Public health officials in Arizona say fleas collected in Picture Canyon, a popular hiking area northeast of Flagstaff, have tested positive for bubonic plague. An infectious disease once fatal to most humans, plague is caused by the Yersinia pestis bacteria.

“Plague is not common east of the Mississippi, but it commonly occurs west of the Mississippi,” Marlene Gaither, environmental health program manager for Coconino County Public Health Services District (CCPHSD), told Medical Daily. What is unusual, then, is not the occurrence of plague in northern Arizona, but the fact that plague, which is enzootic — endemic in animals — occurs in the rodent population only above 4,500 feet in this southwestern state.

Asked why this is so, Gaither laughed. “Your guess is as good as anyone’s,” she said. “The environment, the rodent population, possibly the season may explain this, but so far nobody … I haven’t seen any scientific study that explains why in Arizona it only exists above 4,500 feet.”

Now that plague has been confirmed, the County has begun to warn the public in part by flagging infected burrows, yet also by warning people to de-flea their pets. Cats are sensitive to plague and become sick, but dogs do not succumb to the disease themselves. In either case, dogs and cats both carry fleas that, if infected, may spread the plague to their owners and others. Infected, we humans will develop a high fever, headache, and weakness, while one (or more) of our lymph nodes, called buboes, may swell painfully.

Rather than being forced to react or respond to plague incidents in humans, the idea is to “keep it in the animal population,” Gaither said. “It’s about prevention.” Certainly, plague is easily treated with antibiotics, but patients can become very sick if not attended after first showing signs of illness.

How does surveillance work?

“We found the perfect rodent population to monitor for plague — prairie dogs,” Gaither told Medical Daily. While prairie dogs typically live near or around residents, they also colonize in pretty good-sized groups. “The one unique thing to them is they are highly sensitive to plague,” she said. “One day you see them, and the next, where did they go?” In other words, when a prairie dog colony is hit by plague, they die off pretty quickly.  At this point, public health officials who actively monitor the population of colonies will notice a sudden drop in rodent numbers and so begin the process of capturing animals and testing fleas. In some cases, it is a community member who notices the sudden disappearance of prairie dogs and raises the alarm.

“In the past — I’ve been living in the county for 32 years — we saw plague occur every five years,” Gaither said. In recent years, though, health officials have been finding it more frequently. “Every other year, or back to back. But we look every year for it,” she said. Gaither believes this is a positive sign of better surveillance.

The Center for Microbial Genetics and Genomics at Northern Arizona University conducted the tests on behalf of the county, an act of generosity, says Gaither, because these DNA tests are quite expensive. Possibly due to warmer temperatures, the plague infestation occurred earlier than usual this year; typically the season is late summer. “It’s been unusually warm and dry here in northern Arizona. March was unusually warm,” Gaither said.

The Coconino County health department urges people who live, work, or visit areas of plague to take these precautions:

  • Do not handle sick or dead animals
  • De-flea pets routinely, prevent them from roaming loose
  • Avoid rodent burrows and fleas 
  • Use insect repellents when visiting or working in areas of active plague 
  • Wear rubber gloves and other protection when cleaning and skinning wild animals 
  • Do not camp next to rodent burrows and do not sleep directly on the ground
  • Take any sick cat directly to a veterinarian for proper diagnosis and treatment
  • See your physician immediately if you become sick or feverish 

“A lot of people ask why don’t we get rid of prairie dogs so we’d get rid of the plague, but it doesn’t work that way,” Gaither said. The pesky bacteria simply would migrate to another animal group. At least for now, the pretty prairie dogs, though relentlessly pursued by fleas, remain safe from humans.