THE BASICS

Plague is a non-native, infectious disease caused by the bacterium Yernia pestiswhich is generally spread by fleas from infected rodents to other mammals, including humans. Plague is the cause of the “Black Death”, which caused millions of deaths in the Middle Ages. Plague was introduced to the United States in 1900 by rats arriving on steamships.

People: Most US human cases occur in the western United States, with an average of 7 cases reported each year. People can become ill when the plague bacteria are transmitted through the bite of an infected flea, through direct contact with contaminated fluid or tissue, or through inhalation of infectious droplets. Symptoms vary, depending on how the bacteria entered the body, and may include fever, headache, weakness, abdominal pain, swollen, painful lymph nodes near the site of the flea bite, rapidly developing pneumonia, and shock. Symptoms may develop 2-8 days after exposure. Infections can be fatal without early antibiotic treatment. Post-exposure prophylaxis is also indicated for persons with known exposure to plague. However, there is currently no human plague vaccine available in the United States.

Animal: Plague has had significant impacts on some wildlife populations, causing large extinctions or even local extinctions. Many parks in the western United States have been affected by plague. In parks in the west, rodents most often attack squirrels, chipmunks, wood rats and prairie dogs. When animals die of plague, their fleas look for new hosts, thereby spreading disease and increasing the risk to humans. By protecting wildlife from plague, we can help protect ourselves.

Environment: Yersinia pestis is easily destroyed by sunlight and drying. When the bacteria is released into the air, it can survive for up to an hour.

PREVENTION

• See animals in the wild from a safe distance. Never approach or touch wildlife.
• Keep pets on a leash and up-to-date on flea and tick prevention.
• Stay on track and avoid contact with rodent burrows.
• Reduce exposure to rodents by eliminating food sources and nesting sites around buildings, removing brush, rock piles, firewood, and food supplies around living areas, and excluding rodents from buildings (see the NPS Rodent Exclusion Manual in the Resources section below).
• Use insect repellent if you think you may be exposed to fleas during activities such as camping, hiking, or working outdoors. Products containing DEET can be applied to both skin and clothing, and products containing permethrin can be applied to clothing. Follow the instructions on the label.
• NPS employees,
  • During an outbreak of plague among wild animals,
    • Discuss the situation with IPM. Environmental treatment with insecticides to kill fleas can be effective in the immediate vicinity of an outbreak, but the effects are short-lived.
    • Consider wildlife vaccination. Vaccines have been used successfully in some wild animals and can provide long-term protection.
    • Consider closing certain parts of the park based on a risk assessment.
  • Always follow safe work practices (see the USGS Safe Work Practices for Working with Wildlife in Resources section below).

ANSWER

• If you become ill after a potential exposure, contact your doctor and tell them about your concern. Also, report all confirmed illnesses to NP’s Office of Public Health ([email protected]) as directed in the “Illness Reporting” guide below.
• Report concerns about sick or dead wildlife to the park resource manager and the Wildlife Health Branch at [email protected].

(Last updated 6/14/2023)