nsf.gov - News - Infectious diseases and climate change intersect with no simple answers

Study highlights challenges of predicting disease outcomes in a warming world.

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Monarch butterflies carry infections in parts of the U.S. where they breed year-round. Credit: P. Davis and S. Altizer Download the high-resolution JPG version of the image. (445 KB)

Biologist studying tumors on coral; climate warming may fuel lethal coral diseases. Credit: B. Willis

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Muskoxen may be susceptible to arctic climate change and emerging infectious diseases. Credit: S. Kutz Download the high-resolution JPG version of the image. (1.3 MB)

White-footed mice: the primary reservoir hosts for Lyme disease in the eastern United States. Credit: R. Ostfeld

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Black-legged ticks, the primary vectors of Lyme disease in the northeastern United States. Credit: K. Oggenfuss

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The researchers' findings are described in the Aug. 2, 2013, issue of Science. Credit: Copyright AAAS 2013

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Climate change is already affecting the spread of infectious diseases--and human health and biodiversity worldwide--according to disease ecologists reporting research results in this week's issue of the journal Science.

Modeling disease outcomes from host and parasite responses to climate variables, they say, could help public health officials and environmental managers address the challenges posed by the changing landscape of infectious disease.

"Earth's changing climate and the global spread of infectious diseases are threatening human health, agriculture and wildlife," said Sam Scheiner, National Science Foundation (NSF) program director for the joint NSF-National Institutes of Health Ecology and Evolution of Infectious Diseases Program, which funded the research.

"Solving these problems requires a comprehensive approach that unites scientists from biology, the geosciences and the social sciences."

According to lead author Sonia Altizer of the University of Georgia, the issue of climate change and disease has provoked intense debate over the last decade, particularly in the case of diseases that affect humans.

In the Science paper, Altizer and her colleagues--Richard Ostfeld of the Cary Institute of Ecosystem Studies; Pieter Johnson of the University of Colorado; Susan Kutz of the University of Calgary and Canadian Cooperative Wildlife Health Centre; and Drew Harvell of Cornell University--laid out an agenda for future research and action.

"For a lot of human diseases, responses to climate change depend on the wealth of nations, healthcare infrastructure, and the ability to take mitigating measures," Altizer said.

"The climate signal, in many cases, is hard to tease apart from other factors like vector control, and vaccine and drug availability."

In diseases affecting wildlife and agricultural ecosystems, however, findings show that climate warming is already causing changes.

"In many cases, we're seeing an increase in disease and parasitism," Altizer said. "But the effect of climate change on these disease relationships depends on the physiology of the organisms and on the structure of natural communities."

At the organism level, climate change can alter the physiology of parasites. Some of the clearest examples are found in the Arctic, where temperatures are rising rapidly. Parasites are developing faster as a result. A lungworm that affects muskoxen, for instance, may be transmitted over a longer period each summer, making it a more serious problem for the populations it infects.

Climate change is also affecting entire plant and animal communities.

Community-level responses to rising temperatures are evident in tropical marine environments such as the coral reef ecosystems of the Caribbean. Warmer water temperatures have directly stressed corals and facilitated infections by pathogenic fungi and bacteria. When corals succumb, other species that depend on them are affected.

The potential consequences of these changes are serious. The combination of warmer temperatures and altered disease patterns is placing growing numbers of species at risk of extinction, the scientists say.

In human health, there is a direct risk from pathogens like dengue, malaria and cholera. All are linked to warmer temperatures.

Indirect risks also exist in threats to agricultural systems and game species that are crucial for subsistence and cultural activities.

The scientists recommend building on and expanding data on the physiological responses of hosts and parasites to temperature change. Those mechanisms may offer clues to how a system will respond to climate warming.

"We'd like to be able to predict, for example, that if the climate warms by a certain amount, then in a particular host-parasite system we might see an increase from one to two disease transmission cycles each year," Altizer said.

"But we'd also like to try to tie these predictions to actions that might be taken."

Some of those actions might involve more monitoring and surveillance, adjusting the timing of vector control measures and adopting new management measures.

These could include, for instance, closing coral reefs to human activity if a disease outbreak is predicted, or changing the planting strategy for crops to compensate for unusually high risks of certain diseases.

The researchers also point out that certain local human communities, such as those of indigenous peoples in the Arctic, could be disproportionately affected by climate-disease interactions.

Predicting where these local-scale effects might be most intense would allow societies to take measures to address issues such as health and food security.

"Involving local communities in disease surveillance," said Altizer, "could become essential."

-NSF-

Media Contacts Cheryl Dybas, NSF (703) 292-7734

cdybas@nsf.gov
Beth Gavrilles, University of Georgia (706) 542-7247

 bethgav@uga.edu
Lori Quillen, Cary Institute of Ecosystem Studies (845) 677-7600

 quillenl@caryinstitute.org
Jim Scott, University of Colorado Boulder (303) 492-7531

jim.scott@colorado.edu
John Carberry, Cornell University (607) 255-5353

 johncarberry@cornell.edu

Related WebsitesNSF Special Report: The Ecology and Evolution of Infectious Diseases:

 http://www.nsf.gov/news/special_reports/ecoinf/index.jsp
NSF News: Controlling the Spread of Diseases Among Humans, Other Animals and the Environment:

http://www.nsf.gov/news/news_summ.jsp?cntn_id=125496
NSF Discovery Article Series: Ecology and Evolution of Infectious Diseases:

 http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=127103&org=NSF

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2012, its budget was $7.0 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives about 50,000 competitive requests for funding, and makes about 11,500 new funding awards. NSF also awards about $593 million in professional and service contracts yearly.

