Human immunodeficiency virus infection

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.

The question of the cause of AIDS was officially settled on 23 April 1984 with the announcement of the isolation of the AIDS virus. This was first called lymphadeopathy-associated virus (LAV) by its French discoverers and human T-cell leukaemia virus III (HYLV-III) by American scientists. Since 1986 it has officially been referred to as the human immunodeficiency virus (HIV). There are two known types of the virus, HIV-1, the virus involved in the initial homosexual outbreak and HIV-2, responsible for the disease in African heterosexuals, each with subtypes and up to 245 different strains which are continuously evolving. For example, HIV-1E is the variant most common in Thailand amongst heterosexuals; four subtypes of HIV1 are present in the Russian population of drug users, another in female prostitutes and another in male homosexuals. To date, no vaccine or preventative medicine has been found.

Analysis of the HIV viral family tree and mutation rates places the origin of the AIDs epidemic at around 1940 (plus or minus 10 years), nearly 20 years before the earliest known infection in humans. HIV-1 is closely related to a simian immunodeficiency virus (SIV) which infects chimpanzees. HIV-2, which is prevalent in West Africa and has spread to Europe and India, is almost indistinguishable from an SIV that infects sooty mangabey monkeys. A subspecies of chimpanzee in the African rainforest was the original source of the HIV-2 virus. The chimpanzees do not themselves suffer from any of the symptoms of HIV infection. The HIV virus could have been introduced into humans many times earlier than the starting date for the epidemic without further transmission. One scenario of the event that enabled the virus to cross the species barrier to humans is the infection of hunters butchering monkeys for meat.

HIV infection is identified in blood by detecting antibodies, gene sequences or viral isolation. These tests are as reliable as any used for detecting other virus infections. Persons who received HIV-contaminated blood or blood products develop AIDS, whereas those who received untainted or screened blood do not. Most children who develop AIDS are born to HIV-infected mothers. The higher the viral load in the mother the greater the risk of the child becoming infected.

The course of the epidemic changed over the course of the 1980s. In the 1990s, rural areas and previously low incidence countries became as infected as towns and high-incidence areas. Officially recorded cases of HIV infection in Russia and former Soviet republics were few compared with the estimated incidence, and the problem was seen to be explosive in Latin America and Asia. The transmission rates in some areas of South and Southeast Asia were as high as they a decade ago in sub-Saharan Africa.

In industrialized countries, HIV infection began to spread first in the male homosexual community and amongst intravenous drug users, disproportionately affecting males from these minority groups. In developing countries (if not initially then certainly by 1996) HIV was primarily transmitted via heterosexual sex affecting women and their children as well as men. In 1998, men accounted for two-thirds of all adults with HIV. In 1992, almost one-half of the adults infected with HIV were women—a world-wide infection rate of two a minute. At an antenatal clinic in Rwanda, a quarter of women with only one lifetime sexual partner had been infected with HIV.

In 1992, according to WHO, one person was infected with the HIV virus every 15 to 20 seconds across the world. During that year, it was estimated that 2 million people had been infected with HIV, making a total of between 10 and 12 million adults and 1 million children with the virus by the end of 1992 (one in 250 of the world's adult population, mostly between 14 and 44). Two million had developed AIDS, and of these most had died.

In 1993, over one million Indians and more than 600,000 Thais, more than 1% of the population, were estimated to be infected with HIV. In Brazil, the number of HIV-positive people in 1993 was roughly 1 million, out of a population of 150 million (0.6%). By contrast, the USA, with 225 million people, had about the same number of infected persons. Mexico had approximately 0.2-0.4% of the population infected; Colombia at least 0.6%; and Argentina at least 0.3%. (The estimate of infection rates and numbers of recorded AIDS cases in Latin America often vary because most countries have not conducted detailed surveys; it is said that 30-50% of the patients who have developed the disease are not reported. Also in China in 1995, the official incidence was 4,305 cases of HIV, but even officials admitted that the incidence could be 100,000.) The pandemic had also taken hold in North Africa and the Middle East, and in central and eastern Europe. Countries at high risk of explosive incidence included China, 11 Latin American countries, four Caribbean countries and a number of countries which had so far escaped the brunt of the epidemic, such as Indonesia, Egypt, Pakistan, Bangladesh and Nigeria. In western Europe, Spain had the highest rate of infection at 141 per million, followed by Monaco, Italy and France. Intravenous drug use was one of the chief causes in southern Europe. The situation in northern Europe is relatively stable.

