Will we ever conquer infection?

by David Bradley

Reporting from a Royal Society meeting on infectious diseases

The myth of a germ-free Nirvana, What is a viral infection?

Thirty years ago various experts pronounced that we had conquered infectious disease; we could thank better hygiene, sterilized food, vaccines, and antibiotics. But, in recent years there has been renewed anxiety about infectious diseases, said epidemiologist Tony McMichael of the Australia National University, Canberra.

We have been confronted with the emergence of legionnaire's disease, lyme disease, HIV/AIDS, human "mad cow" disease, ebola and hanta viruses, SARS, and many other new diseases. Old adversaries, such as tuberculosis, dengue fever, cholera, and malaria have re-emerged. Cholera is a case in point. A bacterium once confined mainly to South Asia, cholera kills thousands from Asia to Europe and from Africa to North and Latin America.


Pathogens are spreading more freely. McMichael blamed increased personal mobility, greater international trade and ever more densely populated cities. Greater poverty, changes in sexual practices, and intravenous drug use too, coupled with intensive food production and some modern medical procedures have created many new openings for evolving microbes.

Environmental changes have affected how humans come into contact with microbes while social changes, at the individual and community level ensure human networks, technology choices, politics, and the distribution of disadvantage all create new opportunities for infection.

McMichael argued that new circumstances lead to unusual contact between people and pathogens. Millions of years ago our descent from the trees exposed us to the savannah's disease-bearing insects. The advent of agriculture and civilization brought us into closer contact with animal diseases than ever before. War and invasions helped nations swap these diseases, and European expansion spread them to the New World.

McMichael proposed that we are living through a fourth transition - a global transition. Demographic, environmental, behavioural, technological, and other changes in human ecology created an environment well suited for the emergence of new diseases. Injudicious modern medicine is to blame for drug resistance in opportunistic microbes. Climate change and changes in river ecosystems are also influencing infectious disease emergence and spread.

Many factors influence the emergence of infectious diseases so what is the relative importance of environmental and social factors, asked McMichael. Having failed to achieve the germ-free Nirvana, we must recognize the increasingly globalised microbial world that will continue to produce infectious surprises. Rather than use the militaristic hyperbole of a war on microbes, we must approach the topic within an ecological framework. This will help us anticipate the effects of environmental and social change and act accordingly.

Read on... Emerging Viruses