June 1981 is the birthdate of AIDS. A short article in a medical journal described five cases of a rare form of pneumonia among previously healthy gay men from Los Angeles.Nobody could have imagined that, by 2011, thirty-two million individuals would have died of AIDS, while another thirty-three million were living with its HIV aetiological agent, the most dramatic epidemic of modern times, whose course was reviewed earlier this month by the United Nations General Assembly. How did it happen? Sadly, it was not just an extraordinary confluence of chance events, unlikely to be ever repeated, but the consequence of human interventions.
Much has been learned about the origins of HIV. Its source is the chimpanzee of central Africa, infected with an identical virus, SIVcpz. The human who started the pandemic acquired HIV during the first three decades of the 20th century while manipulating chimpanzee meat. Prior to that, for a very long time, a few other humans occasionally got infected with the chimpanzee virus, perhaps later infecting their spouses, but these remained epidemiological dead ends until two factors allowed the “patient zero” to start a chain of transmission that, from its African crucible, ultimately spread to the whole world. Even if their respective contributions will never be fully sorted out, there is little doubt that without them the pandemic would not have developed.
The first factor was the profound social changes that accompanied the European colonisation of central Africa, leading to sexual behaviours far different from those of traditional Bantu societies. In the midst of the Congo basin, the colonizers created cities where adult men outnumbered their female counterparts, up to 10-fold. Predictably, some women, who themselves had just acquired an unprecedented degree of freedom through the urbanisation process, began to trade sex against remuneration, initially with a few regular clients, and then, after 1960, with a large number of men, spreading sexually transmitted infections. This is just another example of the complex relationships between social changes and diseases. In the past century, the availability of oral contraceptives and the derepression of homosexuality also influenced the dissemination of the same pathogens. Lifestyle changes of future generations will impact on other diseases, in a way which is both unpredictable and unavoidable.
The second factor was the healthcare-related amplification of HIV through poorly sterilised syringes and needles, re-used on many patients. I had discovered this troubling aspect of African medicine when I spent four years in a district hospital of Zaire in the 1980s, struggling with a health budget of a few dollars per inhabitant per year. I belatedly understood that the same practices could have fuelled the emergence of HIV, 50 years earlier, when single-use injection material did not exist. In Cameroon, the Central African Republic and Guinea-Bissau, epidemiological studies demonstrated that patients had been infected with other blood-borne viruses (unlike HIV, compatible with a prolonged survival) during the colonial era, through unsterile syringes and needles used for the treatment of malaria, tuberculosis and sleeping sickness. The same iatrogenic mechanisms probably jump-started the HIV epidemic by increasing the number of infected humans to a level where sexual transmission could thrive. This unfortunate scenario resulted from a lag of merely fifty years between the development of therapeutic agents that required their intravenous administration and the realisation that viruses could be so transmitted.
Ultimately, the one message that the HIV epidemic should bring home is that well-intentioned human interventions can have unpredictable and disastrous microbiologic consequences. Mankind has emerged through a process of natural selection over billions of years. Apart from ourselves, there is no other living organism on earth that could destroy us completely, because if such organisms had existed, we would not have managed to reach our current status in the first place. But as I write these lines, there is renewed interest in sending humans on a wonderful voyage to Mars and back. The kids who watched Neil Armstrong’s small steps on the moon are now engineers, pilots, and politicians. They think that their own generation needs to push back a new frontier, that this is part of the human experience, perhaps something that will provide an answer to perennial questions about the meaning of life. But would it not be wiser to spend our resources and ingenuity on scientific adventures whose purpose would be to protect our earth rather than taking the risk of importing into our cherished planet a completely different form of microscopic life, perhaps not even DNA-based, whose innocuous nature has not been proven by billions of years of co-evolution with us? The AIDS tragedy should teach all scientists a lesson in prudence, and humility.