Malaria Transmission Peaks at Much Cooler Temperatures than Previously Predicted plus 1 more

[USGS Newsroom <oc_web@xxxxxxxx>]

Title: USGS Newsroom

Malaria Transmission Peaks at Much Cooler Temperatures than Previously Predicted plus 1 more

---

Malaria Transmission Peaks at Much Cooler Temperatures than Previously Predicted

Posted: 24 Oct 2012 12:52 PM PDT

SANTA BARBARA, Calif. — The most deadly type of malaria in humans and the one most prevalent in Africa is one that is very sensitive to climate. Previously published scientific studies put the optimal temperature for malaria transmission from mosquitos to humans at 31 degrees C (88 degrees F), but according to a new mathematical model, the temperature for peak transmission of the parasite, Plasmodium falciparum, is much, much lower. 

"Clarifying the response of malaria transmission to temperature helps us anticipate how climate change might affect disease risk," says U.S. Geological Survey parasite ecologist and senior author Kevin Lafferty. 

"This study has discovered important new temperature thresholds that govern the relationship between humans and insect-borne parasites in the environment," said USGS Director Marcia McNutt. "With hundreds of millions of cases of malaria reported in the tropics and subtropics each year, each new scientific finding brings us closer to more effectively combating this deadly disease." 

The new research shows that malaria transmission is predicted to peak at 25 degrees C (77 degrees F), and dramatically decrease above 28 degrees C (82 degrees F). The model, based on mosquito thermal physiology, incorporated published data from laboratory experiments on mosquitoes. Unlike previous models, the new model fits observations of malaria transmission in Africa very well.

 Erin Mordecai, Lafferty's doctoral student at University of California, Santa Barbara, was the lead author of USGS –led study, published in the journal "Ecology Letters." Coauthors include other scientists from UCSB, Pennsylvania State University, University of Chicago, University of California, Los Angeles, and State University of New York College of Environmental Science and Forestry. 

"We are really excited about the new findings, because they tell us temperatures as low as 82 degrees F may begin to slow malaria transmission," says Mordecai. "This study challenges the common assumption that hot temperatures simply speed up transmission." 

Malaria parasites are transmitted to humans via certain mosquito species. The new mathematical model accounts for the fact that both mosquitoes and parasites suffer under high temperatures. Previously published models typically assumed that mosquito and malaria vitality continue to increase linearly with temperature. 

To build their model, Mordecai and the research team reviewed laboratory studies that tracked the vitality and activity of malaria parasites and mosquitoes from low to high temperatures. 

Lafferty, who holds joint appointments with UCSB and the USGS Western Ecological Research Center, hopes the findings will encourage more detailed studies on how malaria parasites and their mosquito vectors behave in the field. 

"Predictive models are only as good as the data used to build them, and even ours has limitations," says coauthor Krijn Paaijmans of Penn State. "Oddly, there is little data on the response of mosquito species to temperature. Better laboratory studies and field ecology research will inform community health projects, and help them anticipate geographic shifts and seasonal shifts in malaria transmission risk." 

Sadie Ryan of SUNY-ESF added, "Looking to the future, we are now using our model to build maps of the current and potential future spatial distribution of optimal conditions for malaria transmission." 

The research was conducted as part of the Malaria and Climate Change Working Group supported by the Luce Environmental Science to Solutions Fellowship and the National Center for Ecological Analysis and Synthesis. NCEAS is supported by the National Science Foundation, UCSB and the State of California. Additional support came from NSF, USGS and the UCSB Michael J. Connell Trust. 

USGS is charged with surveying the natural resources of our Nation — including our interconnected ecosystems and how they can shape the well being of our society. The health of humans, animals — wild and domestic — and ecosystems are all inter-related, and is the concept of "One Health," which advocates understanding and appreciating the links among human, animal and ecosystem health, and the importance of and commitment to working together to address health challenges.

Not-So-Permanent Permafrost

Posted: 24 Oct 2012 09:00 AM PDT

MENLO PARK, Calif. — As much as 44 billion tons of nitrogen and 850 billion tons of carbon stored in arctic permafrost, or frozen ground, could be released into the environment as the region begins to thaw over the next century as a result of a warmer planet according to a new study led by the U.S. Geological Survey. This nitrogen and carbon are likely to impact ecosystems, the atmosphere, and water resources including rivers and lakes. For context, this is roughly the amount of carbon stored in the atmosphere today.

The release of carbon and nitrogen in permafrost could exacerbate the warming phenomenon and will impact water systems on land and offshore according to USGS scientists and their domestic and international collaborators. The previously unpublished nitrogen figure is useful for scientists who are making climate predictions with computer climate models, while the carbon estimate is consistent and gives more credence to other scientific studies with similar carbon estimates.

"This study quantifies the impact on Earth's two most important chemical cycles, carbon and nitrogen, from thawing of permafrost under future climate warming scenarios," said USGS Director Marcia McNutt. "While the permafrost of the polar latitudes may seem distant and disconnected from the daily activities of most of us, its potential to alter the planet’s habitability when destabilized is very real."

To generate the estimates, scientists studied how permafrost-affected soils, known as Gelisols, thaw under various climate scenarios. They found that all Gelisols are not alike: some Gelisols have soil materials that are very peaty, with lots of decaying organic matter that burns easily – these will impart newly thawed nitrogen into the ecosystem and atmosphere. Other Gelisols have materials that are very nutrient rich – these will impart a lot of nitrogen into the ecosystem. All Gelisols will contribute carbon dioxide and likely some methane into the atmosphere as a result of decomposition once the permafrost thaws – and these gases will contribute to warming. What was frozen for thousands of years will enter our ecosystems and atmosphere as a new contributor.

"The scientific community researching this phenomena has made these international data available for the upcoming Intergovernmental Panel on Climate Change. As permafrost receives more attention, we are sharing our data and our insights to guide those models as they portray how the land, atmosphere, and ocean interact," said study lead Jennifer Harden, USGS Research Soil Scientist.

The article "Field information links permafrost carbon to physical vulnerabilities of thawing" was published in the journal Geophysical Research Letters.

To learn more about the USGS Soil Biogeochemistry group visit their website.