I was a medical student when the first reports of a strange new disease began to appear in the medical journals. Clusters of patients were identified with a severe wasting disease, the likes of which had never been seen before. The breakdown of the body's immune system was central to the disease process, but it was some time before scientists were able to identify a likely cause. Eventually, they discovered a new human virus called human immunodeficiency virus (HIV).
Fifteen years later, 35 million people worldwide have been infected with HIV. Fifteen million have already died from acquired immunodeficiency syndrome (AIDS) - the end result of infection with the HIV virus. The doom-laden headlines of a decade ago have disappeared, but has the AIDS epidemic gone away or not?
Until quite recently, AIDS was a fatal illness, and our approach to treating patients was akin to looking after someone with terminal cancer. With the advent of new antiviral drugs in 1996, it became possible to stop the disease in its tracks.
Dr Gerard Sheehan, consultant in infectious diseases at the Mater and Beaumont Hospitals, says that AIDS has moved from being an acute terminal illness to being a chronic disease. It is now more like diabetes, requiring regular monitoring and adjustment of therapy. Patients are quickly stabilised, and their care has moved to a predominantly outpatient setting.
The implications of these changes are huge. There are now greater demands on medical services from AIDS patients. Treatments have become more expensive and complex. The distribution of the disease has also changed, with a higher proportion of heterosexual patients, although homosexuals and intravenous drug users still form the majority.
To understand this dramatic change in the nature of AIDS, we need to look more closely at the disease and its modern treatment. The HIV virus enters the body via sexual intercourse, contaminated blood products and contaminated needles. It is a retrovirus, which means it has the ability to piggy-back onto the genetic material in the infected person's cells. This allows the HIV virus to multiply rapidly and spread throughout the body. Immune system cells called T lymphocytes are particularly susceptible to infection. As the number of T cells depletes, the immune system begins to fail and the signs and symptoms of AIDS appear.
There are now drugs which can contain the virus. One group, called transcriptase inhibitors, stops the initial takeover of the body's genetic material. Another group, called protease inhibitors, is aimed at containing the viral multiplication within the cells. Both sets of drugs are used in combination and are effective at holding new virus production in check.
The amount of circulating virus, or viral load, falls sharply with good combination drug therapy. This is checked by a blood test - a CD4 cell count. The higher the CD4 levels, the lower the viral load in the body. In the same way that doctors measure sugar levels in the blood to judge the dose of insulin needed in diabetes, so can we measure CD4 levels to assess effectiveness of AIDS drugs.
Researchers in London's Hammersmith Hospital have just come up with an even more accurate blood test to assess viral levels and the effectiveness of treatment. The Hammersmith team, working in collaboration with researchers at the University of Massachusetts, have discovered that the white blood cells of HIV-infected patients pick up a small circle of viral genetic material - a HIV "calling card". By testing for the presence of this new marker, it will be possible to monitor the effectiveness of the standard triple therapy for AIDS even more closely. Now that doctors can control the multiplication of the AIDS virus in the body, research will concentrate on further treatment improvements, as well as finding a cure. And so the "killer" element has largely disappeared from HIV infection in the Western World.
The contrast with the Third World could not be more stark. Ninety-five per cent of new AIDS cases are found in developing countries, where the vast majority of the 2.3 million annual deaths also occur. Not only must these African and Asian countries cope with underdeveloped health services, but the cost of the new AIDS drugs is completely beyond their meagre resources. Sub-Saharan Africa continues to bear the brunt of HIV and AIDS, with more than 23 million adults and children living with the disease at the end of 1999, according to the latest UNAIDS report. The UNAIDS director, Dr Peter Piot, says: "Today we see the evidence of the terrible burden women now carry in the African epidemic." His comments follow the reported findings that 55 per cent of infected adults in Sub-Saharan Africa are women.
And so, as we enter the 21st century, the story of AIDS is a story of two diseases: one a chronic, non-fatal condition in a developed world with easy access to the latest therapies, the other the "original" AIDS epidemic burning fiercely in the Third World, with death the inevitable outcome for millions of people. It's yet one more example of the dichotomy in the level of healthcare between the poor and wealthy.