Your Body

How do we still have the plague, centuries after the Black Death?

Story highlights

The bacterium that caused the Black Death is associated with a handful of plague cases in the U.S. every year

People get infected through a bite from a flea that was living on an infected rodent, cat or dog

Flu-like symptoms can make it hard for people to realize they need medical attention

CNN  — 

The word “plague” brings to mind the great scourge of the Middle Ages that filled the streets and so-called plague pits with the bodies of its victims.

But as recent news reports remind us, we cannot entirely dispatch the plague to the annals of history. Yersinia pestis, the same type of bacterium that was responsible for the pandemic that wiped out 60% of the European population between the 14th and 17th centuries, maintains a foothold in the United States and around the globe in rodents and the fleas that live on them.

Thankfully, however, today infections are treatable with antibiotics if they are caught early enough. “The tragedy in most cases is that people don’t realize what they have and think they have the flu,” said Sharon Collinge, professor of environmental studies at University of Colorado-Boulder.

The most recent case to make headlines is that of Taylor Gaes, who died of the plague at the beginning of June, a day before he would have turned 16. Officials think that Gaes was infected through a flea bite on his family’s ranch in Larimer County, Colorado.

A map shows reported cases of human plague in the United States from 1970 to 2012.

Since 1970, there have been anywhere from a few to a few dozen cases of plague every year in the United States, most of them occurring in Western states, according to the Centers for Disease Control and Prevention. Globally, Africa, South America and Asia have the most plague cases, particularly Madagascar, Peru and India. Hardest hit of all is the Democratic Republic of Congo, which had more than 10,000 cases from 2000 to 2009.

“It’s like a lot of pathogens, it’s persistent and emerges at certain times and places for reasons that still remain somewhat mysterious,” Collinge said. “It would be hard to get rid of all those fleas in the environment and completely eradicate it,” she added.

Related: Is your pet going to make you ill?

The bacterium infects a range of rodents, including rats, prairie dogs and ground squirrels, as well as pets such as cats and dogs. It is transmitted to people though bites from fleas that were living on infected animals, or in rare cases, directly from infected rodents or pets to people. Although rats have long been considered the culprit for the largest plague epidemic in history, the Black Death of the Middle Ages, a recent study suggested that gerbils and their fleas, hitching a ride on trade routes from China, were actually the main vector of disease.

For reasons that are unknown, some people probably recover from the infection without antibiotics. “It’s such an uncommon disease, I don’t know if it’s been studied well enough to know if certain people have increased susceptibility,” such as older people or people with chronic diseases, said Dr. Michelle A . Barron, associate professor of infectious diseases at University of Colorado Medical School.

In cases where the disease progresses, it can develop into three different forms. The form that is synonymous with plague itself, bubonic plague, is associated with swollen and black-and-blue lymph nodes (the origin of “Black” Death), usually near the site of the flea bite. Bubonic is seen in about 80% of cases in the U.S., according to the CDC. The other two forms infect the blood (septicemic) and lungs (pneumonic).

Although septicemic and pneumonic plague are inevitably fatal if untreated, Barron said that most patients with these forms can still make a full recovery with antibiotics. Supportive care also plays a big part in recovery and can include fluids for dehydration and oxygen in cases of pneumonic plague, she added.

Unless a patient has the telltale swollen lymph nodes of bubonic plague, it can be hard for the person to know he or she has the plague. Symptoms are generally similar to those of the flu: fever, chills, headache, weakness. “A lot of it is history, (whether) you live on a farm or ranch or are outdoorsy,” Barron said. “I tell my patients all the time, ‘Please canvass your mind. If you just came back from Madagascar, please tell me,’” she added.

Why plague is more common in areas like the western U.S. is among the mysteries that surround the ancient scourge. The heat and aridity of these environments, as well as the burrows dug by rodents such as prairie dogs and ground squirrels that live out West, probably create a particularly hospitable habitat in which fleas flourish, said Collinge.

Even though the bacterium responsible for plague still lurks in the environment, it leads to much less death and disease than in past decades and centuries. The most recent plague epidemic in the U.S., in Los Angeles from 1924 to 1925, claimed about a dozen lives.

Basic hygiene probably deserves the credit for the low number of plague cases, Barron said. “I think most of us would not tolerate having rodents in our homes, and back when the plague occurred in Europe, living conditions were just not that good,” she said.