Arizona Researchers Test Edible Plague Vaccine For Prairie Dogs

By Melissa Sevigny
Published: Tuesday, September 13, 2016 - 11:48am
Updated: Tuesday, September 13, 2016 - 1:54pm
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(Photo by Melissa Sevigny - KNAU)
Two young prairie dogs captured near their burrow, on Espee Ranch northwest of Williams.
(Photo by Centers for Disease Control and Prevention)

Prairie dogs are everywhere in northern Arizona — and so is the plague.

The flea-borne disease can destroy whole colonies of prairie dogs, and that has big consequences for ecosystems. Because it’s impractical to vaccinate wild animals, biologists are trying out an edible plague vaccine. It’s a tasty kibble that prairie dogs can’t resist.

The first step was figuring out what prairie dogs like to eat.

“They found in the lab that prairie dogs loved peanut butter," said Jennifer Cordova, wildlife specialist with the Arizona Game and Fish Department.

Cordova is running field trials of the first edible vaccine for sylvatic plague, the animal version of the Black Death.

“It’s really detrimental to prairie dogs,” she said. “You can have up to 100 percent mortality if plague goes through a site.”

That’s bad for all the animals that dine on prairie dogs — such as the endangered black footed ferret — and for humans who can get the plague from fleas. That’s why Cordova and a couple dozen volunteers scattered the experimental kibbles on Espee Ranch in the grasslands northwest of Williams. They’re studying two different prairie dog colonies.

“It’s a blind study,” said Cordova. “One site has a placebo and one site actually has the vaccine, and we don’t know which is which.”

The volunteers pull on rubber gloves to handle prairie dogs.  They pluck whiskers, draw blood, and comb the fur to roust out any fleas.

Nicholas Riso is one of the volunteers.

“We’re capturing these prairie dogs and testing them for fleas — we’ve been picking fleas off these guys all day — getting their blood strips, getting as much information as we can," Riso said.

That information goes to Tonie Rocke at the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wisconsin. Rocke spent 15 years inventing the edible vaccine. She said it’s dyed bright pink, “so it luminesces; you see it within a day of an animal ingesting something that has this dye in it,” she explained. “It glows where it occurs.”  

Glowing whiskers tell Rocke if the animal’s eaten the bait. She also checks the fleas and blood samples for signs of the plague.

“We’re learning a lot about plague ecology, which is another big benefit of this kind of a study,” Rocke says. “We’re definitely learning a lot more about how it’s transmitted and how animals behave in the face of an outbreak.”

Arizona’s an important test site, because plague is common here. Wildlife biologist Holly Hicks said a few years ago the disease swept through the grasslands where they’re running the experiment. One of the prairie dog colonies was left untouched.

“We figure that’s a really good sign that this vaccine is working,” Hicks says.

The edible vaccine can be quickly scattered by field researchers or even by drones. Hicks said that’s a big step toward keeping this nonnative disease in check.

“Once the prairie dogs die the fleas are just looking for the next host,” she said. “I’ve always considered the prairie dog like the canary in the coal mine. If you see a prairie dog one week and the next week there’s nothing there you know you’ve got a problem on the landscape.”

This is the fourth and final year of the field trials. Next the researchers want to find out if the vaccine will work on related animals that carry the plague, such as wood rats and rock squirrels.

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