In the 20th century, there were two unexpected outbreaks
of virally-caused disease. The influenza A pandemic of the winter
of 1918-1919 was caused by the re-emergence of an old virus, and
was responsible for the death of over 25 million people worldwide,
including 550,000 in the US. The world first became aware of another
disease outbreak in 1981, the acquired immunodeficiency syndrome
(AIDS). The catastrophic potential of this new virally-caused disease
may still not have been fully realized.
The human immunodeficiency virus (HIV) is now known
to have originated from chimpanzees.
Transmission from chimps to humans probably
occurred while animals were butchered for food in sub-Saharan
Africa, with animal blood contaminating wounds of humans. The transmission
likely passed unnoticed for a long period of time, but in the last
half of the 20th century, accompanied social upheavals led
to the outbreak of AIDS. The conditions in Africa that favored transmission
included a massive migration from rural areas to urban areas, the
breakup of family units due to the human migrations, and changes
that favored commercial sex. Increased sexual freedoms, coupled with increased global travel,
facilitated the spread of HIV into developed countries. New data suggest that the virus in chimpanzees
resulted from a recombination between
two simian immunodeficiency viruses, SIVrcm from red-capped mangabeys and SIVgsn from greater spot-nosed monkeys.
Both of these primate species are preyed on by chimpanzees.
E. Hooper in a book called, The River, suggested that early polio vaccines produced in cultures of primate cells could have been the original source of HIV.
This suggestion has made several countries wary of using polio vaccines, limiting efforts to eradicate polio. New studies now show that chimpanzees in the area that were used for early polio vaccines do not contain viruses related to HIV. In addition, the sequence studies of virus indicate
that HIV originated at least 30 years before the first polio vaccines were used. Scientists regard these results as conclusive proof that polio vaccines could not be a source of HIV.
Scope of the epidemic
People living and infected with HIV
"Over the 20 years since it was first
identified, the HIV/AIDS epidemic has continued to exceed all expectations in the severity and scale of its impact. In 1991, the then Global Programme on AIDS at the World Health Organization forecast that by 2000 the cumulative
global total of HIV infections in men, women, and children would be 40 million. In reality, this prediction has proved a serious
underestimate. An estimated 40 million people worldwide are currently living with
HIV, and some 20 million have died, giving a cumulative total number of 60 million."
In the North America, an estimated 940,000 people are infected
Through 1998, there have been 688,200 cumulative cases of AIDS and
410,800 deaths. There are an estimated 40,000 new HIV infections
per year. Between 1985 and 1998, the proportion of AIDS reported
among women and adolescent girls tripled in the US, from 7%
Facts about AIDS
(from UNAIDS 1999 World AIDS Campaign and Nature Insight review articles, Nature 410, 968 (01).)
- In some of the worst-affected countries, 2 or more out of 5 pregnant
women in urban areas are infected with HIV.
- By the end of 1997, 8.2 million children had lost their mother
to AIDS before they turned 15.
- More than 4 million children under the age of 15 have been infected.
HIV infection in children progresses more quickly to AIDS, leading
- The vulnerability of girls to HIV infection is exacerbated by denial
or neglect of their recognized human rights, including gender discrimination,
resulting in inadequate control over their exposure to sexual HIV
transmission and poor access to socioeconomic opportunities.
- Around 1/3 of the 36 million people living with HIV in the world
at the end of 1998 are young people aged 15-24.
- In 2000, 5 million people became infected with the
virus more than seven men and
women every minute of the day (14,000/day).
- In societies where the epidemic is heterosexually driven, young
women have a higher risk for exposure to HIV than young men, for
both physiological and societal reasons. This is especially true
for women dependent upon sexual relationships with men for socioeconomic
- Between 1999 and 2003, AIDS cases increased 15% for women and 1% for men in the U.S.
- Young women, either through behavior or maybe because of physiological properties of an immature genital tract have an increased risk of HIV infection.
- By the time a woman in South Africa reaches the age of 22, she has a 1 in 4 chance of being HIV infected.
- Where they have access to appropriate knowledge, skills, and means,
today's young people show a remarkable propensity to adopt safer
behaviors better than previous generations or older adults.
- In Western Europe, some 60% of young people now use condoms the
very first time they have sex.
- A study of young gay men in metropolitan areas of the U.S. found an HIV incidence of 7.2%. Less than 20% of those infected
knew of their infection. 41% practiced unsafe sex.
- Australia introduced needle and syringe exchange programs and supported changed behavioral norms on needle sharing.
HIV prevalence has been less that 0.5% in both men and women who identified themselves as injecting drug users at metropolitan
sexual health centers. The corresponding groups in Chicago and New York showed an 18-24% incidence.
- In sub-Saharan Africa, the average prevalence is 8.8% of the population between 15-49 years old.
- Education has been very effective in some countries. In Zambia, HIV prevalence for women under 20 attending antenatal clinics
in Lusaka declined from 27% in 1993 to 17% by 1999.
- Life expectancy in Africa rose from 44 years in 1950 to 59 years by the late 80s, and is now expected to return to under 45 years.
- Interventions need to be guided by evidence rather than ideology. This is nowhere more evident than in relation to sex
education for children. Evidence indicates that far from encouraging sexual activity, childhood sex education results in higher
levels of risk reduction, such as delaying the onset of sexual activity, and higher levels of condom use. Equally, a pragmatic
response to reduce disease for injecting drug users needs to attend to the increasing evidence that needle and syringe exchange
is effective in preventing HIV transmission, and has no other harmful effects.
- In the United States, as many as 50% of patients receiving antiretroviral therapy are infected with viruses that express resistance to at least one of the available antiretroviral drugs (New England Journal of Medicine 350, 1023 (2004)).