DNA Test Solving Chesapeake's Toxic Mysteries

David Oldach of the University of Maryland Biotechnology Institute (UMBI) reports that the test, applied to samples of mud or water, rapidly identifies Pfiesteria piscicida. In 1997, the microbe was linked with major fish kills in three Maryland rivers as well as previous fish kills in North Carolina. In addition, watermen near the fish kills and laboratory workers handling Pfiesteria cultures have suffered from illness ranging from skin lesions and stomach cramps to temporary memory loss and learning impairment lasting up to seven weeks.

In a recent issue of the Proceedings of the National Academy of Sciences, Oldach writes that the test is based on a "time-tested molecular biology method used commonly in medical research." The method, called HMA, is more often used to tease ut different strains of viruses in studies of Hepatitis C, AIDS, or gene mutations linked with cancer, or genetic diseases, such as cystic fibrosis.

Oldach and colleagues at UMBI's Institute of Human Virology (IHV) applied the method to samples of water and cultures of Pfiesteria-like microbes from Maine, Maryland, and North Carolina. The result is a DNA fingerprint of Pfiesteria used in the new test. The test can be adapted to detect other toxic marine organisms, he adds.

Last year in Maryland, experiments on the new test helped show that P. piscicida existed in at least 14 rivers and increased dramatically in July and August, according to Dave Goshorn, chief of the Maryland Department of Natural Resources' (DNR) Living Resource Assessment Program. "We found that the new test works so well, we will expand from 50 to 100 testing sites in the Bay area in 2000, in addition to any fish kill sites."

The new Pfiesteria test is "simple and brilliant," comments Robert A. Venezia, director of the state Department Health and Mental Hygiene's Office of Environmental Health Coordination. "The test has heightened the Department of Natural Resources' (DNR) ability to identify fish kills and subsequently issue an advisory for the public to avoid an area or to close the river," he adds.

The chemical structure of the P. piscicada toxin is still not "fully identified," says toxicologist John D. Ramsdell, who tests samples of Pfiesteria culture on brain tissues at the Charleston, S.C. laboratory of the National Oceanographic and Atmospheric Administration. However, he comments, "The work that Dave (Oldach) is performing to get the correct toxic organism has takenus light years ahead."

Ramsdell says the toxin affects immune cells in the brain. He says such a theory explains both the human memory problems and lethargy experienced by humans who come into contact with the toxin as well as the infectious lesions in the fish. Each Pfiesteria culture produces only a miniscule amount of toxin, he says, but stimulates "tremendous linkage in cells of the nervous systems."

Ultimately, says Oldach, the most important part of the Pfiesteria story may lie in medical studies of the toxicity. He notes, "The most exciting medical aspect is that reversible cognitive deficit (short-term memory loss), identified by Lynn Gratton, a neuropsychologist at the University of Maryland School of Medicine, relates to new learning -- the actual laying down of new memories." Oldach proposes that a small molecule, basically the toxin, may be disrupting a critical function in the brain that is essential for how people learn. Ragsdell adds that, because the toxin seems to work on a unique class of receptor or sensitive cells in the brain, the greatest potential of Pfiesteria research may be in new drugs for learning disorders.

Also, the new DNA test adds precision to studies of the health symptoms of watermen by Oldach and other medical researchers in the University System of Maryland and the Johns Hopkins School of Medicine. Every two weeks, participating watermen report their symptoms and areas where they have been working on the water. Two to three times a year, they take cognitive tests of their memory and concentrating powers. The results are in turn linked with DNR environmental data, including the presence or absence of Pfiesteria in the rivers, using the new test.

There have been no major outbreaks of toxic Pfiesteria since 1997. But, Maryland's DNR continues to seek answers to such questions as how to predict new outbreaks, when does the microbe turn toxic, and what is the nature of the toxin. The DNR will continue to send water samples to Oldach' laboratory, UMBI's Center of Marine Biotechnology (COMB), the University of Maryland's Center for Environmental Studies at Horn Point, and the Aquatic Botany Laboratory at North Carolina State University in an attempt to find more answers.