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Study: Ecosystem alterations leading to widespread human health impacts

Research consortium proposes systematic assessment approach

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In Belize, agricultural runoff is changing lowland wetlands to favor a proliferation of mosquitoes that are efficient malaria vectors. bberwyn photo.

By Bob Berwyn

FRISCO — The accelerating pace of human-caused changes to natural systems may threaten the Earth’s ability to sustain a growing population at a fundamental level, a team of researchers said in a new paper published last week in the Proceedings of the National Academy of Sciences.

The paper describes a new branch of environmental health that focuses on the public health risks of human-caused changes to Earth’s natural systems. Researchers contributing to the paper work with the Health & Ecosystems: Analysis of Linkages consortium.

The approach differs from the classic discipline of environmental health, which focuses on micro-level impacts — for example, how changes in the home environment can affect the health of an individual or a family, said Dr. Samuel Myers, a research scientist in the Department of Environmental Health at Harvard School of Public Health.

“That has almost nothing to do with the changes in structure of ecosystems … We’re trying to distinguish our area, which is much broader,” Myers said. “The  starting point is, human activity is changing systems, and those changes are accelerating.”

Human activities are altering the planet’s land cover, rivers and oceans, climate, and the full range of complex ecological relationships and biogeochemical cycles that have long sustained life on Earth, Myers explained.

“In  that context, it’s important to start investigating, what are the implications … The underlying construct is that people obtain really important benefits from functioning ecosystems,” he said.

The HEAL paper lays out a framework for this new field.

“We’ve nibbled around the edges of this, but we need a comprehensive robust discipline,” he said, adding that the brunt of the burden will be borne by poor people, making this a global moral and environmental justice issue.

The paper lists some of the ways the alteration of ecosystems is already affecting human health on several different levels.

For example:

  • In parts of Africa, forest cutting also alters the composition and density of aquatic snail species in a manner that favors transmission of schistosomiasis;
  • In Belize, nutrient enrichment from agricultural runoff hundreds of miles upstream changes vegetation patterns of lowland wetlands that favors the more efficient malaria vector Anopheles vestipennis over the less efficient vector Anopheles albimanus, leading to increased malaria exposure among coastal populations.

The authors also explain that landscape/ecosystem alterations can also change human-wildlife interactions — and that can lead to the proliferation of zoonotic disease (diseases that can be shared by, or jump from, animals to humans).

“There is compelling evidence that these mechanisms played the central role in initial outbreaks of HIV and Ebola virus, as well as several lesser-known zoonoses,” the authors wrote, adding that about 75 percent of emerging infectious diseases can potentially be traced to the same mechanisms.

Myers said the loss of wildlife can have a direct impact by changing the intake of both micro- and macronutrients among indigenous people. Some of his recent research in Madagascar has focused on this area. That, in turn, can lead to malnutrition, which makes people more susceptible to other illnesses, or even direct starvation, he said.

“If households in a population in Madagascar were unable to harvest wild meat for consumption, their children would experience a 30% higher risk of iron deficiency anemia — a condition that increases the risk for sickness and death from infectious disease, reduces IQ and learning, and reduces lifelong capacity for physical activity,” the authors wrote.

“There is growing awareness that dwindling populations of marine and terrestrial wildlife may represent a nutritional crisis for many people who cannot readily replace these foods with domesticated species or fortified foods.”

In the rich countries of the developed world, the loss of natural food sources and declining ecosystems may not be a big deal for consumers, who can rely on market-based and engineered solutions (imported or mass-produced food).

But in the less-developed world, the loss of of ecosystem services is a growing environmental health disaster.

Bringing the lesson a little closer to home, Myers said there’s strong evidence that risk of West Nile virus exposure in the United States rises as avian biodiversity falls. Similarly, Lyme disease exposure increases with falling mammalian diversity.

Overall, there is plenty of evidence that “nearly every dimension of human health is being affected, and it is likely that the disease burden associated with these aggregate ecosystem alterations is large and growing,” the researchers concluded, proposing a more system-atic and comprehensive approach to understanding the health impacts of ecosystem alteration.

Such a framework would help better inform decision-making, land-use planning, environmental conservation, and public health policy realms.

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