County officials are conducting additional tests and disinfecting prairie dog burrows in Picture Canyon after fleas collected in the area tested positive for plague.
The Coconino County Public Health Services District found fleas infected with Yersinia pestis, the plague, in burrows close to and adjacent to trails in the popular hiking area just north of the Wildcat Wastewater Treatment Plant in east Flagstaff.
Public health officials noticed a prairie dog burrow where animals appeared to be dying off and saw at least one dead prairie dog, said Randy Philips, division manager with the public health services district.
"It looked like something that could be associated with death due to plague," he said.
The county initially only sampled fleas over a limited area of Picture Canyon, but on Thursday health officials went back and sampled flea colonies over a much broader area, Phillips said. Results from those tests are due back today or Saturday, he said.
They also applied insecticidal dust on a small number of burrow areas on city of Flagstaff property where the infected fleas were found.
The disease is carried by rodents, rabbits and sometimes by the predators that feed on them. The disease can be transmitted to humans and other animals by the bite of an infected flea, or by direct contact with an infected animal.
September was the last time that fleas in Coconino County tested positive for plague. That was in the Doney Park area near Townsend Winona Road and Cosnino Road.
Plague in Arizona
The disease has become particularly well-established in Arizona, Colorado and New Mexico, with 80 percent of human cases found in those three states, according to Dave Engelthaler, director of programs at the genomics and pathogen research nonprofit TGen North and the former State Epidemiologist for Arizona.
Researchers believe it may be because the Southwest’s climate, topography and rodent populations are similar to the high desert grasslands of central Asia where plague first evolved, said David Wagner a professor at NAU’s Microbial Genetics and Genomics Center.
“It found a similar place to make a new home,” Wagner said.
Those that study the disease also have found that ground squirrels and rock squirrels that live in the upper desert Southwest tend to be associated with a certain type of flea species that maintains or holds onto the plague bacteria particularly well, Engelthaler said.
Those animals allow for a cycle of long-term infection to occur.
When plague spills over into prairie dog populations, it can spread quickly due to the animals’ social nature, wiping out up to 90 percent of a colony.
“If you normally see prairie dogs then next day they’re gone, there is a good chance plague is coming,” Engelthaler said. The disease’s drastic effect on the rodents make them a good indicator species for public health officials monitoring the disease.
Though plague has been heavily studied, there is still lots that scientists don’t know about the disease, Wagner said. Still poorly understood is the bacterium’s ecology, including the long-term reservoir species of the disease and where it goes between plague outbreaks.
Wagner and other researchers at the Microbial Genetics and Genomics Center are trying to find answers to some of those questions through plague research across the world. Their work includes studying the disease’s major historical outbreaks, conducting research in Madagascar, which has the world’s highest number of human plague cases, and analyzing how the disease spread from San Francisco to other places in the United States in the early 1900s.
As health officials continue to study the extent of plague-infected fleas in Picture Canyon, they are warning people to take certain precautions (see related story). Signs warning people about the potential risk are posted at area trailheads.
Symptoms of plague appear within two to six days after exposure. They include fever, chills, headache, weakness, muscle pain, swollen lymph glands in the groin, armpits or limbs.
There is no widely available vaccine for the disease but it is curable with proper antibiotics if diagnosed and treated early.