Corvallis, Oregon
March 25, 2009
Both plant and human diseases that
can travel with the wind have the potential to spread far more
rapidly than has been understood, according to a new study, in
findings that pose serious concerns not only for some human
diseases but also a new fungus that threatens global wheat
production.
The research, done by scientists at
Oregon State University
and other institutions, concluded that invading diseases do not
always progress in an orderly, constant rate. These historical
studies of both plant and animal diseases show that some
pathogens that can be carried through the air can actually
accelerate as they move, and can become widespread problems much
faster than had been thought possible.
"It's now becoming clear that some types of diseases can spread
more rapidly and widely than we anticipated," said Chris Mundt,
a professor of plant pathology at OSU. "This makes it especially
important, in some cases, to stop a spreading disease quickly if
you hope to stop it at all."
The studies explain, in part, how West Nile Virus spread so
rapidly across the United States when experts had been expecting
a more plodding, methodical progression of the disease. They
help analyze the progression of some historic disease problems,
such as the catastrophic potato late blight that led to the
Irish potato famine of the mid-1840s. And they suggest that a
new fungal pathogen of wheat that emerged a few years ago in
Uganda may pose a much more urgent threat to wheat production
around the world than first thought.
The research, in fact, used stripe rust of wheat, which has
spores that can spread on the wind, as a model to help explain
how this and other pathogens can move. Mundt, an international
expert on pathogens of several important food crops, has studied
stripe rust for years.
"If we didn't have crops that could resist wheat stem rust, we
pretty much wouldn't have a wheat industry," Mundt said. "From
this pathogen we've learned a lot about plant disease resistance
in general, and also how pathogens can move and spread. And this
new study confirms that it is crucial to get prepared for the
rapid spread of a new variety of wheat stem rust that appeared
in Uganda in 1999."
That new type of wheat stem rust, Mundt said, has the potential
to attack 75 percent of the world's known wheat varieties, and
in a bad year might cause up to 50 percent crop losses in some
parts of the world.
"We don't want to suggest that the sky is falling, but major
losses could occur if the right set of conditions converges,"
Mundt said. "This is something that we shouldn't take a chance
on. It's already spread to Iran, and the new research shows that
its global spread may be about to pick up speed."
People are aware of this problem, already working on it, and
hopefully they will be able to develop wheat varieties that are
more resistant to it, Mundt said.
"But our new understanding of the speed with which pathogens
such as this can spread suggest that we don't have a lot of time
to waste," he said. "If anything we should be increasing and
accelerating our work on a way to deal with this pathogen.
"This wheat disease problem could be global within a few years,"
Mundt said. "We would be foolish to ignore it."
Most plant and animal diseases that are spread by contact or
close proximity tend to move in a fairly predictable and
constant rate of speed, researchers say. However, a significant
number of pathogens can be borne by wind-carried spores or
migrating birds. In those cases, even though only small amounts
of an invading pathogen may show up at any one remote spot, it
has the potential to get a foothold and spread rapidly at this
distant location – giving the invading pathogen the ability to
literally accelerate as the epidemic spreads.
In just two years from 2004-06, the avian bird flu spread across
parts of three continents in Africa, Europe and Asia, carried by
migrating birds. From an initial source of infection in New York
City in 1999, the West Nile Virus spread across most of North
America within three years, and soon thereafter to the entire
Western Hemisphere.
The spread of these diseases seems to follow very definable
mathematical formulas, researchers found.
"It was surprising to see how closely the spread of very
different plant, animal and human diseases followed the same
mathematical relationship," Mundt said. "This is giving us a
better ability to predict how various types of diseases may
move, and hopefully prepare for them."
Though rapid transportation systems have become increasingly
important in establishing new pathogens around the globe, Mundt
said, most disease spread is still done by natural mechanisms
once a disease is established, not people getting off a jet
aircraft.
Other contributors to this research were from North Carolina
State University, the Science Applications International Corp.,
and the University of Alaska/Fairbanks. The study was supported
by the U.S. Department of Agriculture and the Ecology of
Infectious Diseases Program of the National Science Foundation
and National Institutes of Health.
The study was just published in the American Naturalist, a
professional journal.
For more background on the seriousness of the wheat stem rust
issue, editors may wish to refer to an op-ed by Nobel laureate
Norman Borlaug, published last year in the New York Times. It's
available on the web at this URL:
http://www.nytimes.com/2008/04/26/opinion/26borlaug.html?_r=1
Also, a digital image of wheat stem rust taken by Yue Jin of
USDA-ARS is available for media use, at this URL:
http://oregonstate.edu/dept/ncs/photos/wheat%20stem%20rust.JPG |
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