Scientists say parasitic worms in the guts of Vikings may have made their modern descendants more vulnerable to asthma, emphysema, and other lung issues. The researchers published their findings last month in the journal Scientific Reports.

While parasites in the ancient world are nothing new, the Vikings’ worms are a relatively new discovery. Last year, scientists examined 1000-year-old poop recovered from a Viking latrine and discovered three different species of intestinal worms.

"Having this extra dimension in our work is extremely exciting for archaeologists," professor and archaeologist Søren Michael Sindbæk told Science Nordic." It means that we can begin to answer questions we couldn't answer before."

He was right. The authors of the new paper say those parasites changed Vikings’ DNA, which changed the DNA of their descendants, predisposing them to lung conditions.

Parasite expert and senior author Richard Pleass and his colleagues were interested in the way antibodies called immunoglobulin E (IgE) are affected by the protein alpha-1-antitrypsin (A1AT).

The researchers collected plasma samples from people currently infected with the parasites, then scanned the plasma, looking for interactions between IgE and A1AT. They found that one specific variant of the A1AT-producing gene was especially helpful in fighting off any diseases the worms might cause. Vikings with this particular gene variant were more likely to live—and more likely to reproduce, passing the gene onto their kin.

Unfortunately, this particular gene variant has more than one effect. Today, people born with this variant are more likely to experience A1AT deficiency, which can predispose them to emphysema, asthma, and chronic obstructive pulmonary disease (COPD). The deficiency is most common in Scandinavians.

“It is only in the last century that modern medicine has allowed human populations to be treated for disease-causing worms,” Pleass said in a press statement. “Consequently, these deviant forms of A1AT, that once protected people from parasites, are now at liberty to cause emphysema and COPD."

A1AT deficiency is treatable, but first you have to find out if you have it. The Alpha-1 Foundation and the World Health Organization recommend genetic testing for anyone with COPD, bronchiectasis, or treatment-resistant asthma.