When Glenn Morris and his medical team climbed aboard the van that muggy August morning, they were embarking unknowingly on a 10-year road trip full of discoveries, unexpected detours, and more than a few dead ends. The destination seemed clear enough at first — figure out what was making people sick — but over the next decade the goal seemed to retreat down the road before them like a water mirage disappearing in the distance.

Some holes in their science case are still there. What happened, for example, in the brains of people exposed to a toxin from the Pocomoke, a toxin that chemists struggled for over a decade to identify. Without a toxin sample to work with, the medical team tried techniques like high-tech scans of human brains and lab studies of rat brains, but the best they got from all this work were hints and hypotheses for further testing.

From the brain scans came hints that the Pocomoke toxin may slow down brain areas like the hippocampus, one of the sites for short-term memory. From the rat brain studies came evidence the toxin may turn off a neuroreceptor (the NMDA receptor) that receives signals aimed at the hippocampus and other memory structures. Short-term memory loss in that case could come from poor communication at the cellular level in the brain, according to Morris. New information comes in but new memory is never laid down. As far as your brain is concerned, the job you just started, the conversation you just had, this article you've been reading — all those events never happened.

Short-term memory loss was, luckily, not a long-term event for people along the Pocomoke. When they were retested, three months after their exposures, most of the Pocomoke patients were again scoring within normal range on their memory tests, and at six months all the patients had improved enough to bring their scores within national norms for their age and gender. Whether they all came all the way back, however, remains another unanswered question.

Did Pfiesteria pose a major public health threat? With Pfiesteria DNA turning up all around the Bay, the Morris-led team pinned their highest hopes for a clear answer on a classic research tool called a "cohort study," an epidemiological study designed to give a definitive "Yes or No" sort of answer.

The basic idea was a before-and-after study tracking a group of watermen, a "cohort" that was likely to be exposed to water with fish and Pfiesteria. Over four years, they would test watermen at the beginning of each work season, creating a baseline on their medical status, much as your family doctor does with your annual physical. By retesting at the end of the season — and during the season if anyone was encountering toxic blooms or developing symptoms — the team could see any changes pointing to a Pfiesteria-like health effect. The expected results should be the cleanest data yet on how Pfiesteria affected anybody working the Bay.

The unexpected result, however, was four years with no documented toxic Pfiesteria blooms, no large fish kill episodes, no reports of new episodes of neurocognitive deficits. Fish kills occurred in the Bay, but none of them broke out near the watermen in the study group. Pfiesteria might be all over the Bay, but it seemed to have stopped forming toxic blooms.

That was bad news for the researchers, but good news for the Bay's watermen, state workers, and waterskiers. No new cases came from this cohort group, not even from all those watermen clocking heavy work weeks on the water. The study began with 123 test-case watermen and finished up with 88 who hung in for four years of twice-yearly testing and biweekly reporting. During those years state officials and watermen took 3,500 samples from the waters they were working, and Pfiesteria showed up in 110 or 3.2 percent of the samples.

Those are samples large enough for strong conclusions, and the strongest, according to Morris, is that Pfiesteria is not a health threat to working watermen — or probably to anybody else. "For the average waterman or Sunday boater," says Morris, "I would say with a high degree of confidence, there is no risk."

That "no risk" finding — based on 88 people — has drawn criticism, especially from Ritchie Shoemaker, the doctor from Pocomoke City who first began diagnosing a Pfiesteria-like syndrome back in 1997. Six dropouts from the cohort study came to see Shoemaker, claiming they were sick with classic symptoms of toxic exposure. "Seven percent of the people they followed got sick," says Shoemaker. The cohort study, he also points out, failed to track recreational boaters and waterside residents. Shoemaker estimates 20 people have come to him over the last six years with symptoms from low-level exposures to toxins in the water.

Over the last decade, however, the estimate of cases from Maryland waters remained low. The question that Morris and his team first set out to answer — Is there a major public health risk? — seems to have a new answer. Nine years after 1997, his Yes answer had become a No.

That answer leaves a large question: whatever happened to the watermen and state workers on the Pocomoke River?

"Pfiesteria ten years ago still remains an intriguing and puzzling mystery." says Morris, sitting in his office in Baltimore still looking trim and calm, if slightly grayer, his high hopes dwindling into some humility in the face of the unexplained. "It is very frustrating in today's world with the sophistication of science today not to be able to explain what happened."

A lot of science happened over the last decade, he points out, and some of it produced useful findings. The cohort study came up with a "good news" finding that is important for policy makers as well as for watermen and waterskiers and boaters. Rat studies showed evidence that Pfiesteria diminishes new learning, at least among rats running a maze, and they turned up clues about how toxins affect neuroreceptors.

That's good progress, but the sick-people question remains unanswered. "I have to agree with Glenn. We just don't know," says Oldach, whose DNA probe put a new technique in the tool box of marine biologists and field workers.

Both will tell you the Pocomoke syndrome was not "Pfiesteria hysteria," their original hypothesis. "There was no mass hysteria," says Morris. This wasn't the kind of population likely to experience mass psychogenic illness, he explains. The similar stories, the testing, the screening — all this evidence convinces him. The finding was too specific, too focused for people to fake. "There was a real event on the Pocomoke," he says, "but whether it was related to Pfiesteria, I have no idea."

Both scientists agree that another toxic event could happen, either in the Pocomoke or elsewhere, even though it hasn't happened again in the last 10 years. "Perhaps we have to think of Pfiesteria events like this as a 25-year storm," Oldach says. "Or a 100-year storm."

The Pfiesteria next time will probably not bring on another Pocomoke syndrome. "The Pocomoke was a unique natural experiment," says Morris. "People kept being told, �It's okay. There's no problem. Go back. Keep working.' So we had people who were constantly being exposed to the point that there were profound deficits."

Thanks to fast findings from new DNA probes, state officials can now close a river before people suffer repeat exposures. "Ethically," says Morris, "we can never let that happen again." The uncontrolled experiment is over.

At the end of the research road then a classic Catch 22 was lying in wait for Morris and his medical team. Thanks to the progress of science, there may be no more progress on the science question that started them down the road.

Scientists may not have many more subjects to study, or more natural experiments that might help them answer the question that first took them into the field.

"I can't tell you what happened in the Pocomoke in 1997," says Morris, "And I'm not sure I'm ever going to be able to tell you."

A note on sources: Descriptions of events and reactions were drawn from personal reporting and multiple interviews conducted with participants and experts between 1997 and 2007. For a list of articles consulted, go to www.mdsg.umd.edu/Pfiesteria.

This page was last modified September 15, 2018