Lab work speeds plague detection
By Stephen Wampler
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.