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Changing landscape could promote disease
Two major research reports, one on climate change the other on development practice, have both suggested that radical changes to the landscape are increasing the risk of infectious disease.
One of the reports by a team of American and French scientists says there is mounting evidence that global warming will see the movement of disease-causing micro-organisms away from their current concentration in the Tropics to other parts of the world.
The second report, from an international group specialising in environmental health, says that accelerating changes to the world's landscape - like cutting forests, draining wetlands, road building and urban sprawl - have allowed infectious diseases to gain new toeholds.
They say dozens of diseases like malaria, dengue fever, Lyme disease, yellow fever, cholera, influenza, foot and mouth, and haemorrhagic fevers, are all now appearing in new places with new hosts and posing an ever-increasing risk to human and animal health.
The report on disease and climate change is the work of three scientists, Vanina Guernier, Michael Hochberg, and Jean-François Guegan who have been compiling epidemiological data on 332 difference human pathogens across 224 countries. They have just published their findings in the Public Library of Science journal, PloS Biology.
"Our results show that climatic factors are of primary importance in explaining the occurrence and diversity of human pathogens, suggesting that global climate change might have cascading effects regarding the risks of PIDs (parasitic and infectious diseases)," they write.
"For instance, if specific temperate areas were to become more tropical, our results suggest that PID species and their associated vectors/reservoirs would be likely to colonise these changed areas."
(Vectors are the insects or ticks that transmit the micro-organisms to humans or animals. For example, a mosquito is the vector that carries the malaria parasite.)
The scientists say their studies also suggest that previous research has probably "substantially underestimated just how many different pathogens there are in the world.
"Based on a single host species, humans, we estimate that true tropical pathogen species diversity is greater than current estimates by a factor of about 22 in the Northern Hemisphere and about 37 in the Southern Hemi-sphere," they write.
"If our work is representative of other (host) species, diversity may be currently underestimated by more than an order of magnitude, and based on our findings, this differential should increase as one goes from temperate to tropical latitudes."
The report on landscape and disease is the work of the Working Group on Landscape Use Change and Disease Emergence who have just published their findings in the journal, Environmental Health Perspectives.
According to Professor Jonathan Patz, lead author of the report, and heads of the Center for Sustainability and the Global Environment (SAGE) at University of Wisconsin-Madison, much of the world's economic development has major adverse health effects.
But he says currently there is only limited understanding of how human activity helps spread pathogens.
"In the north-eastern 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," he said in a media statement.
"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."
The group's report makes a series of recommendations to address the issue, including linking land use to public health policy, expanding research on deforestation and infectious disease, the development of policies to reduce "pathogen pollution," and the establishment of centres for research and training in ecology and health research.
"While there are many health crises around the world today, there are ongoing human activities that threaten natural resources key to sustaining the health of future generations," says Patz.
"We need to look at the root causes of the spread of infectious disease, and many of these are related to habitat and ecosystem change."
