By Kevin Loria From Business Insider

• Health officials in two Arizona counties reported that fleas tested positive forYersinia pestis, the bacteria that causes the plague.
• Plague regularly appears in the American Southwest, where it often kills rodents like prairie dogs but occasionally infects people.
• There were two human cases of the plague in New Mexico earlier this summer.

The black death is alive and well in the American Southwest.

Over the past several weeks, public health officials in two Arizona counties — Navajo County and Coconino County — have confirmed that fleas have tested positive for the Yersinia pestis bacteria, which causes thethree forms of the plague.

“Navajo County Health Department is urging the public to take precautions to reduce their risk of exposure to this serious disease, which can be present in fleas, rodents, rabbits, and predators that feed upon these animals,” the health department announced on Friday on thecounty’s Facebook page. “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.”

County officials advise against allowing pets to run free, as they could pick up infected fleas. Pets can both become infected and carry fleas that could then pass the disease onto humans.

For anyone concerned they could have been exposed, the health department added: “Symptoms of plague in humans generally appear within two to six days following exposure and include the following: fever, chills, headache, weakness, muscle pain, and swollen lymph glands (called ‘buboes’) in the groin, armpits or limbs. The disease can become septicemic (spreading throughout the bloodstream) and/or pneumonic (affecting the lungs), but is curable with proper antibiotic therapy if diagnosed and treated early.”

This isn’t an isolated incident. A couple of months ago, health-department officials in New Mexico confirmed that two residents of Santa Fe County had been hospitalized after being infected by the plague.

Why plague persists

The bacteria circulating today are still remarkably similar to those that researchers have identified as the cause of the Black Death. As theCenters for Disease Control and Prevention explains, it’s still a potentially fatal and serious bacterial illness, but now we can treat it with antibiotics, provided it’s caught early enough.

While rats and other rodents have a reputation of being carriers, it’s usually the fleas they harbor that are responsible. Plague can kill those rodents just as it can humans. In fact, one of the first signs of an outbreak is often a mass dying-off of prairie dogs or other rodents. (There was a report of a plague infection killing a squirrel in New Mexico on Thursday, according to the ProMED-mail service, which tracks disease outbreaks.)

In the US, plague bacteria tend to thrive in the hot and dry Southwest, where there are several rodents — including rats, voles, and prairie dogs — susceptible to infection. In general, the bacteria are always out there, spreading among fleas and, less frequently, rodent or other mammal populations, occasionally spilling over into humans.

Still, the US sees only a handful of cases — usually between one and 17every year. Plague is a bigger problem in places that have a harder time shutting down outbreaks. In the US, disease detectives try to find everyone an infected person came into contact with. That’s harder in regions with humanitarian crises or ongoing conflicts, according to the World Health Organization.

In the 14th century, the Black Death killed approximately 50 million people. It’s still one of the scarier infectious diseases out there, with a mortality rate of between 30% and 60% if untreated, though it’s possible to treat most cases now with antibiotics. Between 2010 and 2015, it caused 584 deaths, according to the WHO.

IMAGE: Robert Hooke’s drawing of a flea in “Micrographia,” 1665 Public Domain

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