What is human plague?

There are three different types of human plague, which is caused by the bacterium Yersinia pestis that is carried by rodents and fleas.

The first and most common type of plague is bubonic plague, which was contracted by the Oregon resident. This form of plague happens when plague bacteria get into lymph nodes and can cause fever, headache, weakness, and painful, swollen lymph nodes known as "buboes." According to CDC, bubonic plague typically happens from the bite of an infected flea.

The second type of plague is septicemic plague, which occurs when the bacteria get into the bloodstream. This version of plague can occur initially or after bubonic plague goes untreated. Septicemic plague causes the same fever, chills, and weakness as bubonic plague, as well as abdominal pain, shock, and sometimes other symptoms, such as bleeding into the skin and blackened fingers, toes, or nose. According to CDC, septicemic plague typically arises from flea bites or from handling an infected animal.

The third form of plague is pneumonic plague. This form of the disease occurs when the bacteria get into the lungs and is the most serious form of plague. Alongside all the other symptoms that plague brings, pneumonic plague also causes pneumonia and is the only form of plague that can be spread from person to person by inhaling infectious droplets.

The plague is treatable. Typically, patients will have blood and other samples, like sputum or pus, taken from a bubo and if plague is identified, they'll be treated with antibiotics and potentially medically isolated. "Early diagnosis and early treatment can save lives," according to the World Health Organization (WHO).

CDC notes that "if plague patients are not given specific antibiotic therapy, all forms of plague can progress rapidly to death."

Currently, there is no commonly available vaccine for the plague, though Steve Atkinson, associate professor of molecular and cellular bacteriology at the University of Nottingham in Britain, says improved sanitation, better living conditions, and healthcare have helped temper the disease. "The disease itself is just the same as the one that swept through Europe during the Black Death outbreak."

How common is the plague?

According to CDC, there are an average of seven cases of human plague reported each year in the United States, and around 80% of them are the bubonic form of the disease. Between 1900 and 2012, there have been 1,006 confirmed or probable human plague cases in the United States.

The disease is common in some wild rodent populations in the western United States, and cats can become infected if they ingest an infected rodent or are bitten by the fleas associated with the rodents.

"Pets that hunt are one of the highest risk groups," said Erin Phipps, New Mexico's state public health veterinarian. "Cats are very susceptible to plague, and it can be fatal to them."

The individual infected with plague in Oregon is likely to have been infected by a pet cat, health officials said. Officials added the patient and all close contacts have been provided medicine, and people in the community are not believed to be at risk. The cat was also treated but didn't survive.

"Plague has killed millions of people and is often considered a disease of the past. But plague is far from being eradicated," said Sophie Jullien, a pediatrician who has worked with WHO to develop a manual for plague surveillance and prevention. "The main reasons are because the bacteria causing plague live and survive in the ground and in animal reservoirs. … They can survive under the ground for years."

"It's a popular misconception that it's an 'old' medieval disease," Atkinson said. "In reality it's still around and is endemic in rodent populations in many parts of the world including the USA, parts of South America, Africa, Asia."

Atkinson added that "one key hotspot is Madagascar," and noted the country had an extended epidemic in 2017 for three months starting in August with 2,417 confirmed cases and 209 deaths. "There are still cases every year throughout the world," he said. (Suliman, Washington Post, 2/13; Boone, Associated Press, 2/13; Anthes, New York Times, 2/14)

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