Last update: September 8, 2015
Jump to campground closures or general plague information sections
Plague Situation in Yosemite
What is happening with plague in Yosemite?
In recent weeks, a minor was diagnosed with plague after camping in Crane Flat Campground and visiting the Stanislaus National Forest and other areas outside of Yosemite. As a result of the environmental investigation that followed, a squirrel captured at Crane Flat tested positive for plague. On the recommendation of the California Department of Public Health (CDPH), the Crane Flat Campground was closed for several days to allow park and CDPH staff to treat rodent burrows with the insecticide deltamethrin to kill fleas. Fleas on rodents, especially squirrels and chipmunks, can carry the bacterium that causes plague. Crane Flat Campground re-opened after the treatment on Friday, August 14.
The Tuolumne Meadows Campground closed during the week of Monday, August 17 to allow for similar treatment. This precautionary measure was taken after two dead squirrels collected at the campground tested positive for plague.
A second traveler who visited the park was diagnosed with a possible case of plague later in August. The individual did not camp in Yosemite, but hiked in the park, Sierra National Forest, and other surrounding areas. An environmental investigation of the sites the person visited was conducted.
Additional investigations by CDPH led to the recommendations to treat Tamarack Flat Campground and the Glacier Point area with deltamethrin to reduce the flea populations and the risk of human exposure to plague. Treatment was done on August 30 at Tamarack and August 31 at Glacier Point. Both sites are once again open to the public.
If plague is such a rare disease, why are there two cases with links to Yosemite? There were also some cases in Colorado. Why so many this year?
Health officials are seeing increased plague activity throughout much of the western United States so far in 2015. Since April 1, 2015, 11 human cases have been reported nationwide, compared to an average of five per year since 2000. Officials do not know exactly why there are more cases this year or why they are seeing plague activity in so many different areas this year. Human cases are still rare in the United States.
Why were Crane Flat and Tuolumne Meadows campgrounds closed?
Out of an abundance of caution, Yosemite National Park staff worked with state and federal public health officials to treat rodent burrows in the campgrounds to kill fleas in order to reduce the risk of plague in both humans and wildlife. Campgrounds were closed for short time to minimize human contact with deltamethrin.
Plague is widespread in rodent populations in much of California and the park already does routine surveillance to check for it. So why did the park treat the campgrounds now?
In early July, a visitor who stayed in Crane Flat Campground and traveled to other surrounding areas, including Rainbow Pool in the Stanislaus National Forest, was diagnosed with plague. During the environmental investigation that followed, a rodent collected from Crane Flat tested positive for plague, which lead to the decision to dust the campground with the insecticide deltamethrin (brand name Delta Dust). Later, a number of dead squirrels found at the Tuolumne Meadows Campground also tested positive for plague. So although there have been no new cases of plague in people linked to the campground, the park and public health officials decided to treat the Tuolumne Meadows Campground, too.
Subsequent investigations lead the CDPH to recommend the park also treat fleas at Tamarack Flat Campground and Glacier Point. The treatment was done August 30 and 31.
If I am staying in Crane Flat or Tuolumne Meadows campgrounds, what should I do to prevent contact with deltamethrin?
Please avoid contact with rodent burrows to protect yourself from plague and to minimize contact with deltamethrin. Also, be sure to keep pets on a leash at all times and supervise your children to make sure they do not go near rodent burrows or touch dead animals. If you find a dead animal, report it to a park ranger.
What is deltamethrin?
Deltamethrin is a commonly used insecticide that comes in the form of a white powder. It is from a class of pesticides called pyrethroids. Pyrethroids are the most often used household insecticide. They are used on pets to control fleas and ticks as well as on clothing and lawns to kill mosquitoes and ticks—they are even found in shampoo to kill lice. Deltamethrin is used in agriculture on many crops that we eat including apples, corn, vegetables, and coffee. Pyrethroids were originally isolated from the chrysanthemum flower, which have been used to kill ticks and mosquitoes in Asia since the 1800s.
What happens to deltamethrin in the environment?
Deltamethrin binds to the soil and is broken down quickly. It typically breaks down within 1-2 weeks. It does not become airborne or volatilize. It dissolves in water quickly and can be toxic to aquatic organisms and amphibians, so should not be used near creeks, streams, or surface water. Deltamethrin is also toxic to honeybees and dragonflies.
How might I be exposed to deltamethrin?
You can be exposed to deltamethrin if you touch, eat, or breathe it in. Do not disturb any rodent burrows to avoid stirring up soil that may have had deltamethrin applied.
