As the world is grappling with the coronavirus pandemic, the World Health Organization has warned that another infamous killer–the bubonic plague–has made a comeback by categorizing it as a re-emerging disease. As CNN reported, on July 7, Chinese authorities confirmed a case of the bubonic plague in inner Mongolia. and yesterday in an unrelated case, a 15-year-old Mongolian boy died of the plague after eating an infected marmot, the country’s health ministry announced.

And while cases of bubonic plague are not uncommon in rodents around the world, yesterday it was confirmed that a squirrel in Colorado tested positive for the disease. Overall, there are approximately 1,000 to 2,000 cases every year, but that is likely a modest figure as there are a number of unreported cases, according to the WHO.

Why This Matters: As USA Today wrote, cases of the plague are rare. In the U.S., most plague cases occur in the Southwest, including in New Mexico, Arizona, and Colorado. Advances in medicine mean we’re far more equipped to deal with bubonic plague in 2020 than we were in the Middle Ages, but it can turn into pneumonic plague if left untreated because the bacteria can move to the lungs. Both COVID-19 and bubonic plague result from the proximity of humans to animals and can be transmitted to humans through deforestation and animal habitat loss. It’s one more reminder that our health is reliant upon the health of our planet.

Colorado Case: As ABC News reported, Jefferson County, CO Public Health said in its statement that household pets can be susceptible to plague infection which could transfer to humans if they pick up infected fleas.

“Cats are highly susceptible to plague and may die if not treated promptly with antibiotics. Cats can contract plague from flea bites, a rodent scratch/bite or ingestion of a rodent. Dogs are not as susceptible to plague; however, they may pick up and carry plague-infected rodent fleas,” the department said in a statement.