A man was diagnosed with bubonic plague in El Dorado County, California, after being bitten by a flea during a camping trip, U.S. health authorities announced on August 21, 2025. The infection, caused by the Yersinia pestis bacterium, is rare but potentially fatal, prompting the Centers for Disease Control and Prevention (CDC) to issue alerts for rural areas. The patient, whose identity was not disclosed, is recovering at home under medical supervision. This is the first case in the region since 2020, according to the county. The disease, historically linked to devastating pandemics, circulates in wild rodents in the western U.S., requiring heightened vigilance from campers and residents. The situation underscores the need for preventive measures against fleas and rodents to avoid new cases.
The case reignites concerns about the bacterium’s presence in natural environments. The CDC records an average of seven human plague cases annually in the U.S., with higher incidence in states like California, New Mexico, and Arizona. Transmission occurs mainly through infected flea bites or contact with sick animals. The swift response from health authorities, with antibiotic treatment, ensured the patient’s stabilization.
- Recommended preventive measures: Use DEET-based repellents, apply flea treatments to pets, and avoid contact with wild rodents.
- Risk areas: Rural regions in the western U.S., such as El Dorado, with high rodent populations.
- Importance of early diagnosis: Prompt antibiotic treatment reduces complications.
The history of plague in the U.S. shows that, while rare, the disease remains a threat in specific areas, requiring ongoing monitoring.
Origin and circulation of the bacterium
Yersinia pestis, the bacterium responsible for the plague, is a zoonotic pathogen that circulates among rodents and fleas in natural environments, particularly in mountainous areas like El Dorado County. The region, known for its wildlife, facilitates the bacterium’s persistence in squirrels, marmots, and other rodents. CDC data indicate that California is one of the states with the highest prevalence of the bacterium in wild rodents, alongside New Mexico and Colorado.
Transmission to humans occurs primarily through infected fleas, which carry the bacterium after feeding on sick animals. Direct contact with bodily fluids of infected rodents also poses a risk. The current case shows no signs of an outbreak, but it reinforces the need for vigilance in rural areas. In 2020, another case in the same region led to awareness campaigns focusing on prevention and monitoring.
The El Dorado patient was treated with antibiotics, such as doxycycline, which are highly effective when administered early. The rapid response from health authorities prevented complications, but the bacterium’s presence in nature demands ongoing attention.
- Main reservoirs: Squirrels, marmots, and wild rats.
- Affected regions: Western U.S., particularly rural areas.
- Essential prevention: Avoid camping near rodent colonies.
- Monitoring: Testing fleas and rodents helps map risk areas.
Symptoms and forms of the disease
The plague manifests in three main forms, each with distinct characteristics requiring immediate medical attention. The bubonic form, diagnosed in the El Dorado patient, is the most common and is marked by painful swelling of the lymph nodes, known as buboes.
The pneumonic form, rarer, affects the lungs and can be transmitted through respiratory droplets, making it highly contagious. The septicemic form occurs when the bacterium spreads through the bloodstream, potentially leading to septic shock and organ failure. Symptoms typically appear within two weeks of exposure and include high fever, chills, extreme weakness, and localized pain.
Early diagnosis is critical for successful treatment. Antibiotics like ciprofloxacin and doxycycline are effective, particularly for the bubonic form. The current patient showed mild symptoms and is recovering, but more severe cases require immediate hospitalization.
- Bubonic form: Swollen lymph nodes, fever, and pain.
- Pneumonic form: Respiratory difficulties and transmission risk.
- Septicemic form: Risk of septic shock and severe complications.
- Treatment: Early antibiotics ensure recovery.
Preventive actions in risk areas
Preventing the plague relies on simple but effective measures to avoid contact with fleas and rodents. Health authorities recommend using DEET-based repellents on exposed skin and regular flea treatments for pets.
Camping in areas away from rodent colonies or debris piles reduces the risk of flea bites. Keeping residential areas free of trash and dense vegetation is also crucial. The CDC advises that individuals with symptoms like fever or swollen lymph nodes seek medical care immediately, especially after outdoor activities.
Local campaigns in El Dorado have encouraged property cleanups and reporting of dead rodents, which may indicate the bacterium’s presence. These actions help map risk areas and prevent new cases.
- Repellents: DEET-based products are effective against fleas.
- Protected pets: Regular flea treatments prevent transmission.
- Property cleanup: Reduces rodent habitats.
- Vigilance: Reporting dead rodents aids monitoring.
History of the plague in the United States
The plague arrived in North America around 1900, likely through ships carrying infected rats. Since then, Yersinia pestis has established itself in wild rodent populations, particularly in western states like California, Arizona, and New Mexico. Between 1970 and 2020, the CDC recorded about 500 human cases, with an 11% mortality rate in untreated cases.
Most cases occur in rural areas, where contact with wildlife is more common. California, with its vast rural areas and rodent populations, is one of the most affected regions. The recent El Dorado case underscores the importance of epidemiological surveillance and access to antibiotics, which have significantly reduced risks.
The bacterium remains endemic in wild rodents, such as squirrels and marmots, making prevention the primary tool against the disease. Public education and ongoing monitoring are essential to avoid new cases.
- Plague introduction: Arrived in the U.S. around 1900 via infected rats.
- Incidence: About 500 cases recorded between 1970 and 2020.
- Mortality: 11% in untreated cases.
- Prevention: Education and surveillance reduce risks.
Response from health authorities
El Dorado County authorities, in partnership with the CDC, are intensifying efforts to monitor the situation. Public health teams are inspecting camping areas and trails to identify rodent infection hotspots. Informational leaflets are being distributed in parks and campgrounds, providing prevention guidance.
The use of rodent traps and laboratory testing of fleas has helped map the bacterium’s presence. These actions enable rapid interventions in high-risk areas, reducing the likelihood of new cases. The response to the current case was effective, but ongoing vigilance is necessary to prevent outbreaks.
- Monitoring: Traps and tests identify risk hotspots.
- Campaigns: Informational leaflets guide the public.
- Collaboration: Partnership with the CDC ensures coordinated actions.
- Ongoing prevention: Surveillance reduces outbreak risks.