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Read more: “Instant Expert: HIV“

AIDS was without doubt the defining epidemic of the late 20th century. Though the virus behind it was only identified in the mid-1980s, by the end of the century HIV had insinuated itself into over 36 million adults. AIDS ushered in an era of patient activism and brought money, health and politics together in ways that have changed the face of global health.

Prehistory

The exact origins of HIV are hotly debated, but genetic sequencing techniques are shedding some light on how the virus reached critical mass and began spreading around the world.

HIV-1, the most common type, is descended from a virus still found in chimpanzees living in central Africa. The earliest virus found so far was in a lymph node taken from a man in 1959 in what was then Belgian Congo. Comparing that with other early samples shows that the virus must have crossed over from chimpanzees and started to circulate and diverge in humans by the first decade of the 20th century.

HIV probably crossed the species barrier in the bloody process of butchering chimps for food. The spread of the virus in the Belgian and French colonies of central Africa in the mid-20th century was probably accelerated by rapid, male-dominated urbanisation and the concentration of labourers in camps with attendant prostitution. Health campaigns where needles were repeatedly reused may also have contributed. The links between Francophone central Africa and Haiti provided HIV with a staging post to the western hemisphere; genetic analysis suggests that the virus was imported from Haiti to the US in the late 1960s.

The sexual liberation of the 1960s and 1970s combined with homophobia concentrated large groups of sexually active gay men in small enclaves of tolerance in cities like New York and San Francisco. Anal sex is inherently more dangerous for passing on viruses than vaginal sex because it is more likely to cause small tears and lesions. That, together with a high turnover of partners, provided perfect conditions for the rapid spread of HIV. Because these men were young, otherwise healthy and largely well educated and white, their illness attracted attention in a way that earlier cases in Africa and the Caribbean had not. AIDS came out of the shadows.

A virus fit for purpose

HIV has spread so far partly because it is so good at its job. Like a computer virus that starts by knocking out anti-viral software, HIV targets the immune cells at the front line of our body’s defences. It locks onto CD4 immune cells, which usually protect us against viruses and other microbes, and inserts itself into their DNA.

When HIV first enters the body it replicates fast, causing a spike in the amount of virus present in the blood and genital fluids, known as the “viral load”. Because we recognise the virus as foreign, we begin to make antibodies. These bring down the viral load, but crucially never manage to eradicate the virus, in part because some sit quietly in the DNA of apparently healthy CD4 cells, beyond the reach of the immune system.

Over time, as the body confronts other infections, those apparently healthy cells get called up. That stirs HIV into action; the cell spews out more virus and dies. As the viral load continues to rise, the immune system becomes progressively more damaged and the number of CD4 cells falls. Other infections set in that a healthy immune system would beat easily, such as Pneumocystis carinii pneumonia. These are the opportunistic infections that make up the syndrome known as AIDS, and this is what kills people.

When first infected, most people feel mild flu-like symptoms at worst, then nothing for the nine or 10 years during which HIV typically lies latent within their immune cells.

That means people often live with the infection, and, crucially, are able to pass it on, for many years without knowing it.

A new disease

On 5 June 1981, a brief report, of monumental import, was published by the US public health agency, the Centers for Disease Control and Prevention in Atlanta, Georgia. Five gay men in Los Angeles had come down with an unusual form of pneumonia, caused by the bacterium Pneumocystis carinii, which wouldn’t normally affect healthy young adults. The CDC paper described a malfunction of the immune system that was in some way acquired sexually; it prompted a wave of similar reports from San Francisco, New York and elsewhere.

So many of the cases were in gay men that the condition was first termed GRID, for gay-related immune deficiency. But it quickly emerged that other groups of people were affected too – haemophiliacs, drug injectors, women who had had sex with affected men, their newborns and, at the time bafflingly, Haitians. In 1983 the CDC concluded that the condition, by then renamed acquired immune deficiency syndrome, or AIDS, was probably passed on by sex and exposure to blood.

By then cases of AIDS had turned up in 15 countries, largely among people in the groups already identified. But in France and Belgium immigrants from central Africa also had a condition that looked very much like AIDS. Like the Haitians in the US, these men and women were not linked with the behaviours thought to spread AIDS.

The measured tones of the CDC’s reports contrasted with a hysterical public reaction. Conservative moralists proclaimed AIDS the wages of sin, the San Francisco police force issued gloves to cops who might come into contact with people with AIDS, and the press became ever more shrill. Meanwhile US president Ronald Regan did not say the word “AIDS” until 1985 – by then more than 12,000 Americans had died.

People panicked, in part because they didn’t know what caused the illness. Though French scientists discovered a virus they thought responsible for AIDS in 1983, it wasn’t until US scientists identified the same virus a year later that the cause of AIDS was agreed to be found. In 1986 it was named human immunodeficiency virus, or HIV.

With the virus identified and screening of blood donations possible, the early hysteria began to fade. But the world’s response to HIV is, to this day, shaped by its emergence in the bathhouses and gay bars of the US.