What is Pfiesteria piscicida, and how do these organisms kill fish?

What is Pfiesteria piscicida, and how do these organisms kill fish? Should I be concerned where I swim?

—Rachael Monroe, Orlando, FL

Pfiesteria piscicida, a microbe, normally exists in rivers and bays in non-toxic forms, feeding on algae and bacteria. Scientists believe that this tiny creature becomes toxic only in the presence of fish, at which point Pfiesteria cells release a powerful poison that stuns fish and attacks their skin, causing bleeding sores. The attacking cells then feed on the fish tissues and blood. The U.S. Environmental Protection Agency (EPA) estimates that millions of fish are killed this way each year.

Pfiesteria growth exploded in the late 1990s in waters that became too “nutrient-enriched,” i.e. polluted by sewage treatment plants and by farms that allow excessive runoff of fertilizer and animal manure. In the U.S., the phenomenon seems to be isolated on the east coast, where waters are warmer and less turbulent, supporting more bacterial growth for Pfiesteria to feed on.

Pfiesteria populations have been found from New York to the Gulf of Mexico, with the largest concentrations in the Cheasapeake Bay and off the coast of North Carolina. “North Carolina is the best place for Pfiesteria problems because the waters off the outer banks, a series of barrier islands, are shallow, warmer and poorly flushed,” says scientist JoAnn Burkholder at North Carolina State University. However, in 1999 Hurricane Floyd scoured North Carolina”s shoreline and estuaries, reducing the number of Pfiesteria colonies there.

As to Pfiesteria”s affects on human health, evidence suggests that exposure to waters or airborne vapors where toxic forms of Pfiesteria are active may cause memory loss, confusion and a variety of other symptoms including skin sores and respiratory and gastro-intestinal problems. However, Pfiesteria is not a virus, fungus or form of bacteria. It is not contagious or infectious, and cannot be “caught” like a cold or fluand there is no evidence that Pfiesteria-related illnesses are associated with the consumption fish.

The Centers for Disease Control and Prevention, in cooperation with state health departments in Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina and Virginia, have established a surveillance system to collect reports of human illness thought to be related to exposure to Pfiesteria and Pfiesteria-like organisms. This and other ongoing research efforts are expected to further delineate the nature, extent and duration of any Pfiesteria-related human health effects. In the meantime, Burkholder says, “If you see a fish kill, avoid the area and call state biologists to check it out.”

CONTACTS: Center for Applied Aquatic Ecology, North Carolina State University, (919) 515-2726, http://www.pfiesteria.org/pfiesteria/index.html; U.S. Environmental Protection Agency, http://www.epa.gov/owow/estuaries/pfiesteria; Centers for Disease Control and Prevention, (404) 639-3534, http://www.cdc.gov.