THE CELL FROM HELL

WHAT IS PFIESTERIA

Pfiesteria piscicida (fee-STEER-ee-uh pis-kuh-SEED-uh) is a toxic dinoflagellate that has been associated with fish lesions and fish kills in coastal waters from Delaware to North Carolina. A natural part of the marine environment, dinoflagellates are microscopic, free-swimming, single-celled organisms, usually classified as a type of alga. The vast majority of dinoflagellates are not toxic. Although many dinoflagellates are plant-like and obtain energy by photosynthesis, others, including Pfiesteria, are more animal-like and acquire some or all of their energy by eating other organisms.

Discovered in 1988 by researchers at North Carolina State University, Pfiesteria piscicida is now known to have a highly complex life-cycle with 24 reported forms, a few of which can produce toxins. Three typical forms are shown on the right. A few other toxic dinoflagellate species with characteristics similar to Pfiesteria have been identified but not yet named. These are referred to as "Pfiesteria-like organisms," and they occur from Delaware to the Gulf of Mexico.

HOW DOES PFIESTERIA EFFECT THE FISH?

Pfiesteria normally exists in non-toxic forms, feeding on algae and bacteria in the water and in sediments of tidal rivers and estuaries. Scientists believe that Pfiesteria only becomes toxic in the presence of fish, particularly schooling fish like Atlantic menhaden, triggered by their secretions or excrement in the water. At that point, Pfiesteria cells shift forms and begin emitting a powerful toxin that stuns the fish, making them lethargic. Other toxins are believed to break down fish skin tissue, opening bleeding sores or lesions. The toxins or subsequent lesions are frequently fatal to the fish. Fish may also die without developing lesions. As fish are incapacitated, the Pfiesteria cells feed on their tissues and blood. Pfiesteria is NOT an infectious agent like some bacteria, viruses, and fungi. Thus, fish are NOT killed by an infection of Pfiesteria, but rather by the toxins it releases, or by secondary infections that attack the fish once the toxins have caused lesions to develop.

HUMAN HEALTH

Very little research on the human health effects of Pfiesteria toxins has been conducted. At a multi-state workshop at the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, at the end of September 1997, attendees agreed on clinical symptoms that characterize the adverse health consequences of exposure to Pfiesteria toxins. These clinical features include: 1) memory loss; 2) confusion; 3) acute skin burning (on direct contact with water); or 4) three or more of an additional set of conditions (headaches, skin rash, eye irritation, upper respiratory irritation, muscle cramps, and gastrointestinal complaints (i.e., nausea, vomiting, diarrhea, and/or abdominal cramps). With these criteria and environmental qualifiers (e.g., 20% of a 50-fish sample, all of the same species, have lesions caused by a toxin), it is likely that Pfiesteria-related surveillance data can better track potential illnesses. Pfiesteria toxins have been blamed for causing adverse health effects in people who have come in close contact with waters where this organism is abundant. Since June 1997, the Maryland Department of Health and Hygiene has been collecting data from Maryland physicians through a state-wide surveillance system on illnesses suspected of being caused by Pfiesteria toxin. As of late October 1997, illness was reported by 146 persons who had been exposed to diseased fish or to waters that were the site of suspected Pfiesteria activity. Many of these persons are watermen and commercial fishermen. The strongest evidence of adverse human health effects so far comes from case studies of two research scientists who were both overcome in their North Carolina laboratory in 1993. They still complain of adverse effects on their cognitive abilities, particularly after exercising. Duke University Medical Center researchers conducted experiments on rats, which showed that the toxin appeared to slow learning but did not affect memory.