General Plague Questions
What is plague?
Plague is a disease caused by a bacterium, Yersinia pestis, that can be transmitted to humans via rodents and their fleas. Plague in Yosemite is most commonly associated with fleas found on ground squirrels and chipmunks. Plague in humans is very rare, with only about 5 cases per year in the United States.
How do I get it?
Plague is commonly transmitted through the bite of an infected flea or from handling sick or dead animals infected with the bacteria. Although rare, it can also be caught through contact with infectious respiratory droplets, from coughing or sneezing. While squirrels and chipmunks are the most common sources, any animal, including domestic pets like dogs and cats, can transmit the disease through their fleas or, if infected with pneumonic plague, through coughing or sneezing.
What are common symptoms of plague?
There are three main forms of plague: bubonic, septicemic, and pneumonic. Generally, the initial symptoms of plague develop two to six days after exposure and include nausea, vomiting, fever, chills, muscle aches, headache, and weakness. Bubonic plague, the most common form, is characterized by swollen and tender lymph nodes (called "buboes") in the groin, neck, or armpit. In septicemic plague, plague bacteria infect the bloodstream, causing high fever, fatigue, weakness, and bleeding disorders. Pneumonic plague is an infection of the lungs that can follow bubonic or septicemic plague, or occur directly from inhalation of plague bacteria. Patients with pneumonic plague have difficulty breathing, develop a cough, and may spit up blood-tinged saliva.
Where can I get more information?
More information is available from CDC, CDPH, and from the National Park Service
How have visitors been advised of plague risks and symptoms?
Messaging is posted throughout the park telling visitors not to feed or approach wildlife and visitors are encouraged to wear insect repellent. These actions will protect against a variety of risks, including plague. The CDPH issued news releases on August 6, August 14, and August 18, 2015 that described the situation. Relevant information is also available on the park's website. Additionally, the park participated in outreach to physicians about plague on August 28. Park rangers routinely educate visitors on the importance of avoiding contact with wild animals. Plague fact sheets are available at visitor centers and entrance gates. Information on how to limit the risk of exposure to plague—in addition to the other risks inherent in wild places like Yosemite—is available on the park's website.
How can I reduce my risk of exposure to plague?
Public health officials recommend the following:
Do not feed wildlife.
Use insect repellents (20-30% DEET or equivalent) when outdoors. Wear closed-toed shoes and tuck pants into socks when possible.
Avoid touching live or dead rodents or disturbing rodent burrows, dens, or nests.
Do not pitch tents or place sleeping bags in proximity to rodent feces or burrows or near possible rodent habitat (for example, dense brush or woodpiles).
Keep food in tightly sealed containers (including those stored in food lockers) and store away from rodents.
Contact a park ranger if signs of rodents are present, including feces or urine.
Dispose of all trash and garbage promptly in accordance with campsite regulations by discarding in rodent-proof trash containers or packing it out in rodent-proof containers.
Keep wild rodents out of homes, trailers, and outbuildings and away from pets.
Supervise children and keep pets on a leash at all times.
What is the park doing besides treating some campgrounds?
Federal and state public health officers regularly conduct rodent surveys to monitor rodent abundance and the presence of the bacteria in rodent populations. The park conducts routine plague surveillance with CDPH as part of normal park operations. The park is continuing its rodent-proofing and trapping measures throughout the park. Hundreds of bear-resistant food storage lockers have been retrofitted to ensure mice cannot get in through drain holes or other tiny entry points.
Is it safe to visit Yosemite?
Based on information received from public health organizations, the risk remains low. Plague is a rare disease but is endemic throughout the Sierra Nevada mountains and foothills as well as other parts of California; however, visitors to areas where there are rodents such as squirrels and chipmunks should take precautions to avoid exposure and to be aware of the risks and symptoms associated with the disease.
The park is open and we continue to welcome visitors.The park is a natural environment that contains wild animals, swift water, and other inherent risks, including exposure to animal-borne diseases like plague. The National Park Service and its partners have extensive safety protocols in place to mitigate those risks to the greatest extent possible. All visitors should be aware of safety information related to visiting Yosemite.
What is the NPS doing at other parks to reduce the risk of plague infection?
NPS conducts surveillance in wildlife for plague throughout the western United States and works closely with state and local health departments whenever plague is detected in the environment. The NPS is also working with several states and the USGS National Wildlife Health Center to develop and test an oral plague vaccine in several NPS park units to reduce wildlife and human health risk of plague.