The human immunodeficiency virus (HIV) is the infective agent for acquired human immunodeficiency syndrome (AIDS). HIV is actually a group of retroviruses. Although HIV-1 and HIV-2 first arose as infections transmitted from animals to humans, or zoonoses, both are now spread among humans through sexual contact, from mother to infant, and from person to person via contaminated blood.
HIV suppresses the immune system by depleting the body of white blood cells (CD4 lymphocytes or T-helper cells). Drugs that block HIV replication in the test tube also reduce viral load and delay progression to AIDS. Where available, treatment has reduced AIDS mortality by more than 80%. If not treated, most people with HIV infection show signs of AIDS within 5-10 years. The high cost of the drugs puts these treatments out of reach for most. Due to its high rate of evolution, HIV rapidly develops drug resistance; in 2001, 75% of those receiving drug treatment were no longer protected.
Unlike many other infectious diseases, such as tuberculosis and malaria that cause illness and death in underprivileged and impoverished communities, HIV is indiscriminate about its human surroundings. However, the overwhelming majority of people with HIV—some 95% of the global total—live in the developing world. That proportion is set to grow even further as infection rates continue to rise in countries where poverty, poor health systems and limited resources for prevention and care fuel the spread of the virus and constitute formidable challenges to the control of HIV infection.
In different regions of the world HIV/AIDS shows altered patterns of spread and symptoms. In Africa, for example, HIV-infected persons are 11 times more likely to die within 5 years, and over 100 times more likely than uninfected persons to develop Kaposi's sarcoma, a cancer linked to yet another virus. As with any other chronic infection, various co-factors play a role in determining the risk of disease. Persons who are malnourished, who already suffer other infections or who are older, tend to be more susceptible to the rapid development of AIDS following HIV infection. However, none of these factors weaken the scientific evidence that HIV is the sole cause of AIDS.
HIV/AIDS is a major development crisis. Since the pandemic began, it has killed millions of adults in the prime of their lives, separated families, and destroyed and impoverished communities. More than 14 million children have been orphaned because of AIDS. In some countries, life expectancy has fallen by more than 20 years. The scale of the epidemic is causing informal social safety nets to collapse. Overall health care is declining as health services struggle with mounting demand. Workforces are being decimated and labor costs are rising, with severe consequences for investment, production and per capita income.
At the turn of the millennium, seventeen years after the start of the HIV epidemic, an estimated 34 million people worldwide were living with HIV or AIDS. By the end of 2003, the number had increased to 40 million In 2003 alone, about 5 million were newly infected and more than 3 million died. Two-thirds of those infected live in sub-Saharan Africa, and the disease is spreading quickly in other regions of the developing world-especially in the former Soviet states, the Caribbean, and parts of East and South Asia. The Joint United Nations Programme on HIV/AIDS (UNAIDS) estimates that an additional 45 million people in 126 low- and middle-income countries will become infected by 2010. A significant trend in the evolution of the epidemic is the narrowing gap between infection in the sexes as heterosexual transmission has become more common. Women are also about 10 times more vulnerable to infection by HIV during heterosexual intercourse than men, because women can contract the virus from sperm or via the blood at skin lesions, whereas men contract it only via the blood. Thus the number of infected women has increased, with a corresponding rise in the number of children born infected. There is also a difference in the incidence of different strains of the HIV virus. Sexually transmitted infections that cause genital ulcers, like syphilis or herpes appear to facilitate the transmission of the HIV virus, as an uninfected woman's chance of contracting the virus is 4 times greater if she already has some other sexually transmitted disease.