AIDS: Science at a Crossroads

Resisting illness and infection
A small proportion of HIV positive people - perhaps 5% - appear to remain free of any damage to
their immune system or symptoms for 15 years or more. The reason for this resistance to illness is
unclear - it appears that some of these "long-term survivors" have very efficient immune
mechanisms; others seem to be infected with particularly weak strains of HIV.
A small minority of people seem to be able to resist infection with HIV. Teams of researchers have
studied people who are exposed to the virus regularly, and appear to be uninfected - for example, a
group of gay men in the US practising unprotected anal sex with multiple partners and groups of
prostitutes in Kenya and the Gambia who regularly accept clients who refuse condoms. No one knows
why the virus has not been detected among these studied groups: it could be that their immune systems
are extraordinarily efficient, or that they were exposed to an unusually weak virus which triggered their
defences. It is also possible that these people are infected, but that tests have so far failed to detect their
infection. The common finding so far is that these lucky few have very strong T cell responses to the
virus, suggesting that this is an important component of defence.
3. HIV'S GLOBAL SPREAD
HIV spreads essentially through sexual intercourse. People who have little access to information and
limited control over their circumstances are particularly at risk, especially when their sexual behaviour
is dictated by economic necessity. People who have other untreated sexually transmitted diseases,
which increase the likelihood of HIV transmission during sex, are also at greater risk. The virus has
therefore prospered in poor communities, mainly in the developing world, but also in the rich world's
deprived inner cities. Low levels of literacy and poor health care contribute to the problem.
Increasingly, as HIV spreads, it brings with it another devastating disease - tuberculosis. One-third of
the world's population is estimated to be infected with the TB bacterium but only one in 10 will ever
develop the disease under normal conditions. However, it appears that HIV infection dramatically
increases the chances of developing TB disease, from 10% in a lifetime to 8% per year. As a result,
active TB is on the increase in many parts of the world. WHO has declared TB a global health
emergency and predicts it will kill 30 million people in the coming decade - some of whom will also
be infected with HIV. Currently, an estimated 5.6 million people in the world are dually infected with
TB and HIV, according to WHO.
Who is affected?
Worldwide, at least 80% of infections are among heterosexuals. In the industrialised countries, the
majority of affected people are gay men and injecting drug users, but heterosexuals are now the fastestgrowing group at risk in these countries too. In the developing world women are becoming infected as
fast or faster than men. WHO estimates that in Africa, overall, six women now become infected for
every four men.
The extent of homosexual activity and infection in many developing countries is unknown but likely
to contribute to some degree to the total number of infections. There is evidence that men have sex with
men all over the world. Often, they will not define themselves as homosexual or bisexual. Prejudice
and legislation against homosexual activity in many countries hampers both the collection of
information on men who have sex with men, and the existence of effective prevention directed at them.
As a result, in many countries, no data exists on HIV infection and transmission through this route.
But generalised statistics belie the complexity of the global pandemic. It is in fact a string of separate
and highly varied epidemics, each influenced by local factors. For example, in Thailand, it appears that
one strain (or subtype) of HIV has been predominant among injecting drug users in Bangkok while a
very different strain has been circulating among heterosexuals in the north of the country. There is now

an overlap between the two mini-epidemics: clearly, injecting drug users also have sex.
On the other side of the world, in Edinburgh, Scotland, a short period of needle-sharing among drug
users in the early 1980s appears to have caused an explosive epidemic of HIV whose impact is still

5 - Panos Briefing: AIDS: SCIENCE AT A CROSSROADS