What Causes Plague, What Are the Symptoms? First California Case for 5 Years Recorded at Lake Tahoe

California has recorded its first case of plague in five years after a resident of South Lake Tahoe contracted the disease.

The unidentified individual is currently under the care of a medical professional and is recovering at home, according to El Dorado County health officials.

The county's Health and Human Services Agency said the individual may have contracted the disease after being bitten by an infected flea while walking their dog along the Truckee River Corridor north of Highway 50 or the Tahoe Keys area in South Lake Tahoe.

However, health officials are currently investigating the situation, which is the first case of plague in the state since 2015 when two individuals were infected in Yosemite National Park in 2015. Both of these infected individuals recovered following treatment. Before these, the last case in the state was recorded in 2006.

What causes plague and what are the symptoms?

Plague is a disease caused by infection with the bacteria Yersinia pestis, which can be found in wild rodents and the fleas that feed off them. Typically, the bacteria is transmitted to humans through the bite of infected fleas.

However, infection can also occur after direct contact with the tissue or bodily fluids of an infected animal—for example, when a hunter skins a rabbit.

Plague can take many clinical forms, but the main types are bubonic, pneumonic, and septicemic, according to the Centers for Disease Control and Prevention (CDC.)

The most common of these is bubonic plague, which can occur after a bite from an infected flea or contact with contaminated tissue/fluids. Symptoms usually appear between 2-6 days after being infected and include fever, headache, chills, weakness and swelling of the lymph nodes, known as buboes, according to the CDC.

If left untreated, bubonic plague has a mortality rate of around 30-50 percent. But prompt treatment with modern antibiotics is usually effective, as is the case for pneumonic and septicemic plague.

Just like bubonic plague, septicemic plague can occur as a result of either the bite of an infected flea or contact with infected animal tissue or fluids. It occurs when plague bacteria enter and multiply in the blood stream. Sometimes, septicemic plague is the first manifestation of the disease, but it can also develop from bubonic plague that is left untreated. Septicemic plague is almost always fatal if prompt treatment is not received.

A flea depicted in a digitally-colorized scanning electron microscopic (SEM) image, 2017. Smith Collection/Gado/Getty Images

Symptoms include fever, chills, extreme weakness, abdominal pain, shock, and bleeding into the skin and other organs. This form of plague can lead to skin and other tissues turning black and dying, particularly on the fingers, toes and the nose.

Pneumonic plague, the most serious form of the disease, occurs when plague bacteria infects the lungs. It is the only form that can be spread from person-to-person via infectious cough droplets, which can be breathed in by another individual. However, this type of transmission is rare and has not been documented in the United States since 1924, requiring direct and close contact with a pneumonic plague sufferer.

The symptoms of pneumonic plague, which can also develop from untreated bubonic or septicemic plague, include fever, headache, weakness, and a rapidly developing pneumonia characterized by shortness of breath, chest pain, cough, and, sometimes, bloody or watery mucous.

If left untreated, pneumonic plague invariably results in death, usually as a result of respiratory failure. Someone who develops this form of the disease after breathing in infected droplets may become ill within just 1-3 days.

While plague is rare today, between 1,000 and 2,000 people contract the disease every year, according to the World Health Organization, with Madagascar, Peru and the Democratic Republic of Congo being notable hotspots.

In the United States, an average of around seven human plague cases are recorded every year, mostly in rural and semi-rural areas in the west of the country. It is most common in southwestern states, such as New Mexico, Arizona, and Colorado.

"Plague is naturally present in many parts of California, including higher elevation areas of El Dorado County," said El Dorado County Public Health Officer, Dr. Nancy Williams in a statement. "It's important that individuals take precautions for themselves and their pets when outdoors, especially while walking, hiking and/or camping in areas where wild rodents are present. Human cases of plague are extremely rare but can be very serious."

El Dorado County Health and Human Services Agency provides several tips for preventing plague infections:

  • Do not feed squirrels, chipmunks or other wild rodents.
  • Never touch sick, injured or dead rodents.
  • Do not allow your pets to play with or pick up sick, injured or dead rodents.
  • Do not camp, sleep or rest near animal burrows or areas where dead rodents are observed.
  • Look for and heed posted warning signs.
  • Wear long pants tucked into boot tops and spray insect repellent containing DEET on socks and pant cuffs to reduce exposure to fleas.
  • Leave pets home if possible; otherwise keep pets on a leash. Do not allow pets to approach sick or dead rodents or explore rodent burrows.
  • Protect pets with flea control products.
  • Pet cats are highly susceptible to plague and can pose a direct threat to humans. Keep cats away from rodents. Consult a veterinarian if your cat becomes sick after being in contact with rodents.
  • If you get sick after being in an area where plague is known to occur, consult a physician and tell them you may have been exposed to plague.