First it was Japan. Then Europe. Now investors are scanning the world for the next outbreak of stagnant inflation and tumbling yields.

The malaise of "Japanification" burst into the mainstream this year, leaving in its wake a record amount of negative-yielding debt. Quantitative easing and a low-rate regime in Europe delivered banner returns on the region's bonds — at the expense of bank profits and retirement savings. Many say it recalls Japan's lost decade.

It's a scourge that threatens to spread further — perhaps even to the United States. The world's largest economy might only need a slide into a "plain-vanilla recession" to succumb to zero yields, says Jan Loeys, a senior adviser of long-term investment strategy at JPMorgan Chase & Co.