Human case of the plague appears in Colorado. What to know about symptoms, how it spreads.

A human case of the plague has appeared in Pueblo County, Colorado, according to preliminary test results. It is the first case in the state since a child from La Plata County died in 2021.

Southern Colorado is a hot spot for the plague in the U.S., as it mostly occurs sporadically in rural areas. But this isn't the first case in the U.S. to make headlines this year. A New Mexico resident died of plague after being hospitalized for the disease, the state's department of health confirmed in March.

"This tragic incident serves as a clear reminder of the threat posed by this ancient disease and emphasizes the need for heightened community awareness and proactive measures to prevent its spread," New Mexico public health veterinarian Erin Phipps said in a news release at the time. That case marked the first human case of plague in the state since 2021 and the first death since 2020, officials said. 

Another case was reported in February. Health officials in Deschutes County, Oregon, confirmed a rare case of human plague in a local resident, marking the first reported case in the state since 2015. Officials said the individual was likely infected by their pet cat, which showed symptoms of the disease.

In 2020, California reported its first case of plague in five years. Officials said at the time that the patient, a resident of the South Lake Tahoe area, was recovering at home. Two fatal cases were reported in Colorado in 2015.

While reports of the plague can be scary, and the disease can be serious, experts say there's little cause for concern for most people. Here's what to know:

What is the plague?

Plague is a disease caused by Yersinia pestis, a bacterium found in rodents and their fleas.

In the Middle Ages, the plague caused tens of millions of deaths across Europe in a series of outbreaks known as the Black Death. While the bacterial infection is still around today, it is far more rare in modern times and it can be treated.

There are three types of plague: septicemic, pneumonic and bubonic, which is the most common form, accounting for around 80% of cases in this country. (More on each type below.)

The Centers for Disease Control and Prevention says 496 cases of plague were documented in the U.S. between 1970 and 2020, with almost all occurring in the West or Southwest. More than half of the cases were reported in New Mexico, followed by smaller numbers in Colorado, Arizona, California and Oregon.

How is the plague transmitted to humans?

People typically get the plague after being bitten by an inflected flea or handling an infected animal, according to the CDC.

Many types of animals can be affected by plague, including:

• Squirrels
• Mice and rats
• Prairie dogs
• Chipmunks
• Voles
• Rabbits

"Wild carnivores can become infected by eating other infected animals," the CDC notes. 

Cats and dogs can also lead to human infections. Cats are particularly susceptible to getting sick, and have been linked to several cases of human plague in the U.S. via respiratory droplets in recent decades.

Health officials say symptoms of plague usually start to appear two to eight days after a person was exposed to an infected animal or flea.

In some cases, pneumonic plague can spread when an infected person coughs, causing infectious droplets to spread. This is the only type of plague that can be transmitted between people.

What are the symptoms of plague?

Symptoms depend on what type of plague someone is infected with. 

Bubonic plague: A key symptom is painful, swollen lymph nodes in the groin or armpits, called buboes. Other common symptoms include fever, weakness, coughing and chills. The majority of cases seen in the U.S. are this type.

Septicemic plague: Septicemic plague occurs when the bacteria gets into the bloodstream. Patients may develop fever, chills, extreme weakness, adnominal pain, shock and possibly internal bleeding. Skin and other tissues, especially on fingers, toes, and the nose may turn black and die. The CDC explains that an infection may start out as septicemic plague or it can develop if a case of bubonic plague goes untreated.

Pneumonic plague: Untreated bubonic or septicemic plague can develop in the pneumonic plague, which spreads to the lungs. These patients may develop fever, headache, weakness, pneumonia, shortness of breath, chest pain, cough and sometimes bloody or watery mucous. Pneumonia could cause respiratory failure and shock. This type of plague is considered the most serious form of the disease, with a high fatality rate. 

Is there a treatment for plague? 

Plague can be successfully treated with antibiotics, the CDC says, but the earlier the better to improve chances of a full recovery.

"To prevent a high risk of death in patients with pneumonic plague, antibiotics should be given as soon as possible, preferably within 24 hours of the first symptoms," the CDC says. 

The bubonic type has a case-fatality ratio of 30% to 60%, according to the World Health Organization. 

Pneumonic plague, when left untreated, is always fatal and death can occur within 18 to 24 hours.

"The key for clinicians is suspecting plague in the first place, obtaining the right specimens to make a diagnosis, and initiating treatment even before the diagnosis is made — as soon as you suspect it, you should start treating while the evaluation is ongoing," Dr. Erica S. Shenoy, chief of infection control at Mass General Brigham healthcare system, previously told CBS News.

How to prevent getting plague

How do you keep your pets from exposing you to the plague? To protect yourself, protect them.

"It's important to keep fleas off your pets because fleas can transmit not only the plague but also other infections," says Dr. Céline Gounder, a CBS News medical contributor and editor-at-large for public health at KFF Health News. 

You can do this by applying flea control products, the CDC recommends.

"Letting your pets roam freely, particularly in parts of the western U.S. where plague is endemic, also increases their and your risk of exposure," Gounder says, adding that it goes beyond just preventing fleas. "Cats can also get the plague by eating infected rodents and can transmit the plague to people through the air, too."

The CDC recommends not allowing dogs or cats that roam outdoors in affected areas to sleep in your bed. 

Other steps you can take to protect yourself and your family include: 

• Reducing rodent habitats around your home, workplace and other areas.
  
• Using insect repellent if you may be exposed to rodent fleas during activities like hiking or working outdoors.
• Wearing gloves whenever handling potentially infected animals.

Other diseases can also be transmitted in similar ways. Health officials in Alaska say an elderly man there died in January after contracting a virus known as Alaskapox, possibly from a scratch from a stray cat. It was the first confirmed death from Alaskapox, also known as AKPV, which is related to the smallpox, cowpox and mpox viruses.

-Sophie Lewis contributed to this report.