LONDON (StudyFinds) — Mononucleosis, which many simply refer to as “mono” or the “kissing disease,” may be the reason some people develop multiple sclerosis later in life. A team in Sweden finds this common infection among children and teens significantly increases the risk of developing MS as an adult.

Doctors have been diagnosing cases of MS since the 19th century. The autoimmune disease tends to develop slowly, eating away at the protective covering around a patient’s nerves — the myelin sheath. This causes many — sometimes debilitating — symptoms including pain, fatigue and a decline in motor function.

Previous research has examined whether genes which put someone at higher risk for multiple sclerosis make them more susceptible to other severe infections. The new study, however, looked at the connection between infections and the eventual development of multiple sclerosis.

“Some scientists have suggested that infections like glandular fever (also called infectious mononucleosis “mono” or “kissing disease”) might be worse in people who will go on to develop MS because their immune system is already different,” writes study author Scott Montgomery from University College London in an article in The Conversation. “But another explanation – the one that our study investigated – is that the infection triggers MS.”

Mono is an infection transmitted through saliva and is a common ailment among children going through puberty. Symptoms often include severe fatigue, fever, a rash or swollen glands. One of the main treatments for mono is rest.

Teens are at greatest risk

Researchers looked at the impact of glandular fever at different ages among 2.5 million people in Sweden. The team also took into account the health of the participants’ siblings, which could confirm or discount the role of familial genetics in MS development. In total, doctors diagnosed around 6,000 participants with MS after the age of 20.

Results show children contracting mono between the ages of 11 and 19 have a significantly higher risk of developing MS as an adult. Specifically, this risk was highest among children with mono between 11 and 15 — the typical window for puberty. Children with glandular fever before the age of 11 had a lower risk of eventually having MS. Researchers also discovered that the risk of developing MS continues to drop the older a person contracting mono gets — with the risk all but disappearing by age 25.

“Changes in the brain and immune system as people age may help explain this,” Montgomery writes.

So how does mono trigger future disease?

Study authors say these infections during childhood may get into the brain, where MS does its damage as well. Although the most at risk for multiple sclerosis are between 11 and 15 years old, researchers say many won’t receive an MS diagnosis until they reach their 30s.

Once that deterioration begins, it can become progressively worse as time goes on. Modern medicine continues to work on finding a cure for the disease and some treatments can slow its progress.

“This study provides stronger evidence that a severe bout of glandular fever (and likely other serious infections) during the teenage years – particularly around puberty – can trigger MS, even though, often, MS may not be diagnosed for at least 10 years after the infection,” Montgomery concludes.

The team published their findings in JAMA Network Open.