Fishermen have found strange lesions on fish

From Medical Correspondent Elizabeth Cohen

(CNN) -- First, fishermen in Maryland started noticing strange lesions on fish in the Chesapeake Bay. Then, about a year ago, some of them began to experience strange symptoms of their own.

"I just forget stuff," said fisherman Tommy West. "If I'm working on something, I'll have to stop sometimes right in the middle of what I'm doing and put my thoughts together."

A newly published study shows that these men weren't imagining things. Brain scans show that the fishermen suffered damage.

Doctors strongly suspect that a microorganism, called pfisteria, is to blame. It produces a powerful toxin that can affect the central nervous system and interrupt the learning process in humans.

Not only were the brain scans of the fishermen abnormal, so were the results of some cognitive tests.

Doctors research pfisteria's effects with brain scans

For example, the fishermen in the study were asked to identify the colors of type printed in a list of words, while ignoring the words themselves. They had a harder time with the test than people who had not been exposed to pfisteria.

The good news is that three to six months after the fishermen stopped working in pfisteria-infested waters, their brain functions went back to normal.

And researchers at the University of Maryland say fish eaters and swimmers have nothing to worry about because it takes repeated exposures, day after day, to really affect the brain.

But infested waters are now required to be posted with signs, warning people to stay away.