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Guillermo Gonzalo Sánchez Achutegui

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nsf.gov - Discovery - Snails in the Waters, Disease in the Villages

Treatment for snail-borne schistosomiasis works best over the long haul.-

 Monitoring for infectious snails in bodies of water near villages in coastal Kenya.
Credit: J. Clennon, Emory University
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Countries worldwide where people are at risk for the snail-borne disease schistosomiasis.
Credit: CDC
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People who work in rice fields are exposed for many hours to snail-infested waters.
Credit: U. Kitron, Emory University
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GIS map showing four communities in Kenya that are at high risk for schistosomiasis.
Credit: Charles King, Case Western Reserve University et al.
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 Diagnosis of schistosomiasis is made by detection of parasite eggs in urine samples.
Credit: C. King, Case Western Reserve University
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 Bulk containers of cans of pills of the anti-schistosomiasis drug praziquantel.
Credit: F. Richards, Carter Center
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Watch where you jump in for a swim or where your bath water comes from, especially if you live in Africa, Asia or South America. Snails that live in tropical freshwater in these locations are intermediaries between disease-causing parasitic worms and humans.

People in developing countries who don't have access to clean water and good sanitation facilities are often exposed to the infected snails. Then they're left open to the parasitic worms.

The worms' infectious larvae emerge from the snails, cruise in shallow water, easily penetrate human skin and mature in internal organs.

The result is schistosomiasis, the second most socioeconomically devastating disease after malaria. As of 2009, 74 developing nations had identified significant rates of schistosomiasis in human populations.

There has been much debate about how best to prevent the disease, says Charles King, a physician and researcher at Case Western Reserve University in Cleveland, Ohio. "Beyond that," he asks, "how long should treatment last once someone has schistosomiasis?"

"Current guidelines focus on suppressing the disease's effects by limiting the infection during childhood," says King. "But that may not be enough to cure it or to prevent re-infection, leaving children still at risk for stunted growth and anemia."

King and colleagues recently published results of a study of long-term treatment of schistosomiasis in the journal PLOS Neglected Tropical Diseases.

The team's work is funded by the National Science Foundation (NSF)-National Institutes of Health (NIH) Evolution and Ecology of Infectious Diseases (EEID) program.

At NSF, the EEID program is supported by the Directorate for Biological Sciences and Directorate for Geosciences. At NIH, it's supported through the Fogarty International Center.

Schistosomiasis is usually treated with a single dose of the oral drug praziquantel.

World Health Organization (WHO) guidelines set forth in 2006 recommend that when a village reports that more than 50 percent of its children have parasite eggs in their urine or stool--a clear sign of schistosomiasis--everyone in the village should receive treatment.

When 10 to 50 percent of children are affected, say the guidelines, only school-age children should be treated--every two years. With less than 10 percent, mass treatment is not suggested.

But because of the long-term health effects of schistosomiasis, says King, "we now think it's better to provide regular yearly treatment."

He and scientists Xiaoxia Wang, David Gurarie and Peter Mungai of Case Western Reserve University; Eric Muchiri of the Ministry of Public Health and Sanitation in Nairobi, Kenya; and Uriel Kitron of Emory University in Atlanta, Georgia, used data collected in 10 villages in southeastern Kenya to run advanced models of village-level schistosomiasis transmission.

They scored the number of years each of the 10 villages would be projected to remain below a 10 percent infection level during a simulated 10-to-20-year treatment program.

All strategies that included an initial four annual treatments reduced community prevalence of the disease to less than 10 percent. Programs with gaps in treatment, however, didn't reach this objective in half the villages.

At typical levels of treatment, the researchers found, current WHO recommendations likely could not achieve full suppression of schistosomiasis.

"With more aggressive annual intervention that lasts at least four years," says King, "some communities might be able to continue without further treatment for 8 to 10 years.

"But in higher-risk villages, repeated annual treatment may be necessary for an indefinite period--until the eco-social factors that foster the disease [such as poor wastewater treatment] are removed."

In high-risk places, ongoing surveillance for the disease and annual drug treatment, the scientists say, need to become the mainstays of control.

In short, these villages require what they call "re-worming after de-worming."

But what happens if townspeople move to a more arid location, one with less freshwater and fewer snails?

In drier landscapes, schistosomiasis is a rare event that happens only during floods. Response to treatment therefore may be much better. Unless or until another flood occurs.

Although drier locales carry less risk for the disease, they're by no means free and clear. Even in arid locations, people would likely need to be treated more than once to get rid of the parasites.

"This research demonstrates the value of understanding where disease-causing organisms are in the environment," says Sam Scheiner, NSF program officer for EEID.

"Such knowledge can reduce human diseases much more effectively and at a lower cost than simply focusing on treatment."

The best goal, says King, is complete eradication of schistosomiasis.

To achieve that, scientists need to determine what makes a "wormy village," how often therapy is needed to prevent disease in such locations--and what can be done to change the environment such that a high-risk village becomes a low-risk one.

Related Websites
NSF Special Report: Ecology and Evolution of Infectious Diseases: 

http://www.nsf.gov/news/special_reports/ecoinf/index.jsp
NSF News Release: Controlling the Spread of Diseases Among Humans, Other Animals and the Environment:

 http://www.nsf.gov/news/news_summ.jsp?cntn_id=125496

 The National Science Foundation (NSF).

Guillermo Gonzalo Sánchez Achutegui

ayabaca@gmail.com

ayabaca@hotmail.com

ayabaca@yahoo.com

 Inscríbete en el Foro del blog y participa : A Vuelo De Un Quinde - El Foro!