Health & Fitness

‘Black Death’ risk up in western U.S.

CDPH investigators performing flea treatment at the Crane Flat campground, Yosemite National Park. Investigators treated for fleas in the campground burrows during the week of Aug. 14.
CDPH investigators performing flea treatment at the Crane Flat campground, Yosemite National Park. Investigators treated for fleas in the campground burrows during the week of Aug. 14. California Department of Public Health

In the 1300s, it was called the Black Death – a ruthless flea-borne disease that ravaged millions in Europe in the Middle Ages, infecting its hosts with swollen, pus-filled lymph nodes (or buboes), fever, nausea, gangrene, rashes and bloody coughs.

Today, people still think contracting the infectious disease means doom, said Janet Foley, co-director for the Center of Vector-borne Diseases at UC Davis. But it is easily curable if caught early.

In the past two months, two people became infected with the bubonic plague after visiting Yosemite National Park, a boy from Los Angeles and an adult from Georgia. In response, the state park closed two campgrounds and posted warning signs at all campsites. Both people have been treated and recovered.

“It is serious. It’s a fatal disease. It’s been a major driver of historical events,” Foley said. “(But) these days it’s treatable with antibiotics. Most of the cases where people do die are due to it taking too long to make a diagnosis and get it treated early.”

These are the first cases of plague contraction at the park since the 1950s and the first in California since 2006. The state has seen only 42 cases and nine deaths since 1970.

“Years go by and nary a word (from the disease) and then there’s something like this year,” said ranger Don Lane of the U.S. Forest Service at Lake Tahoe Basin. “(History) shows it. Plague definitely is heartless.”

Danielle Buttke, an epidemiologist at Yosemite National Park, said there have been an unusual number of human and wildlife cases this summer throughout the western United States, where plague cases are most common. The region has seen an average of five human cases annually since 2000, but nine cases have appeared over this summer, not including the presumptive positive case of the visitor from Georgia, she said.

Plague definitely is heartless.

Don Lane, ranger for U.S. Forest Service

Plague is a seasonal disease that becomes more active during the summer, Foley said. That’s also when rodent populations increase because of their reproductive cycles.

It’s also possible that the drought has increased the chances of human infection because animals and people are in closer quarters in nature, drawn to places with water, Foley said.

The disease comes in three forms: bubonic, septicemic and pneumonic. It is caused by a bacterium, Yersinia pestis, which infects fleas and rodents and is primarily transferred to humans when they are bitten by infected fleas or have handled a dead infected animal.

“The bacterium is going to live in the flea and the flea is going to live off of whatever it can bite, whether it’s dogs or squirrels or people,” Lane said.

If you think you may have been infected, it’s important to see a doctor right away. If the infection is not caught soon enough, it can spread to other areas of the body and develop into septicemic or pneumonic plague or result in death. But if caught early, chances of survival are very good.

“Be aware anytime you go into a forest or outdoor setting and you feel sick afterward,” Foley said. “It’s important to let (your) doctor know you were there.”

Pneumonic plague, which occurs when the bacteria has invaded the lungs, is the most serious and can be transferred between people through infectious droplets in the breath. Cats are particularly susceptible, so it’s important for people in plague-prone areas to keep cats away from rodents or keep them indoors, Foley said. Dogs are not as susceptible, but can also contract plague if poking around infected rodent burrows or carcasses.

State officials urge people not to touch any dead rodents or animals they find while camping, visiting national parks or exploring rural or undeveloped areas in the mountains or foothills of the Midwest, which are plague-endemic areas. Instead, they should contact park officials or whatever agency manages the area.

Once infected rodents or people are found at a state park, officials dust burrows in the potentially infected area with insecticide that is harmful to the fleas but not to the rodents, Buttke said. The state parks are also checked every year by the California Department of Public Health for plague and other infectious diseases.

Ashiah Scharaga: 916-321-1673, @AshiahD


A bacterial infection caused by Yersinia pestis that takes on three forms: bubonic, septicemic and pneumonic. It is a flea-borne disease spread through contact with infected animals, dead or alive, and flea bites.


Very low if caught and treated early


Fever, nausea, headaches, weakness and swollen, tender lymph nodes or buboes.


A round of antibiotics.


  • Use insect repellant that contains DEET.
  • Wear long pants tucked into socks or boots.
  • Don’t walk or camp near rodent burrows.
  • Avoid contact with wild rodents: Do not feed or touch them, especially if they appear sick or dead.
  • Keep pets away from wild rodents, and don’t allow wild rodents into homes, trailers or outbuildings.
  • Contact the local ranger or agency that manages the area about any dead or sick rodents you may see.

More information: Centers for Disease Control and Prevention, California Department of Public Health