A new plague case is a reminder: The 'Black Death' lingers in the US

Plague is no longer the human scourge it was during “The Black Death,” when it wiped out entire generations of medieval Europe and Asia.

Nor does it pose the same threat it did when dense, unsanitary port cities along the West Coast allowed the plague to fester in the early 1900s.

But still, plague infec ts a handful o f Americans every year and when Colorado officials confirmed this week that a person in Pueblo County had been sickened , they sprang into action with warnings.

They cautioned against exposure to rodents, such as prairie dogs, known to carry fleas with the Yersinia pestis bacterium that causes plague. They also told people to be careful about pets hunting or roaming near where rodents live. And encouraged them to get their pets treated for fleas and not to share a bed with pets.

Times have changed and antibiotics can now treat the plague, but it remains a serious disease, experts said.

“Living conditions were very different than they are now,” Rebecca Eisen, a research biologist for the Centers for Disease Control and Prevention in Colorado, told USA TODAY. “We had high-density urban environments that were often rat-infested. That was a great breeding ground for transmission of plague.”

However, a century after the last urban plague outbreak in the U.S., the disease remains a perennial and serious risk in parts of the western U.S. for populations that live near infected rodents. Outbreaks, though contained or rare, become the subject of widespread media coverage when cases pop up.

Plague terrorized the globe, killed millions of people

The first recorded cases of bubonic plague killed millions of people across the Mediterranean region. They began in the 6th century and endured until the 8th century.

In the 14th century, the Black Death broke out along the Silk Road, the trade route between modern China and Europe, killing about 50 million people in Europe, more than a quarter of the population, according to the Science Museum in London. Some estimates put it higher.

Outbreaks came again in the late 1500s and continued through the 1700s. Historians estimate 2.5 million people died of the disease in France alone between 1600 and 1670.

Another pandemic began in the mid-1800s in Yunnan, in southwestern China. Several Asian port cities , such as Hong Kong and Bombay (now Mumbai), had outbreaks of bubonic plague in the late 19th century. More than 10 million people died of the disease in India in that era.

After 1900, rats and stowaways aboard ships from countries with outbreaks brought plague to American ports, including Honolulu and San Francisco. Public health officials in the western U.S. scapegoated people in the Chinese and Mexican communities, wrongfully blaming them for being carriers of disease.

Honolulu officials began burning homes in the city's Chinatown, resulting in a fire that destroyed nearly all of the neighborhood.

San Francisco officials attempted to quarantine all of its Chinatown, forcing Chinese people to live in crowded unsanitary conditions in a densely packed area. Officials believed Chinese people carried the disease, but allowed white people to leave the quarantined area.

Los Angeles experienced the country's largest and last urban outbreak of plague in the mid-1920s, which was traced to a dead rat under a home in the city’s “Little Mexico” neighborhood just east of downtown. In response to 30 deaths, the city health department quarantined the area. Thousands of buildings in the neighborhood were destroyed.

Plague never went away, still circulating out West

Plague, which comes in several different forms, has not had the same reach in the past century, though it’s considered endemic in parts of Africa and South America, according to the World Health Organization . In the U.S., the disease was first carried by fleas on rats in West Coast cities. It retreated into the interior western U.S., and fleas carrying the bacteria found plentiful reservoirs in rodent populations such as squirrels and prairie dogs in rural and semi-rural areas.

Plague is now mostly found in semi-arid upland forests and grasslands, according to the CDC.

“This wasn't an endemic disease that was already established,” Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security. “This was something that basically came to the United States in the early 1900s, and is very geographically restricted.”

People don’t have the same exposure to fleas as they did in the 1900s, he added.

Most U.S. cases occur in the Southwest and the West . About seven people get plague every year, according to CDC data. Between 1970 and 2022, there have been 500 plague cases in the U.S.

Three people have contracted the plague so far this year, according to the CDC. A New Mexico man died from bubonic plague in March. In February, an Oregon person contracted plague . Officials say the disease was likely transmitted by the person’s infected cat. The Colorado case this month is the third.

Bubonic plague, thankfully, does not spread person-to-person

Symptoms of plague develop within one to seven days after exposure, according to the WHO . It typically causes sudden fever and chills, severe headache, muscle aches, nausea and vomiting.

A common symptom is swollen, painful lymph nodes, called buboes. Buboes give bubonic plague, plague’s most common form of disease, its name. These manifest in the body as swelling in the armpits, groin and neck, according to the Mayo Clinic .

Bubonic plague, along with septicemic plague do not pass from person to person. Direct contact with fleas is required, according to the CDC said.

A third type, pneumonic plague, which caused the 1924 Los Angeles outbreak, occurs when bubonic or septicemic plague is left untreated and spreads to the lungs. It can also occur when Y. pestis infects the lungs. In that case, it can spread from person to person when someone inhales the bacteria breathed out by the infected person.

Antibiotics administered early can easily treat plague. Vaccines have been developed, however, they are not available in the U.S.

Take plague seriously, but don’t worry too much

Thanks to public health and sanitation, plague is no longer the threat it was in past centuries.

However, Colorado health officials took precautions all the same, warning residents to destroy areas where rodents can hide and breed near their homes. Officials also told people to be careful about pets hunting or roaming near where rodents live. Pets must get regular treatment for fleas, officials said. They warned people not to let pets sleep with them.

“Humans are really accidental hosts,” said Dr. Michelle Barron, senior medical director for the UCHealth Infection Prevention and Control and a professor of medicine and adviser to the Colorado School of Public Health. “It's when you come into contact with the animals, or the fleas that are associated with the animals, that they then end up infected.”

This article originally appeared on USA TODAY: A new plague case is a reminder: The 'Black Death' lingers in the US