Pfiesteria Linked to Thinking Problems
By David Brown
The problems go away in a few months, with cognitive ability returning to normal. Other signs of toxin exposure, such as skin sores, are less common than the mental changes.
The conclusions were reached by a team of Maryland researchers and are reported in tomorrow's edition of the Lancet. The study, the first of people with environmental exposure to pfiesteria to be published in a medical journal, supports earlier concerns that the unusual single-cell organism can pose health hazards to people.
The researchers examined and tested a small group of Eastern Shore residents, including eight fishermen, who were exposed last August during a fish kill on the Pocomoke River.
"I can tell you that in talking to them [as a physician], there clearly were difficulties," said J. Glenn Morris Jr., an infectious diseases specialist at the University of Maryland School of Medicine in Baltimore. "What we were able to show is that objective data in neurocognitive tests fits very well with the problems they were reporting."
Among the most heavily exposed, problems included not remembering where they were driving or for what purpose; forgetting they had done an errand, such as mailing a package; and, in the case of the watermen, finding themselves on board their boats without supplies they normally brought.
Pfiesteria, which was discovered in 1995, killed more than a billion fish in coastal North Caroli na over the past decade before striking Chesapeake Bay tributaries for the first time last summer. Maryland state officials briefly closed parts of the Pocomoke and adjacent waterways last August in response to pfiesteria-related fish kills there.
Last month, as many as a half-million fish died during one week-long attack in North Carolina's Neuse River. Although menhaden with pfiesteria-like sores were found last week on the Eastern Shore's Wicomico River and Shiles Creek, no serious outbreaks have occurred so far this year in Maryland or Virginia.
Morris and his colleagues at Johns Hopkins University and at the public health departments of Baltimore and Somerset County gave a battery of neurological and psychological tests to 19 men and women who reported health problems after contact with the Pocomoke during the fish kill. The exposures ranged from days on end for the watermen to brief visits by recreational boaters and biologists taking water samples. The exposed group was compared with an "occupationally matched" control group.
Both groups had slightly above average IQs, and no one in either group showed evidence of psychiatric illness. (One person in the original exposed group was removed from the study because of what appeared to be exaggerated symptoms.) On a dozen neuropsychological tests, the two groups scored virtually the same. On three, however, there were significant differences, with the heavily exposed people performing poorly compared with their counterparts in the control group.
In one of those tests, a person is given a list of 15 unrelated words and is asked to recall them later. This tests learning. In another, a person must concentrate on a confusing mixture of colors and words. This tests the ability to filter out extraneous information. In the third, fine-motor skills are tested by seeing how quickly a person can put shaped pegs in a pegboard.
In some cases, the scores were remarkably low. Most of the eight heavily exposed watermen, for example, scored worse in the word-recall test than 95 percent of the general population.
"They really had a very isolated deficiency in their learning ability," Morris said.
The researchers tested both groups again three months later. All but two of the people exposed to pfiesteria-laden water had test scores in the normal range. At six months, those two people had normal scores, also.
The exposed people also reported other symptoms. Some had headaches, others breathing problems and intestinal complaints. Four had skin sores of varying types. None of the physical findings was as consistent as the neuropsychological deficits.
Pfiesteria's toxin has not been purified, and the exact mechanism of its effects on the nervous system is not known.
Five people who had contact with estuarine waters in recent months reported health problems and called a hot line run by the Maryland Department of Health and Mental Hygiene are now being evaluated for possible pfiesteria exposure.
Staff writer Joby Warrick contributed to this report.
© Copyright 1998 The Washington Post Company