As people remake the world's landscapes, cutting forests, draining wetlands, building roads and dams, and pushing the margins of cities ever outward, infectious diseases are gaining new toeholds, cropping up in new places and new hosts, and posing an ever-increasing risk to human and animal health.
Writing this month (July 2004) in the journal Environmental Health Perspectives, an international team of experts warns that widespread changes in the global landscape are providing new opportunities for dozens of infectious diseases, including scourges like malaria, dengue fever, Lyme disease, yellow fever, cholera, influenza, foot and mouth, and hemorrhagic fevers.
"Evidence is mounting that deforestation and ecosystem changes have implications for the distribution of many other microorganisms, and the health of human, domestic animal and wildlife populations," according to the report compiled by the Working Group on Land Use Change and Disease Emergence, an international group of infectious disease and environmental health experts.
"Many of our current activities, primarily for economic development, have some major adverse health effects," says Jonathan A. Patz, the lead author of the report, and a University of Wisconsin-Madison professor in the Center for Sustainability and the Global Environment (SAGE) of the Nelson Institute for Environmental Studies and the department of population health sciences.
Indeed, a detailed understanding of the influence of human activities on the spread of pathogens, the report notes, is limited to only a few diseases. In the northeastern United States, for example, studies have documented that forest fragmentation, urban sprawl and the erosion of biodiversity have contributed significantly to the spread of Lyme disease.
A more global example is the AIDS virus, which scientists think may have first infected "bush meat" hunters given access to Africa's tropical forests by the growing network of logging roads in the continent's interior. The disease subsequently spread by human contact and has become a global tragedy through the ability of humans to travel the world with relative ease.
In scope, the issue is broad, affecting nearly every corner of the globe. The causes are as varied as the human activities that create the opportunities for pathogens to thrive, spread geographically and invade new hosts. It involves well-known and pervasive pathogens such as the parasite that causes malaria, a disease that claims more than 1 million lives annually, to diseases like SARS that are relatively new and, so far, limited.
"There is no single smoking gun," says Patz. "The causes are interwoven into current unsustainable development practices. "