Plague in National Parks: Risks and Prevention

Part of the National Park Service's A–Z health topics for employees, volunteers, commercial operators and visitors.

Reported cases of human plague in the United States, 1970–2020. CDC.

The basics

Plague is an infectious disease caused by the bacterium Yersinia pestis, usually spread by fleas from infected rodents to other mammals, including people. It is not native to North America: it caused the "Black Death," which killed millions in the Middle Ages, and arrived in the United States in 1900 with rats on steamships.

In people

• Most U.S. cases occur in the western United States — an average of 7 a year.
• People are infected by the bite of an infected flea, by direct contact with contaminated fluid or tissue, or by breathing infectious droplets.
• Symptoms depend on how the bacteria entered the body and can include fever, headache, weakness, abdominal pain, swollen, painful lymph nodes near a flea bite, rapidly developing pneumonia and shock. They appear 2–8 days after exposure.
• Plague can be fatal without early antibiotics. People with known exposure should get preventive treatment. There is no human plague vaccine available in the United States.

In animals

Plague has caused large die-offs and even local extinctions of some wildlife, and many western parks have been affected. The rodents most often hit are squirrels, chipmunks, woodrats and prairie dogs. When animals die of plague, their fleas seek new hosts, spreading the disease and raising the risk to people — so protecting wildlife also protects us.

In the environment

Y. pestis is quickly killed by sunlight and drying; released into the air, it can survive for up to an hour.

Prevention

For everyone

• Watch wildlife from a distance — never approach or touch it.
• Keep pets leashed and up to date on flea and tick prevention.
• Stay on trails and away from rodent burrows.
• Around buildings, remove food and nesting places — brush, rock piles, firewood, food supplies — and keep rodents out of buildings.
• Use insect repellent if you may be exposed to fleas while camping, hiking or working outdoors: DEET on skin or clothing, permethrin on clothing, following the label.
• Follow safe work practices when working with wildlife.

For parks during a wildlife outbreak

• Talk with the park's integrated pest management staff: insecticide treatment can kill fleas near an outbreak, but the effect is short-lived.
• Consider vaccinating wildlife, which has worked for some species and can give long-term protection.
• Consider closing parts of the park based on a risk assessment.

If you get sick

• If you fall ill after a possible exposure, see a health care provider and tell them your concern. Park Service staff should report confirmed illnesses to the NPS Office of Public Health.
• Report sick or dead wildlife to the park's resource manager and the NPS Wildlife Health Branch.

Sources

Based on "Plague," National Park Service health topics series; a work of the United States government in the public domain.