During the 1990s, it was expected that more Asians would be newly infected each year than Africans (with an estimated 42% of new infections worldwide compared to 31% in Africa, 8% in Latin America and 6% in the Caribbean) and Asia would have overtaken Africa as the centre of the crisis that by the end of the millennium. For example, in the nine years since the AIDS virus first appeared in Thailand, it developed one of the world's highest infection rates (3 times that of the USA). (Thailand has two sub-strains of the more common HIV-1 virus, designated A and B. Sub-strain B is similar is similar to the virus found in Africa and is one of the most infectious strains in the world.) In 1990, world estimates of HIV infection for the year 2000 varied from 30-40 million (WHO) to as high as 120 million (including more than 10 million children), largely depending on the course of the disease in Asia.

By 1996, there had been a cumulative total of 28 million HIV cases worldwide, with 8500 people per day contracting the virus. By 1997, this estimate had been raised to 16,000 new cases a day. It was then estimated that 9.7 million people have died of AIDS since the start of the epidemic.

As of 1996 there were 13.3 million cases in sub-Saharan Africa, 4.7 million in south and south-east Asia, 1.3 million in Latin America and 1.2 million in North America, western Europe and the Pacific. In 1997, there were 4 million infected people in sub-Saharan Africa, 1.3 million in South Asia and Southeast Asia, 44,000 in North America, 47,000 in the Caribbean, and 30,000 in western Europe.

About 90% of the HIV-positive adults,and those that are newly infected, live in developing countries. While industrial countries have held HIV infection rates among their adult populations under 1 percent or less, a 1998 World Health Organization survey presented a very different picture for Africa. In Zimbabwe, for example, 26 percent of the adult population was HIV positive and anticipates that deaths due to AIDS will exceed by 30% all other deaths during the period 1980 to 2005. In Botswana the infection rate is 25 percent, Zambia 20 percent, Namibia 19 percent, and Swaziland 18 percent. In 1997, a survey of 7 armies in African countries revealed that over half of the troops are HIV positive. (These men hire prostitutes often and rarely use condoms.) Malawi, in 1997, had 30% of the urban population and 10% of the rural adult population infected with HIV. South Africa is also experiencing one of the most serious HIV epidemics in the world. In 1999, there were an estimated 3.2 million infected people in the country. 18% of sexually active adults are HIV positive (risen from around 10% in 1995). Among unskilled miners the rate of infection is more like 25%. The rate of new infections is estimated at 1,600 per day. About 9,000 children a year are born HIV positive.

Fifteen years after the first case of AIDS was reported in India, in 2001 the country had the second-largest number of HIV-infected people in the world, ranking just below South Africa. The government estimates there are 3.5 million HIV-positive Indians; the World Health Organization puts the figure at 4 million. According to various estimates, between 100,000 and 300,000 people are dying each year in India of AIDS-related illnesses. Although the nationwide rate of HIV infection remains less than 1 percent, in a country of 1 billion people, the sheer volume of cases makes India's AIDS problem costly and potentially devastating.

The world's steepest HIV curve in 1999 was recorded in the newly independent states of the former Soviet Union, where the proportion of the population living with HIV doubled between end-1997 and end-1999. In the larger region comprising the former USSR as well as the remainder of Central and Eastern Europe, UNAIDS/WHO estimated that the number of infected people would rise by a third over the course of 1999, reaching a total of 360,000. Over 2,700 cases of HIV were reported in the Russian capital in the first nine months of 1999 alone—three times as many as in all previous years combined.

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.