Effects of Pfiesteria on humans becoming clearer, scientists say But chemical identification of the toxins produced by the microbe is still needed

September 18, 1997|By Douglas M. Birch | Douglas M. Birch,SUN STAFF

Scientists studying the health effects of the microbe suspected of killing fish in East Coast waterways say that a clear picture is emerging about the threat to humans.

"This is not that mysterious," said Dr. Donald E. Schmechel of Duke University, who studied the first human cases of poisoning by Pfiesteria piscicida. "This has a gun and smoke coming out of the barrel. The question is, what is the bullet made of?"

And how much damage can it inflict?

This much seems known: There is a strong link between an array of symptoms -- short-term memory loss, skin rashes and respiratory problems -- and exposure to waters where Pfiesteria-like organisms are attacking fish.

This much is suspected: That people can be exposed to the organisms' toxins by swallowing, touching or just breathing the mist from those waters. And that people probably can't get sick from eating fish that have survived or shellfish nearby.

Otherwise, "our impression is that there should be a lot more people ill," said Trish M. Perl, an infectious disease specialist at the Johns Hopkins School of Medicine. "How many people eat seafood in Maryland?"

Swimming and fishing are probably safe where there are no fish kills, researchers say.

"People in Maryland are freaked out about eating fish or going in the water," said Schmechel. "To me, that's an overreaction."

"How severe can it be?" asked Perl, part of a team that studied suspected cases of Pfiesteria exposure on the Pocomoke River. "How mild? How long does it last? Is it permanent? Is it reversible? How much exposure does it require? If you step in the water, is that enough? If you go swimming, is that enough?"

From the viewpoint of the scientist, the single most important step toward discovering how Pfiesteria affects humans would be chemical identification of toxins produced by the microbe.

The microbe and its near relations may produce a cocktail of perhaps a dozen chemicals. None has been described.

"To make significant progress in diagnosis and understanding what these things do, you have to chemically identify what you're dealing with," said Schmechel of Duke's Neurological Disorders Clinic in Durham, N.C. "No one knows the exact nature of it yet."

Still, some of the microbe's effects are being identified.

Dr. Ed Levin, director of the toxicology program at Duke's Neurobehavioral Research Laboratory, has injected lab rats with Pfiesteria-contaminated water and run them through a maze.

In a paper to be published in Environmental Health Perspectives, Levin reports that rats receiving a single injection suffer a significant learning deficit that lasts at least 10 weeks.

The toxins don't appear to damage the rats' established memories. They can recall things learned earlier. They just have trouble learning new mazes.

Whatever Pfiesteria produces, it does not appear to be lethal to lab animals. Levin has not found a dose big enough to kill them.

"The rats are quite healthy and happy, to look at them," he said. "They're not obviously impaired."

Levin wants to find the smallest dose that can cause sickness and to see whether a given method of exposure produces a particular symptom.

Does breathing an aerosol of the toxins, he asked, produce shortness of breath while skin exposure produces sores or lesions?

Schmechel treated Dr. JoAnn Burkholder, who discovered Pfiesteria, her student Howard Glasgow and a third researcher at North Carolina State University in the early 1990s. They were the first known cases of Pfiesteria poisoning.

He also examined five cases among commercial fishermen and others working on the Neuse River near New Bern, N.C.

"In none of those cases were we able to come up with a clean picture," he said.

But last month, a Maryland physician referred two cases from the Pocomoke River area. Both had clear-cut symptoms, he said. And those symptoms meshed perfectly with what he saw in treating Burkholder and the others exposed in her laboratory.

One Maryland case involving a water-skier suggests two things, he said. First, that people can be exposed to the microbe's toxins by breathing the spray from contaminated waters. Second, he said, some people seem to be more sensitive than others.

Other skiers were on the Pocomoke about the same time. None reported similar complaints.

In both Maryland cases, symptoms decreased significantly in days. Burkholder, though, still feels the effects, including recurring bouts of a flu-like illness.

Long-term health effects "are possible," Schmechel said.

Burkholder, Schmechel noted, suffered a "massive" dose. Outside the laboratory, exposure levels are likely to be much lower, he said.

"While there may be mild persistent defects or problems, this seems to be a reversible situation," he said.

Pub Date: 9/18/97

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