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Response to Potential Human Health Threats Posed by Pfiesteria Piscicida

Statement of

Fred R. Shank, Ph.D.
Center for Food Safety and Applied Nutrition
Food and Drug Administration
Department of Health and Human Services


the Subcommittee on Human Resources
House Committee on Government Reform and Oversight

September 25, 1997

Mr. Chairman and members of the Committee:

I am Fred Shank, Ph.D., Director of the Food and Drug Administration's Center for Food Safety and Applied Nutrition (CFSAN). I am accompanied today by Dr. George Hoskin and Dr. Sherwood Hall of our Office of Seafood. We appreciate this opportunity to participate in today's hearing on the federal response to the potential human health threats posed by Pfiesteria piscicida.

The Committee asked for FDA?s testimony on the potential human health threats that may be posed by Pfiesteria via human consumption of seafood.

As I will address in more detail below, there have been no reported illnesses confirmed or otherwise, attributed to seafood exposed to Pfiesteria. As you know, the initial event that identified Pfiesteria as a potential problem in Maryland was the fish kill in the Pocomoke River. Concerns also were raised because of the reported effects on people from waters containing the organism, i.e., from environmental exposure.

From the outset, FDA has been concerned about the possible food safety implications of Pfiesteria. FDA seafood research scientists have been closely following developments related to Pfiesteria since it was first described in North Carolina in 1991. Our scientists have maintained direct and on-going dialogue with other researchers studying the organism.

Early reports were that Pfiesteria is toxic to virtually all species of finfish as well as to scallops and clams. Human illness from consumption of finfish seems improbable, however, because finfish are killed so rapidly that they are unlikely to accumulate toxin and because the affected fish are so unattractive due to bleeding sores, it is doubtful they would be consumed. FDA has examined crabs taken from the Pocomoke River in which a fish kill occurred and found no evidence of toxicity attributable to Pfiesteria. From recent discussions with Dr. JoAnn Burkholder, the scientist that identified this organism, however, FDA has confirmed that oysters survive in the laboratory in the presence of the Pfiesteria organism. Oysters may, therefore, be capable of accumulating Pfiesteria toxins and posing at least a hypothetical health risk to humans. There is no proof as yet that Pfiesteria toxin accumulates in oysters so that they would be dangerous to ingest, but we are actively researching this possibility.

As background for the Committee, we will now briefly outline the federal structure for the regulation of seafood safety.


FDA is one of the primary Federal regulatory agencies responsible for the safety of edible seafood in the United States. Other agencies include the National Oceanic and Atmospheric Administration (NOAA) of the Department of Commerce, and the Environmental Protection Agency (EPA).

NOAA has the authority to close Federal waters to fishing whenever oil spills, toxic blooms, or other phenomena threaten the safety of the harvest. FDA and NOAA work closely together under such circumstances. EPA is responsible for water and air quality that can affect whether edible fish species are safe to eat.

FDA is responsible for implementing both the Federal Food, Drug, and Cosmetic (FDC) Act and the Public Health Service Act. The FDC Act in part, prohibits interstate shipment of adulterated and misbranded food, including seafood. The Public Health Service Act authorizes FDA to use appropriate measures to prevent the spread of communicable diseases. Under the FDC Act, a food is adulterated if it contains any substance that poses a reasonable possibility that the food is injurious to human health, or if quality defects affect its fitness as food.

To support its regulatory mission, FDA has 15 field laboratories that can analyze seafood samples for contaminants. Additionally, the Agency has state-of-the-art research facilities dedicated solely to seafood, as well as some of the world's leading experts in marine toxins and other specialties as Agency employees.


FDA has a vigorous seafood research program that supports the agency?s regulatory mission. FDA research forms the basis for the Agency's understanding of the extent and severity of hazards, for risk assessment, and for risk management. Seafood research is carried out at FDA's Gulf Coast Seafood Laboratory at Dauphin Island, Alabama; the Seafood Products Research Center in Washington State; as well as in FDA laboratories, located in both headquarters and field sites.

FDA currently has research scientists working on projects relating to seafood hazards posed by microorganisms, chemical and drug residues, marine toxins, parasites, decomposition, and new packaging technologies, as well as research on species identification; and the potential health implications of poor sanitation and filth contamination. Broader research of food safety, including toxicology, microbiology, chemical and pesticide residue research also applies to seafood.

We coordinate our research with ongoing research outside the Agency, working with academia and with other government and private organizations. In particular, we maintain an active dialogue with researchers working at the National Marine Fisheries Service of the Department of Commerce.


The Federal government could not effectively regulate seafood without the existence and cooperation of State programs. The several roles played by the States in the regulation of seafood are crucial to the overall success of the Federal/State program.

One of the key elements of FDA's Federal/State program is the National Shellfish Sanitation Program (NSSP). The NSSP is a Federal/State/industry endeavor, involving 23 shellfish producing States, several non-producing States, and nine foreign governments. The organization was established for the purpose of exercising control over all sanitation aspects of growing, harvesting, shucking, packing, and interstate transportation of molluscan shellfish. The Interstate Shellfish Sanitation Conference (ISSC), an organization of Federal agencies, State officials, and the shellfish industry, works with FDA to establish uniform guidelines and procedures that are used by the shellfish control agencies of the States. The NSSP and the ISSC operate together as a vital adjunct to Federal seafood safety programs.

The key to ensuring that molluscan shellfish do not carry pathogens from water pollution is the proper classification and monitoring of shellfish growing waters. FDA is responsible for helping to design and review the actions states take to classify their waters. States are required to take measures to ensure that illegal harvesting does not occur from closed waters and to certify that shippers operate in a sanitary manner.


