As Child Contracts Plague at Yosemite, a Look at Where Plague Happens in America

California officials said on Thursday that a child camping in Yosemite National Park fell ill with plague and was sent to a hospital.

The child’s family, from Los Angeles County, camped at Yosemite’s Crane Flat Campground in mid-July and visited other places in the Stanislaus National Forest. No other family members have been sickened, and the child is said to be recovering.

This is the third case of plague in the American West this year; there have been two plague-related deaths in Colorado. One adult died earlier this week after contracting the plague from an unknown source. The Pueblo City-County Health Department has not revealed his or her identity but said the person may have developed the disease after coming into contact with fleas on a dead rodent or other animal. The department also noted that a dead prairie dog in the western part of the county tested positive for the disease.

In June, Colorado teenager Taylor Thomas Gaes died just days after coming down with flulike symptoms caused by the septicemic plague that he was thought to have contracted from a flea bite, the Denver Post reports.

Board-certified infectious disease specialist Amesh A. Adalja, MD, an assistant professor at the University of Pittsburgh Medical Center, tells Yahoo Health that the West’s plague cases could be linked to a plague outbreak that happened in San Francisco around 1900, which “seeded the American rodent populations.”

An estimation of the “plague line.” To the west of the line, outbreaks happen. To the east, where there are no prairie dog habitats, they usually don’t. The line corresponds to the 100th meridian longitudinally. (Graph: Yahoo Health)

The last urban plague epidemic in the United States occurred in Los Angeles from 1924 through 1925, according to the Centers for Disease Control and Prevention. The plague spread from urban rats to rural rodents and became entrenched in many areas of the western U.S.

“They have dispersed throughout the western U.S., and there is a rough ‘plague line’ where cases occur, based on rodent migration patterns,” Adalja says.

The concentration of plague cases in the U.S. West. The outbreak in Illinois was caused by a lab error. (Map: Centers for Disease Control and Prevention)

Plague now occurs as scattered cases in rural areas, and most human cases are in two regions: northern New Mexico, northern Arizona, and southern Colorado; and California, southern Oregon, and far western Nevada.

Those rodents may carry infected fleas, which can then bite — and infect — a human.

There are three common forms of the plague: bubonic (an infection of the lymph nodes), pneumonic (an infection of the lungs), and septicemic (an infection of the blood). Gaes died of septicemic plague, while an outbreak in Colorado last year was pneumonic.

(Image: Centers for Disease Control and Prevention)

All forms of the plague are caused by Yersinia pestis — the same bacterium that caused the Black Death, which wiped out an estimated 200 million people in the 14th century.

But didn’t this die out in the Middle Ages?

Nope, says David Hooper, MD, chief of the Infection Control Unit at Massachusetts General Hospital. The plague has been carried by rodents ever since and “hangs around in low amounts” among some of them, he tells Yahoo Health.

Colorado, New Mexico, and Arizona have occasionally seen cases of the plague caused by the bites of infected fleas. However, last year’s Colorado outbreak had some cases that were thought to have spread from a person who had been infected by his dog. “It doesn’t occur very often, but several cases of the plague are seen each year,” Hooper says.

(Map: Centers for Disease Control and Prevention)

Indeed, an average of seven cases of the plague occur in the U.S. every year, the CDC reports. They’re typically seasonal, with most cases occurring between late spring and early fall.

According to Hooper, symptoms can vary depending on the type of plague a person contracts. But a high fever is present in nearly all cases, as well as flulike symptoms. People with pneumonic plague may also develop a bloody cough, and those who contract bubonic plague usually experience painful, swollen lymph nodes.

(Graphic: Centers for Disease Control and Prevention)

While many symptoms of the plague are similar to those of the flu, Hooper says, the big indicator is exposure to an infected animal. If you have symptoms of the plague and have been exposed to rodents or fleas recently, call your doctor immediately.

The plague is serious. If left untreated, the death rate is 50 percent or higher, Hooper says.

But there are ways to treat plague if it’s caught early enough.

The FDA approved the drug Levaquin in 2012 to treat the plague, joining other antibacterial drugs, such as streptomycin, doxycycline, and tetracycline, that are approved for the treatment of the infection. A vaccine is also in the works, according to the CDC, but nothing is expected to be available to the public in the near future.

Should you be overly concerned about getting the plague? Probably not. “It’s pretty rare and is a very extremely low risk to the overall population,” says Hooper. “All things considered, there are many more common diseases you are much more likely to encounter than the plague.”