The first symptoms that Paul Gaylord noticed were those of the flu. Two days before, he had been bitten by his cat, who had seemed visibly sick to him. Doctors prescribed antibiotics to treat cat scratch disease, a bacterial infection that can occur after scratches or bites from these animals.

But the medications had no effect. Gaylord's condition worsened, he was admitted to an intensive care unit and eventually fell into a coma. He didn't have the flu or cat scratch disease: he had caught the plague. A disease that we usually associate with the Middle Ages and not with a state in the United States like Oregon, where Gaylord lived.

The nonspecific symptoms and the fact that plague is a rare disease today represent a problem. Because the disease has not lost any of its lethal capacity. Gaylord narrowly survived and told his story in 2014 in the British newspaper The Guardian.

Three forms of plague: bubonic, septicemic and pneumonic

Plague is caused by the bacteria Yersinia pestis. It can enter the human body through different routes and multiply extremely quickly. The bacteria damages the tissues of various organs, causes bleeding and, without treatment, is fatal in almost 100 percent of cases.

The most common form is bubonic plague. In this case, fleas act as vectors. When they bite a rodent infected with Yersinia pestis, they can later transmit the bacteria by biting a person. The microorganism multiplies in the lymph nodes and causes painful inflammation of them.

If the pathogen reaches the bloodstream directly, for example through the bite of an infected mammal, septicemic plague, that is, a generalized infection of the blood, can develop.

In pneumonic plague, the pathogen reaches the lungs directly through small droplets or aerosols emitted by an infected animal or person. This is the only form of plague in which human-to-human transmission is likely.

The plague: pandemic in the Middle Ages, rare disease today

Up to 3,000 cases of plague are reported worldwide each year, according to the Robert Koch Institute. Currently, the most affected regions are the Democratic Republic of the Congo, Uganda and, above all, Madagascar, where the last major outbreak occurred in 2017. There are between 250 and 500 infections annually. However, sporadic cases also continue to appear in the western United States.

During the Middle Ages, on the other hand, the plague alone caused around 25 million deaths between 1347 and 1353. That outbreak gave rise to a pandemic that lasted for more than 500 years and killed around 60 percent of the European population.

But Yersinia pestis didn't start infecting humans only in the Middle Ages. Archaeologists have detected the bacteria in skeletons more than 5,500 years old. For this reason, researchers conclude in a recently published study that this pathogen has been lethal to humanity much earlier than previously believed.

Why is there no more plague in Europe?

As devastating as the plague was in the Middle Ages, since 1945 it has disappeared from Europe. That year the last cases were detected on the French island of Corsica.

According to Holger Scholz, molecular biologist and director of the National Reference Laboratory for Yersinia pestis at the Center for Biological Risks and Special Pathogens of the Robert Koch Institute (RKI), the main reason is that today in European homes people no longer live with rodents infected by Yersinia pestis.

Prompt diagnosis and timely treatment can make the difference between life and death.

Holger Scholz and his team at the RKI work closely with institutions in areas where plague remains endemic, including the Laboratoire d’Analyses Médicales Malagasy, under the Ministry of Health of Madagascar. One of the main objectives is to strengthen the laboratory infrastructure to improve the diagnosis of the disease.

And that is urgent, because diagnosis constitutes one of the greatest challenges. Scholz recalls the case of a young American who went for a run and went to the doctor with flu-like symptoms. They sent him home to rest. “He died because no one thought about the plague.”

And this, despite the fact that there are very effective antibiotics to treat the disease. However, in practically all outbreaks the same thing happens: “The first patients almost always die because the diagnosis is not made in time and treatment is not started quickly enough,” explains Scholz.