Pfiesteria are dinoflagellate algae. Dinoflagellates are unicellular organisms which exhibit a great diversity of form. They have flagella that permit them to move in the water. The largest organism of this class may be as large as 2 mm in diameter, and the smallest is invisible to the naked eye. Though not large by human standards, these creatures can have a big impact on the environment around them. Many are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food source for other organisms. Others are able to feed on organic particles and even on other algae cells.

Some algae are known to reproduce suddenly in very large numbers and they can be seen as a mass or ?bloom? in the water. These species reproduce in such great numbers that the water may appear golden or red, producing a "red tide." These blooms occur when conditions, such as temperature, salinity, and nutrients, are conducive for their growth, usually during the summer. Marine life in the vicinity of the bloom may suffer due to depleted amounts of oxygen in the water. Also, some dinoflagellates produce toxins that affect fish and humans directly or through consumption of seafood. Some of the better known human illnesses originating from dinoflagellates are ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating affected shellfish, such as clams, mussels, and oysters).

Toxic blooms which can occur on all coasts of the United States, constitute a public health problem because of their unpredictability and the rapidity with which concentrations of toxins may develop. These toxins can affect shellfish as well as some finfish. At present, the only available public health measures are surveillance and closure of harvest areas for affected seafood species when blooms are detected.

Fish kills from natural causes occur for many reasons, most commonly due to reduced oxygen levels in the water caused by the algal bloom. Only recently have fish kills been attributable to toxins produced by Pfiesteria. In the fish kills in Maryland, examination of water samples has confirmed the presence of Pfiesteria piscicida, but also of other new species of Pfiesteria about which even less is known.


Since the first reports of this organism were received, researchers at FDA have maintained a dialogue, followed the literature, and otherwise kept abreast of the progress on understanding the biology and possible toxic properties of Pfiesteria. Throughout this time controversies, typical of scientific inquiry, occurred over such fundamental questions as whether the organism actually produced toxin and whether toxin was involved in fish kills associated with the presence of the dinoflagellate.

To date, no evidence has been identified to suggest a hazard from human consumption of seafood associated with Pfiesteria.

While seafood-consuming animals (wildlife, livestock, domestic animals) have tended to be visibly affected during other marine biotoxin outbreaks, no animal illnesses have been reported in affected areas of North Carolina or the Chesapeake Bay.

Since the appearance of the algal bloom in Maryland there have been several meetings involving Federal, state, and private/academic participants. A colloquium on the lesions appearing on the fish in the Pocomoke River was held August 1-3 sponsored by the Office of the Governor of Maryland. This meeting assessed the information available regarding unusual numbers of lesions on fish from some areas as well as complaints of unusual illnesses and skin problems suffered by area watermen. The possible role of Pfiesteria was of particular concern. A technical group was asked to critique research proposals prepared by several Maryland Departments for environmental and other studies on the extent and causes of the reported problems. FDA was asked to participate on the Technical Committee and on the Public Health Committee.

Regarding effects on humans, the Maryland Health Department has undertaken active follow-up on the individuals reporting health problems, and the federal Centers for Disease Control and Prevention (CDC) is working to establish a "case definition" or "syndrome" to be used to identify and monitor adverse effects on humans from environmental exposure.

Little is known about the toxins produced by Pfiesteria or of the ecological fate of such toxins. Reports from North Carolina suggest that toxicity disappears from water as rapidly as 24 hours after a fish kill. The toxins of Pfiesteria have not yet been chemically defined, but evidence indicates that there are at least two different types of toxin that may have effects through environmental exposure on animals and humans. Data from Maryland supports a central nervous system effect, and skin lesions reported by watermen may be from contact with water containing the toxin.

A protocol to assay seafood for toxicity has been prepared by FDA and samples from environmental and controlled laboratory exposures to Pfiesteria are being examined. Researchers in other laboratories are attempting to isolate and characterize Pfiesteria toxins. As better knowledge of specific toxins becomes available, the ability to determine seafood hazards will become more precise. At present, faced with unknown toxins, the only means to determine potential seafood safety hazards are generalized chemical and bioassay tests.

In discussions at the meeting in early August, a leading researcher on Pfiesteria stated that while most animals seem to die in the presence of the toxin (at least in the laboratory tanks), oysters in the laboratory continued to filter feed in its presence. This observation raises the question of whether oysters can acquire the toxin and might, at least hypothetically become toxic to human consumers. Based upon this observation, FDA initiated food safety studies of oysters. We have asked the State of Maryland to provide specimens of shellfish (both molluscan and crustacean) from fish kill areas. To date, the State of Maryland has provided crabs from the mouth of the Pocomoke River where the recent outbreaks have been most intense. As mentioned earlier, FDA analysis found no evidence of toxicity in the crab attributable to Pfiesteria. It should be noted that to the best of our knowledge, there are no harvestable molluscan shellfish beds in the North Carolina or Maryland areas where Pfiesteria-linked fish kills have occurred.

We also asked Dr. Burkholder to provide oysters exposed to cultured Pfiesteria in her laboratory tanks. On September 16, we received the first two experimentally-exposed oysters from that laboratory for toxicity assessment by FDA?s Washington Seafood Laboratory. We expect to have preliminary results regarding the toxicity of oysters in a few weeks.

We are pleased to keep the subcommittee informed as information on the effects of Pfiesteria on seafood develops.

My colleagues and I will be pleased to answer any questions that you may have.