How Medieval Plague Still Shapes Your Health

Plague is probably not on your radar as a disease to worry about, but it serves as a powerful reminder of history’s lasting impact.

About 700 years ago, this bacterial disease — once called the Black Death — claimed the lives of around 200 million people. That was roughly half of Europe’s population at the time.

A study recently published in the journal Nature examined DNA from skeletons dating back to the 1300s. Scientists found a genetic variant that appeared to help some people survive the plague. Those with this variant had a 40% higher chance of survival. It turns out, you might carry the gene that protected your relatives from plague, but now, its effect on you could be very different.

Those individuals who survived the plague reproduced and passed the beneficial gene to their children. Of course, those without the gene died and couldn’t pass it on. This is evolution in action.

Today, plague is rare, but it has certainly not disappeared. It’s present in the Western US, Asia, and Africa. Earlier this month, the Arizona Department of Health Services confirmed that a patient died from Yersinia pestis — the bacterium that causes plague. In June, another case was reported in Oregon. The last urban outbreak of rat-associated plague in the United States happened in Los Angeles 100 years ago.

Plague affects both animals and humans. Most humans get sick after being bitten by a flea from an infected rodent. The disease can also spread through direct contact with infected tissue or fluids — like when hunters handle an infected animal.

The two most common forms of plague are bubonic and pneumonic. People with bubonic plague experience fevers, chills, weakness, and painful, swollen lymph nodes called bubos. Pneumonic plague affects the lungs. It causes shortness of breath, chest pain, and cough. This form can spread from person to person and has a very short period from infection to symptom onset — often as little as one day.

The good news? Plague can be treated with antibiotics. But a quick diagnosis is crucial. If you live in areas where plague is present, avoid contact with sick or dead animals and use insect repellent to prevent flea bites.

Now, here’s that evolutionary twist. The same gene that protects against plague is now linked to autoimmune diseases in people today — causing conditions like Crohn’s disease, where our immune system attacks the body’s own tissues.

The thinking is that the plague bacteria shares similarities with some human proteins. In some people, when there’s no infection, the antibodies mistake our own tissue for plague and cause an autoimmune reaction.

It’s a striking example of how our bodies carry the imprint of ancient struggles. What saved our ancestors 700 years ago is now making some of us sick today. The Black Death isn’t just history — it’s written in our DNA, still shaping human health centuries later.

– Dr. Michael Wilkes with a Second Opinion