The primary culprit in the recent flare-up caused by tainted steroids, Exserohilum rostratum, is not an especially picky eater. Although the fungus prefers grasses, it will dine on many items—including human brains.
The nation's ongoing fungal meningitis outbreak has killed 30 and sickened 419 people so far, but the fungus responsible has never wrought such havoc before. The fungus, Exserohilum rostratum, is a plant-eating generalist equipped with a spore-launching mechanism ideal for going airborne, is not an especially picky eater and, although it prefers grasses, will dine on many items—including humans. But just how a pathogen typically associated with the great outdoors got into the three lots of injectable steroids prepared inside an admittedly filthy laboratory—and why only three lots—remains a puzzling mystery.
The errant fungus has been identified in lab samples from 52 of those affected and was similarly found growing in unopened vials of the steroid alleged to have caused the outbreak, according to the U.S. Centers for Disease Control and Prevention. A third recalled lot is still being tested. But E. rostratum is not a household name, even among mycologists. The fungus, which seems to prefer tropical and subtropical environments, has turned up on a wide variety of plant species, says Kurt Leonard, an emeritus professor in the Department of Plant Pathology at the University of Minnesota.
Most often the fungus shows up on grasses and other monocots—plants often distinguished by flower parts in threes and parallel leaf venation—such as pineapples, bananas and sugarcane, but it has also been found on non-monocots such as grapes and muskmelon. It's a fungus that is not, apparently, very picky about its food. "It's just a really common fungus in the environment that mostly lives on dead and dying plant tissue," Leonard says. There are many such others, and many of them can also occasionally infect animals or people.