Lab work speeds plague detection
By Stephen Wampler
Public Affairs
Disappearances of prairie dog colonies in northern Arizona often signal
an outbreak of plague — even though tests have usually required seven
to 10 days to confirm the disease’s presence.
But no more. Last week, a team of Northern Arizona University researchers,
using a DNA-based detection system developed by Laboratory biomedical
scientists, confirmed the presence of plague within four hours.
The finding, by a team led by NAU microbiology professor and plague expert
Paul Keim, represents the first time the LLNL system has been used to
detect a public health disease in the environment.
"It’s very exciting, and it made all the hard work we went through
worthwhile," said Lab biomedical scientist Paula McCready. "We
did a lot of analysis to make sure these DNA signatures were unique to
Yersinia pestis (the bacteria that causes plague) and nothing else in
the environment."
Working within NAI’s Chemical and Biological National Security Program,
Lab scientists have been developing genetic signatures for the past three
years to rapidly detect the spread of infectious diseases or bioterrorist
agents.
On May 24, their work bore fruit as Keim received pages and numerous voicemail
messages from the Arizona Department of Health Services warning there
was a possible outbreak of plague in Baderville, a small community of
about 500 residents just northwest of Flagstaff.
"We were expecting an outbreak of plague," Keim said of the
disease that occurs primarily in the spring and summer months in Arizona
and New Mexico. "We had the Livermore detection methods ready to
go."
Keim’s team went into the field late Thursday and picked up samples
of fleas, which are a primary carrier of plague, at six locations within
about a one-and-a-half mile area. Using the Lab DNA signatures for plague,
the team found four positive samples by midnight, he said.
"The Livermore detection system worked well," Keim said. "For
us, it was quick and allowed us to conclude that plague was present."
Once the NAU researchers discovered positive findings of plague, they
alerted the Arizona Department of Health Services, which worked with the
Coconino County Health Department to issue a press release warning Flagstaff
area residents of the plague outbreak in the rural area.
Then Sunday, state Health Services employees and county health workers
"dusted" the prairie dog burrows where plague had been detected
with insecticide powder to kill the infected fleas, said David Engelthaler,
the Epidemic Detection and Response Program coordinator for the Arizona
Department of Health Services.
Arizona normally has one or two cases per year of humans who become infected
with plague and a handful of people have died from the disease during
the past two decades, Engelthaler said.
If promptly treated with antibiotics, the survival rate of the disease
is nearly 100 percent, Engelthaler noted. However, if the disease’s
symptoms — of high fever or heavy nausea — are not diagnosed,
a single flea bite can kill an adult.
While infected flea bites of humans represent the primary transmission
method for plague, the disease can also be contracted by contact with
infected blood or tissue of sick animals or a cat coughing on a human,
Engelthaler said.
The old testing method involved injecting a flea sample suspected of having
plague into mice. If the mice became sick and died, they were then checked
with a fluorescent antibody for plague.
With the Lab’s real-time DNA detection system, tiny samples are placed
in thin test tubes and undergo a series of rapid temperature cycles. Optical
instruments acquire a fluorescent signal from the solution, which is recorded
on a computer and translated onto a graph.
In addition to McCready, two other Lab biomedical scientists, Gary Andersen
and Lyndsay Radnedge, helped to develop the DNA signatures, assays and
screenings for plague. Their work was performed in collaboration with
the Atlanta-based Centers for Disease Control.
The Livermore DNA signatures were submitted to the CDC last summer, according
to McCready, and are in the process of being made available to U.S. public
health laboratories through the CDC.
Additionally, the Lab assays for Yersinia pestis, the bacteria that causes
plague, are now undergoing Food & Drug Administration approval for
use in determining if humans have contracted the bacteria.
DNA signatures for other pathogens, such as Bacillus anthracis (the bacteria
that causes anthrax), are being developed by researchers from LLNL, Los
Alamos National Laboratory and CDC.