Endocardial Fibroelastosis (EFE) is a heart disorder of young children. It’s characterized by a thickening of the inmost lining of the heart chambers, usually occurring in children under 2. Back in the day, a few decades ago, it was halfway common, killing about 1 in 5000 kids.
Now it’s much rarer, almost gone. For a long time (as far back as 1918) people suspected that the mumps virus had something to do with EFE. When an effective mumps vaccine was introduced in 1978, EFE practically disappeared. Since then, genetic investigations of preserved samples have pretty much nailed mumps as the main cause of EFE.
I don’t miss it.