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Aug. 17, 2017 -- Plague -- an infectious disease that killed millions of people during the Middle Ages -- is a scary illness.

But even as public health officials recently identified fleas carrying the disease in two counties in Arizona, they stressed that it is rare in this country.

The fleas in Navajo and Coconino counties tested positive for Yersinia pestis, the bacteria that causes bubonic plague.

“It’s not an epidemic. It’s just something that happens in our region because we have prairie dogs and they are a common carrier of this flea,” says Adam Wolfe, communications manager for Navajo County.

“Finding infected fleas in Arizona is not at all unusual and is usually handled by simply notifying residents of the risk,” says Thomas Skinner, a spokesman for the CDC.

The CDC says plague was first seen in the U.S. in 1900. While it is a very serious illness, it is also rare. On average, seven to 10 human cases a year are reported in the U.S., generally in rural and semirural parts of Western states like Arizona, Colorado, and New Mexico.

New Mexico health officials reported in June that two people were hospitalized in Santa Fe County with the plague, bringing that state’s total to three cases this year. It has had eight other cases since 2015, including one death.

“I think it's important to remember plague is a scary disease and it did take a big toll on the human population with the ‘Black Death.’ But now in the 21st century, we have effective antibiotics and diagnostic tests, so plague doesn’t have the same sense of dread in 2017 as it did in the 1400s,” says Amesh Adalja, MD, a spokesman for the Infectious Diseases Society of America.

What Is the Plague?

Plague is a serious bacterial infection caused by the bacteria Yersinia pestis. It is transmitted mostly through the bite of a rodent flea or contact with an infected animal. In rare cases, you can get it through droplets coughed or sneezed into the air.

Are There Different Types of Plague?

Plague can take different forms, and there can be some overlap between them.

Bubonic is most common. The CDC says more than 80% of U.S. plague cases have been the bubonic form, which involves the buildup of bacteria in the lymph node closest to where the bacteria entered the body.

When Yersinia pestis bacteria get into the lungs, they cause pneumonic plague. Septicemic plague happens when the plague bacteria spread through your body.

How Common Is It?

Between 1900 and 2012, there were 1006 confirmed or probable human plague cases in the U.S. The World Health Organization says between 1,000 and 2,000 cases are reported worldwide every year, although the actual number of cases could be higher.

The disease has been found in people of all ages -- from infants to age 95, although the CDC says half of cases are in people between the ages of 12 and 45. And while it can happen any time of the year, in the U.S., it is most commonly seen in late spring and early fall.

What Are the Symptoms?

Symptoms generally appear 2 to 6 days after exposure. They vary depending on how someone was exposed and which type they got. The incubation period can be shorter -- more like 1 to 3 days -- if you are exposed through the air.

The most common sign of bubonic plague is one or more swollen and painful lymph nodes, called buboes, that develop quickly. Patients with this form also can have a sudden onset of fever, headache, chills, and weakness.

Symptoms of the other two forms of plague may be less obvious. Septicemic plague also brings chills and weakness, and can cause fever, abdominal pain, and shock. In this form, the skin on fingers, toes, and the nose can turn black and die because blood can’t get to those extremities.

In pneumonic plague, you can have fever, headache, and weakness, along with quickly developing pneumonia. This leads to shortness of breath, chest pain, cough, and sometimes bloody or watery mucus.

Adalja says that since the plague is in certain geographic areas, health care professionals in those parts of the U.S. have more knowledge about the disease and know it's important to ask people about things that can make having it more likely.

“But clearly you can miss it,” he adds. “If someone has bubonic plague, that has a characteristic swelling. But if someone has pneumonic plague, it can be difficult to distinguish from regular pneumonia.”

How Is It Treated?

Without antibiotic treatment, all forms of the plague can be serious and even deadly. But the disease is treatable and curable, especially when it's caught early.

Early antibiotics are really important for these types of infections,” Adalja says. “We know mortality with septic shock risk increases every hour there isn’t an effective antibiotic on board.”

Before antibiotics, from 1900 until 1941, the CDC says 66% of people infected with plague died. But overall mortality decreased to 11% between 1990 and 2010. Deaths are still possible, although they are less common with bubonic plague and more common with septicemic or pneumonic plague.

Gentamicin and fluoroquinolones -- antibiotics for bacterial infections -- are typical first-line treatments in the U.S. They are generally given for 10 to 14 days intravenously in the hospital.

How Can You Prevent It?

There is no plague vaccine. Avoiding  fleas and being cautious around sick or dead animals is important. Take precautions like wearing rubber gloves if you are cleaning or skinning a wild animal.

If you live in an area where fleas have tested positive for the plague, other tips to stay healthy include:

  • Avoid rodent burrows, and don’t handle sick or dead animals.
  • Keep dogs on a leash.
  • Tell the health department if you see a sudden die-off of prairie dogs and rodents, which can signal plague.
  • Don’t let pets run loose, since that could expose them to infected fleas on wild animals. This is especially true of cats, which are very susceptible to the disease.
  • De-flea pets regularly.
  • Use insect repellent in areas where plague has been identified.
  • Don’t camp next to rodent burrows or sleep directly on the ground.

Show Sources

Adam Wolfe, communications manager, Navajo County, AZ.

Amesh Adalja, MD, Johns Hopkins Center for Health Security, Baltimore.

Thomas Skinner, CDC spokesman.

Coconino County, AZ, website: “Fleas test positive for plague in additional location in Coconino County.”

Navajo County, AZ, Facebook page, Aug. 11, 2017.

New Mexico Department of Public Health: "Additional Cases of Human Plague in Santa Fe County."

CDC: “Plague,” “Frequently Asked Questions,” “Recommended antibiotic treatment for plague.”

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