Pfiesteria

Pfiesteria piscicida (fee-STEER-ee-uh pis-kuh-SEED-uh) is a microscopic, polymorphic organism that belongs to a group of single-celled, free-swimming phytoplankton called dinoflagellates. Although many phytoplankton photosynthesize to generate the energy they need to survive, Pfiesteria does not—it is more animal-like in that it consumes other organisms such as bacteria and algae. It can transform in and out of the following stages within a matter of minutes: flagellated, amoeboid, and cyst. In the flagellated stage Pfiesteria is powered by two tiny flagella that resemble tails. The cyst stage lies dormant in the bottom sediments of estuaries and rivers.

Two species are known to release toxins that are harmful to aquatic and human life: Pfiesteria piscicida and Pfiesteria shumwayae.

When it was discovered in 1988, Pfiesteria was declared to be a new family (Pfiesteriaceae), genus (Pfiesteria ), and species (piscicida ), in the order Dinamoebales. It was named in honor of Dr. Lois Pfiester, an internationally respected researcher of dinoflagellates. Since its discovery, it has been identified in mud cores from the bottom of Chesapeake Bay that are at least 3,000 years old.

Depending on its stage, Pfiesteria piscicida, the most studied Pfiesteria species, ranges in size from about 5–450 microns in diameter. It is typically found in the bottom sediments and water of brackish tidal rivers and estuaries, primarily along the eastern seaboard of the United States.

Pfiesteria is a remarkably hardy organism that can survive over a wide range of temperatures and water salinities. For most of its life cycle Pfiesteria is a nontoxic predator, feeding on bacteria, algae, and other small organisms. When schools of fish are present, Pfiesteria occasionally responds with a quick release of biotoxins into the water. These chemicals stun or kill the fish, which allow the Pfiesteria to feed on the injured skin, blood, and dying tissue.

These toxic episodes last for several hours before dissipating, sometimes resulting in large-scale fish kills , many of which plagued the Atlantic coastline in the late 1980s and 1990s. Fish kills attributed to Pfiesteria occurred in estuaries in the Albemarle–Pamlico estuarine system in North Carolina, Chesapeake Bay tributaries in Virginia, the Chicamacomico, Pokomoke, and Manokin Rivers and King's Creek in Maryland, and Indian River in Delaware. Pfiesteria has been identified as far north as Long Island, New York, and as far west as the southern tip of Texas. It may also occur in Pacific waters along the California–Oregon–Washington coastline, but has not yet been identified because these waters have not been sampled.

Although Pfiesteria is technically not an algae, it's fish kills are usually included under the category of harmful algal blooms (HABs). This is because Pfiesteria shares many physiological and toxicological characteristics with the various algae species that cause algal blooms (red or brown tides), some of which are toxic to aquatic life.

Toxic strains of Pfisteria have been identified along European, Scandinavian, New Zealand, and Australia coastlines. It likely occurs in other international waters that have not been tested for its presence. As the technology of detection improves, it is highly probable the global distribution of Pfiesteria will become better defined. However, the United States is the only country in the world that has experienced the serious deleterious effects of its toxins on aquatic life and human health.

When Pfiesteria detects fish oils or excretions in the water from a large school of fish, a biological toxic response may be triggered. The organisms change from the cyst stage (excystment) into the predator flagellate or ameoboid stages, which then release potent toxins into the water.

The toxins penetrate the skin of the fish, creating bleeding ulcers. The fish become lethargic or die. The skin becomes so damaged that the fish cannot maintain their internal salt balance. The Pfiesteria organisms feed on the dead skin tissue, blood, and other fish fluids leaking into the water. Within several hours Pfiesteria transforms back to the cyst stage (encystment) and lays dormant in the bottom sediments. Fish kills usually occur in warmest times of the year and when the dissolved oxygen content of the water is low.

There has been a global increase in toxic and harmful algae blooms in the late twentieth century, including Pfiesteria. Modern technology increasingly allows for the rapid identification of the species causing the bloom or the fish kill. Pfiesteria attacks are becoming a growing problem because they have a negative impact on commercial fishing , recreation , and human health along the eastern seaboard.

Toxins can be present in the water or aerosolize into the air. Toxic episodes and fish kills close down sections of coastline, which impact the fish and shellfish industries. If fish aren't killed directly by Pfiesteria, they are seriously weakened, which makes them susceptible to other predators or bacterial and fungal infections. Humans can suffer serious health problems from coming into contact with, or inhaling, these biotoxins. Effects to humans and aquatic life persist for six to eight weeks after the bloom disappears.

Two kinds of toxins have been discovered to date: a fat-soluble toxin that blisters skin and a water-soluble toxin that affects the nervous system. Injection of Pfiesteria toxin has induced significant learning problems in laboratory rats. Symptoms in humans consist of lethargy, sores and rashes, eye sensitivity, headaches, blurred vision, gastrointestinal distress, nausea, memory loss, kidney and liver problems, shortness of breath, and fibromyalgia-like symptoms. Symptoms can recur for up to eight years after exposure. This condition, sometimes referred to as possible estuary-associated syndrome (PEAS) can be developed from exposure to Pfiesteria biotoxins, even if there is no evidence of fish kills or fish disease in the water.

