麻豆传媒

Read more: 鈥�Instant Expert: HIV鈥�

The development of powerful drug regimens that can virtually eliminate HIV replication is arguably one of medicine鈥檚 greatest success stories; an HIV infection no longer has to be a death sentence. But infection rates are still breathtakingly high in many parts of Africa, reaching over 15 per cent of adults in countries such as South Africa and Zimbabwe. Now the challenge is to fund drug treatment for all who need it while cutting the number of new infections.

Politics of aids

The early history of AIDS has shaped perception and treatment of today鈥檚 epidemic in important ways. It emerged among gay men, who were widely regarded as immoral by the homophobic majority in the US. The addition of prostitutes and heroin addicts to the list of high-risk groups did little to increase public sympathy, so at first funding for prevention and care remained scarce.

To reduce discrimination against people with HIV and to try and stop it spreading, activists and many in the public health establishment tried to create a sense of shared risk: the mantra was 鈥淎nyone can get HIV鈥�. When the epidemic took off among straight people in Africa, the difficulty of confronting the different patterns of sexual relationships became clear. So people working in the HIV industry took the spotlight off the controversial issues of sex and drugs by emphasising the social dimensions of the epidemic. It was packaged as a problem not so much of unprotected sex but of underdevelopment, poverty, gender inequality, human rights and much else.

The strategy certainly brought in more cash: funding for HIV prevention and treatment in developing countries ballooned from under $250 million a year in the early 1990s to some $18 billion last year. Ironically, it also made it harder to spend money where it might be most effective, in programmes that provide clean needles to drug users, or that provide sexual health services to people most at risk.

Governments that didn鈥檛 want to engage with the messy realities of sex and drugs chose more politically popular approaches, such as stopping transmission from mother to child, care for orphans, and treatment programmes. In the mid-1990s, an estimated 2.5 million people a year became infected with HIV. A decade and a half later we have over 70 times as much cash available for prevention and care, but only a small fraction of it is spent on programmes that directly reduce the likelihood of an infected person passing on body fluids to someone else. Perhaps unsurprisingly, then, this year another 2.5 million people will be infected with HIV worldwide.

Two epidemics

The global HIV epidemic used to be treated as if it were a single entity that played out the same way across the world. It鈥檚 now clear that sub-Saharan Africa has a different pattern of infections to other countries.

In the west and most of the developing world outside sub-Saharan Africa, HIV remains largely confined to certain groups 鈥� namely drug injectors, gay men and prostitutes 鈥� in what are sometimes termed 鈥渃oncentrated epidemics鈥�. That鈥檚 because HIV is a hard virus to catch sexually, and people are more likely to pass it on in the first few weeks after infection, when their viral load is highest (see graph). HIV will thus spread fastest through groups where people have unprotected sex with more than one partner in a short period 鈥� mainly prostitutes and gay men on the party scene. In most of the world, as a broad generalisation, straight men and women tend to practise serial monogamy.

In the second pattern, common in east and southern Africa and some parts of west Africa and the Caribbean, HIV has spread deep into the general population, in a so-called 鈥済eneralised epidemic鈥�. Infection rates can be about 10 per cent of the straight population or in some areas even higher. That鈥檚 because in these countries both men and women are more likely to have a small number of concurrent long-term partners with whom they have sex regularly, perhaps because of a legacy of polygamy and freedom of movement for both sexes.

Infection may initially have risen fastest among sex workers and their clients, but those men then had sex with several other regular partners while still highly infectious. Since some of those newly infected women also had multiple partners, HIV was soon carried deep into the general population.

Outside of sub-Saharan Africa, people in high-risk groups do sometimes pass the virus on to partners who don鈥檛 themselves trade sex or have gay sex. But where serial monogamy is the norm, those people will probably not then have sex with someone else until the early, highly infectious period has passed. So they are less likely to pass the virus to straight partners.

Life-saving drugs

From the time the virus was identified, HIV and AIDS were talked about almost interchangeably, since the first inevitably led to the second, with a time lag of about 10 years. Then in 1995, researchers showed that drug treatment could put the brakes on HIV replication, causing the amount of virus in someone鈥檚 blood and bodily fluids to plummet to undetectable levels.

The first medicines had nasty side effects, such as nerve damage and severe diarrhoea, and involved complicated dosing regimens of up to 20 pills a day. Nowadays, people start treatment with just one or two tablets a day, and any side-effects are less dire. People who are HIV-positive can stay healthy for several decades if they scrupulously take their medicines. They seem to have slightly higher rates of osteoporosis, dementia and liver damage, but these problems pale by comparison with full-blown AIDS. Where the drugs are affordable, HIV has been transformed from an inevitably fatal infection to a manageable, life-long condition comparable to diabetes.

But as AIDS 鈥� the visible face of HIV 鈥� disappears, the incentive to limit sexual partners and use condoms is evaporating. This is probably why new infections are rising among gay men in many western countries.