Human immunodeficiency virus (HIV) infection is caused by one of two similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and weaken cellular immunity, increasing the risk of opportunistic infections and cancers. The initial infection may cause an unspecific febrile illness. The risk of subsequent manifestations, associated with immune deficiency, is proportional to the reduction in CD4+ lymphocytes. HIV can directly damage the brain, glands, kidneys and heart, causing cognitive impairment, hypogonadism, renal failure and cardiomyopathy. Manifestations range from asymptomatic transmission to acquired immunodeficiency syndrome (AIDS), which is determined by serious opportunistic infections, cancer, and a decrease in CD4 count < 200/µL. HIV infection can be diagnosed with antibodies, nucleic acids (HIV RNA) or antigen (p24) tests. Screening should be conducted regularly for all adults and adolescents. Treatment aims to suppress the replication of HIV using a combination of ≥ 3 HIV enzyme inhibiting drugs; treatment can restore immune function in most patients if the replication suppression persists.
Retroviruses – encapsulated RNA viruses combined by a common replication mechanism using reverse transcription to produce DNA copies that are integrated into the host cell genome. Some retroviruses, including 2 types of HIV and 2 types of human T-lymph viruses (HTLV-Infections with human T-lymph viruses), cause severe disease in humans.
HIV-1 is the cause of most HIV infections worldwide, and HIV-2 is more prevalent in parts of West Africa. In some parts of West Africa, both viruses are spread and can infect patients at the same time. HIV-2 appears to be less virulent than HIV-1.
HIV-1 appeared in Central Africa in the first half of the 20th century, when the HIV-like virus chimpanzees first infected people. Epidemic global spread began in the late 1970s, and AIDS was recognized as an independent disease in 1981.
The World Health Organization (WHO) estimates that in 2017 about 36.9 million people worldwide, including 1.8 million children (< 15 years), were living with HIV; approximately 25.7 million of the total were living in sub-Saharan Africa. About 25% of people living with HIV were undiagnosed. Among people who knew they were infected, 79% had access to treatment. About 940 000 people died of AIDS-related illness worldwide in 2017 (70% in sub-Saharan Africa), compared to 1.9 million in 2004 and 1.4 million in 2010. In 2017, an estimated 1.8 million people, including 180,000 children, were newly infected with HIV, up from 3.4 million new infections in 1996. The majority of new infections (95%) now occur in developing countries; more than half of those newly infected are women from sub-Saharan Africa. In many sub-Saharan African countries, HIV infection rates are markedly lower than they were a decade earlier; however, important gaps remain waiting for action from the World Health Organization to end the AIDS epidemic by 2030.
In the United States, an estimated 1.1 million people ≥ 13 years of age are living with HIV in 2015; about 15% of them are diagnosed with HIV. Overall, the number of new cases fell by 19% between 2005 and 2014. In 2016, 39,782 cases were diagnosed. More than two-thirds (67% or 26,570) of new infections occur through homosexual contact between men. Among gay and bisexual men, the number of new infections was 10,223 among Blacks/Africans, 7,425 among Spaniards/Latin Americans and 7,390 among white men.