After Taiwan joined the World Trade Organization in 2001, active cultivation of rice paddies fell from 80 percent to 55 percent in just three years. The government of Taiwan subsidized twice-yearly plowing of abandoned fields to reduce the spread of agricultural pests into adjacent fields still in cultivation. Compliance has been spotty. Kuo found that, while plowing did not suppress rodent populations, it did inadvertently reduce the presence of the ticks and chiggers that use rodents as their primary hosts.
"The government considers only agricultural pests such as insects and rodents. They don't think about the disease factors," said Kuo. But land use policy can have complex and unexpected reverberations in the ecology of the landscape.
Chiggers, the larval stage of trombiculid mites, spread scrub typhus (Orientia tsutsugamushi), a bacterium that gets its name from the scrubby, dense vegetation that often harbors its flesh-loving host. Scrub typhus is a common culprit underlying visits to Southeast Asian hospitals for flu-like symptoms. Without antibiotics, the infection is often fatal. Ticks (Ixodidae) transmit bacteria spotted fever group rickettsiae, causing fever, aches and rash similar to Rocky Mountain spotted fever. Neither pest prefers to live underwater.
Hualien, Kuo's study area, is one of the least populous of Taiwan's counties, yet had nearly the highest incidence of scrub typhus from 1998-2007. The county is a smattering of small villages surrounded by a patchwork of flooded, plowed, and abandoned rice paddies. Flooded paddies are poor habitat for ticks and chiggers, and so cultivation of rice, which locally means carefully managed flooding of fields to drown agricultural pests, likely suppresses ticks and chiggers as well. Even the seemingly unkillable ticks die after a few weeks of submersion, and chiggers are similarly terrestrial. Though studies are few, limited data indicate that most chiggers die after a month under water.
This study did not assess flooded paddies due to the difficulty of finding and collecting rodents, ticks, and chiggers underwater. Instead, Kuo trapped rodents in fallow and plowed fields and examined their tick and chigger passengers, testing the arachnids for presence of disease-causing rickettsial bacteria. He found 6 times as many ticks on the rodents living in fallow fields – and the proportion of infectious ticks in fallow fields was three times higher, compounding the risk. Chiggers rode rodents at a rate 3 times higher in fallow fields than plowed fields.
"This study is a great example of the kinds of indirect effects that trickle down from human policies," said Bob Parmenter, an ecologist unaffiliated with the study. "It tells a nice story about how changes in international trade barriers can have unforeseen consequences." Parmenter is director of the USDA's Scientific Services Division at Valles Caldera National Preserve near Los Alamos, New Mexico, and an expert on the influence of ecology on deadly Hantavirus outbreaks, like the current episode in Yosemite National Park (California, USA) that has infected nine visitors and killed three.
The consequences of economic pressures on land use are also present in the eastern United States, where the small farms of the eighteen and nineteenth centuries have reverted, to a large degree, to forest. With the return of deer and wildlands has come a rise in ticks, and concurrent rise in Lyme disease. Conversely, opening new land to farming or housing can bring its own disease risks.
Many studies have investigated influence of global forces on disease, said Kuo. "Most are focused on how climate change, global travel, or habitat destruction will affect the emergence of vector-borne and zoonotic disease. We show that economic organizations can actually affect human health, by influencing the landscape."Title:
Jing-Lun Huang, Pei-Yun Shu, Pei-Lung Lee, and His-Chieh Wang, Research and Diagnostic Center, Centers for Disease Control, Department of Health, Taipei, Taiwan, ROCContacts:
Liza Lester | EurekAlert!
Win-win strategies for climate and food security
02.10.2017 | International Institute for Applied Systems Analysis (IIASA)
The personality factor: How to foster the sharing of research data
06.09.2017 | ZBW – Leibniz-Informationszentrum Wirtschaft
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research