It is projected that sometime this year, a child's birth will tip the ratio of people living in cities to more than half the world's population for the first time. That tipping point worries Lord Robert May, who heads the mathematical biology research group in the zoology department at Oxford University.
May predicted that there will be new and reemerging infections from the combination of ever denser cities and a growing wave of unregulated trade in animal meat called bushmeat. He spoke at an October 5 seminar on infectious diseases and millennium development goals. The talk was held at the Broad Institute of MIT/Harvard in Cambridge and co-sponsored by the HSPH Office of the Dean and the Harvard Initiative for Global Health's 'Global Infectious Diseases Program.'
Since the advent of agriculture, permanent settlement, and the growth of cities, most bacterial and viral scourges that have attacked people have come from animals, especially domestic, with whom humans share 296 diseases, said May, citing the book Cities, by John Reader. The most recent suspected links have been HIV/AIDS from primates, SARS from civets, and avian flu from ducks and pigs.
The imminent threat could roll back the major gains in life expectancy achieved for people in both developed and developing countries in the last 50 years, May suggested. "The poorest countries today are doing better than [is] the developing world at comparable levels of development 50 years ago," May said. "[Yet] the bad news is that there is still a very large gap between diseases of the rich and poor."
Infectious diseases account for 57 percent of the disease burden of low-income countries, an order of magnitude higher than the seven percent of high-income countries, as measured by disability adjusted life years, or DALYs, he said. (One DALY equals one year of healthy life lost.) That has led some people to believe that infectious diseases are no longer a worry and that vaccines for polio, measles, and other diseases are no longer necessary.
"My candidate for one of the most stupid things anyone has ever said - and there is quite a bit of competition - is W.H. Stewart, in the 1967 U.S. Surgeon General's report, 'The time has come to close the book on infectious diseases,'" May said. "You can make catalogues of diseases for which 99 percent of the global burden falls outside [economically developed] countries," he said.
Most prominent among the diseases is HIV/AIDS, a pandemic predicted in the mid-1980s by May and colleague Roy Anderson. The World Health Organization and others criticized their 30-year projection as too gloomy.
Now, most of the research and money for diseases in the developing world is directed toward the "big three" - HIV/AIDS, malaria, and TB. Less fashionable diseases likely affect just as many people, he said, many of which are better addressed with more immediate potential preventive agents and therapeutics.
Complicating matters further, ideology is trumping the single most effective agent to prevent the spread of HIV/AIDS: condoms. "Many of the people wishing to do good things are involved with faith-based belief systems that clash directly with their primary aims," said May.
Financial incentives, especially advance guarantee purchase of a drug at a suitable price, are important, but they miss the bigger picture, he asserted, because they fail to shed light on pathogenesis.
"The premise is wrong," May said. "We have such a brilliant molecular understanding of HIV and its interaction with the immune system cells that we can actually design, as a result of our descriptive understanding, drugs that can keep people with HIV alive. Most people who work on HIV don't even realize that we don't have an understanding of the pathogenesis of AIDS. There is no agreement about how HIV eventually causes the immune system to collapse."
The solution for a successful HIV vaccine and the bigger challenge of cracking the problem of how the immune system works lie in the same rational fact-based science responsible for improving the overall health of the world so far, he said.
Aspects of May's talk were published online on September 26 in Trends in Ecology and Evolution. Other details may be found in his 2005 anniversary address to the Royal Society in print and video.
—CCM
Copyright, 2009, President and Fellows of Harvard College
