If reports of measles and whooping cough making a reappearance aren't alarming enough, the news that three people in New Mexico have contracted plague this year might have you on edge. But these aren't the only recent cases of plague in the state—the disease appeared in both 2016 and 2015, causing one death—or even in the U.S.
In 2015, a child contracted the plague in Yosemite National Park, and so did a tourist from Georgia; park officials closed a campground where they discovered two dead squirrels infected with the disease. That same year in Colorado, a pitbull infected four humans with pneumonic plague before being put down, and two other Colorado residents died from plague, including a 16-year-old boy.
It all seems very scary, but don't go sealing yourself in protective gear yet. There's less to fear about plague than you may think. While the public is prone to panic that a medieval illness, which wiped out a quarter of Europe in the Middle Ages during the Black Death, has suddenly arisen from obscurity, the truth is: Plague never left.
Though we haven't seen a widespread epidemic of plague since the early 20th century, thanks to advances in sanitation and medicine, and there hasn't been a human-to-human case of transmission in America since 1924, an average of seven new cases are reported every year in the U.S. From 2010 to 2015, there were 3248 cases, including 584 deaths, reported worldwide, according to the World Health Organization.
Yersinia pestis, the flea-borne bacteria that's most often responsible for plague, infects rodents; humans are “incidental hosts,” who can acquire the infection if bitten by an infected flea or rodent. Compared to the 14th century, when the Black Death spread wildly, or the late 19th century, when 10 million people died of the disease after it traveled from Hong Kong to port cities worldwide, most people today live in more sanitary conditions and have less frequent contact with the rodents most likely to carry the infected fleas. Today, 95 percent of plague cases originate in parts of sub-Saharan Africa and Madagascar.
The most common of the three strains of plague is the notorious bubonic plague, which causes painful swollen lymph nodes (also called buboes) and was responsible for Europe's Black Death—so named because internal hemorrhages caused by the infection make the skin appear black. But the pitbull that infected four Colorado residents carried the rarer respiratory strain of pneumonic plague, which is contagious when the infected person coughs up infected particulates. There is also septicemic plague, the most lethal form, which infects the blood, and most often occurs when plague virus has gone undetected and is allowed to spread.
In the U.S., you're generally only at risk of contracting plague in late spring to early fall if you've been in a rural or semi-rural area of the West, especially New Mexico, Arizona, or Colorado, and have had contact with fleas or rodents including ground squirrels, chipmunks, prairie dogs, or rats. And even then, the risk is low.
Only the pneumatic version of plague is contagious from human to human (though untreated bubonic plague can become pneumonic), but you have to be coughed upon, or receive fluid from an infected person upon an open wound or directly into your mouth or nose.
Plague symptoms mimic any flu—fever, chills, headache, difficulty breathing or coughing—but people have been known to cough up blood with the pneumonic variety. If you've been in a rural area, or camping, and come down with these symptoms two to three days later, it's best to go to a hospital.
Now for some good news: While untreated plague is quite deadly, people with plague who are treated with antibiotics within 24 hours of infection have strong recovery rates.
So while it's good to be aware and take precautions, the chances of another plague pandemic remain slim.
This story was originally published in 2015 and has been updated.