of the concern regarding HIV infection is due to the incurability of the infection and the relentless immune decline and eventual premat...