Identifying a fish kill as being Pfiesteria -related (and taking subsequent actions, such as closing shorelines and issuing fish consumption warnings) can be difficult because Pfiesteria has 24 recognized morphological shapes at different growth stages. Scientists use light microscopes, bioassays, scanning electron microscopes, or polymerase chain reaction (PCR) methods to establish positive identifications.

An unanswered question remains: Are fish from areas that have experienced Pfiesteria outbreaks safe to consume? This may have significant impact to the fishing industry. So far research indicates that no person has become ill from eating fish or shellfish that have been exposed to Pfiesteria —the data, however, are limited. Most experts recommend to err on the side of caution: If an area has been closed because of a Pfiesteria outbreak, do not catch or consume fish from that area or swim or waterski in those waters for at least eight weeks after the outbreak.

Data suggest that Pfiesteria has a fairly wide global distribution, but only creates health problems under certain conditions, which seem to be best demonstrated in the coastal estuaries of the eastern and southern United States.

Research at North Carolina State University's Center of Applied Aquatic Ecology shows that Pfiesteria is stimulated by organic or inorganic nitrogen and phosphorus in the water—two key components of fertilizer . Carbon may also be a trigger substance. It has been documented that Pfiesteria outbreaks occur in areas that are downstream from septic tanks, sewage-plant discharges, agricultural waste such as excrement from cattle, swine, and poultry, and agricultural or landscaping chemical runoff . When these nutrients accumulate in slow-moving or stagnant sections of estuaries and mix with the incoming tidal water, Pfiesteria can become more active and toxic. Other stimulators may be airborne pollutants that settle in the water. An abundance of fish is also required. As yet it has not been determined if the nutrient loading stimulates the growth of the algae on which Pfiesteria feeds, or if directly stimulates Pfiesteria.

Federal organizations such as the U.S. Environmental Protection Agency (EPA), U.S.Department of Agriculture, U.S. Department of the Interior , National Oceanic and Atmospheric Administration , Centers for Disease Control and Prevention(CDC), and the National Institute of Environmental Health Sciences , state departments of health or natural resources , and several prominent university research centers are continuing research into the life cycles of Pfiesteria and other Pfiesteria -like organisms, their nutritional ecologies, and the trigger mechanisms that result in toxic episodes.

One major areas of study focuses on integrating management approaches with new emerging technologies. This collaborative effort between risk managers, universities, federal agencies, and users—commercial and recreational fishermen, Native peoples, and other water users—will lead toward a systematic approach to managing the risk for exposure to Pfiesteria biotoxins. The ultimate goal is to develop an accurate model of prediction—what conditions will result in toxic Pfiesteria /algal blooms? Knowing these factors may reduce or eliminate the need to close down sections of coastline and interrupt commercial fishing operations.

Researchers are also attempting to purify and study Pfiesteria biotoxins. When the actual toxin can be identified, it will be much easier to determine if fish kill/disease episodes are related to Pfiesteria attacks. Once the chemical signature of the toxin is identified, methods can be developed to test humans for exposure. Antitoxins or related drugs may also be developed. It is also possible that, when consumed or injected in prescribed dosages under certain conditions, Pfiesteria toxins may be useful medicines that reduce or alleviate other health conditions in humans.

[Mark J. Crawford ]

RESOURCES

PERIODICALS

Burkholder, J. M. "Overview and Present Status of the Toxic Pfiesteria Complex." Phycologia.

Burkholder, J. M., et al. "New 'Phantom' Dinoflagellate Is the Causative Agent of Major Estuarine Fish Kills." Nature 358 (1992): 407–410.

Burkholder, J. M. and H. B. Glasgow. "Pfiesteria piscicida and Other Toxic Pfiesteria -like Dinoflagellates: Behavior, Impacts, and Environmental Controls." Limnology & Oceanography. 42 (1997):1052–1075.

OTHER

Pfiesteria and Related Harmful Blooms: Natural Resources and Human Health Concerns. Pamphlet. U.S. Environmental Protection Agency, 1998.

What You Should Know about Pfiesteria piscicida. Document EPA 842-F-98-011. U.S. Environmental Protection Agency, 2002.

U.S. Department of Public Heath and Human Services.ldquo;Pfiesteria : From Biology to Public Health.rdquo; Environmental Health Perspectives 109 (2001): Supplement 5.

ORGANIZATIONS

Aquatic Pathobiology Center, University of Maryland, 8075 Greenmead Dr., College Park, MD USA 20742 (301)314-6808, Fax: (301)314-6855

Maryland Sea Grant, University of Maryland, 0112 Skinner Hall, College Park, MD USA 20742 (301)405-6371, Fax: (301)314-9581

North Carolina State University Center for Applied Aquatic Ecology, 620 Hutton Street, Suite 104, Raleigh, NC USA 27608 (919)515-3421, Fax: (919)513-3194

U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC USA 20460 (202)260-2090

Virginia Institute of Marine Science, Route 1208 Greate Road, Gloucester Point, VA USA 23062 (804)684-7000, Fax: (804)685-7097