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                       BIOINFORMATICS COLLOQUIUM
                    School of Computational Sciences
                        George Mason University
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                   Pfiesteria Hysteria: Fad or Fallacy

                            Patrick Gillevet
                        George Mason University

                        Tuesday, March 29, 2005
                               4:30 pm
               Verizon Auditorium, Prince William Campus

Pfiesteria piscicida is a heterotrophic dinoflagellate that has been
associated with fish mortalities and human health problems in estuaries
along the Atlantic shore of the United States since 1992.  This
association has relied on the detection of P. piscicida motile cells in
water samples collected from sites where fish mortality has occurred or
close to areas were individuals described unusual dermal, respiratory,
and neurological symptoms upon exposure to environmental water. It was
hypothesized that the ichthyocidal activity of P. piscicida was reported
to become apparent only when the vegetative forms (dinospores) emerge,
after exposure to fish, from resting cysts that are found in
environmental sediments. It has been further proposed that P. piscicida
produces one or more novel exotoxins that affect fish and other
organisms, including mammals.  The action of these toxins on fish
supposedly caused skin lesions, disrupt neural function, and eventually
lead to fish death.  It was concluded that this organism presented a
grave threat to to human health and the promotion of the "the cell from
hell" story had dramatic impacts on the tourist and seafood industries
in the Northeastern United States.

However, despite significant efforts over the past 13 years by numerous
laboratories, there are no definitive no reports on the isolation and
characterization of the toxin(s). The situation has been complicated
further by the description of non-toxic or temporarily non-toxic strains
that revert to toxicity under complex ill-defined conditions and by an
unusually complex life cycle composed of multiple stages (24) of
variable toxicity that are tied together in the so called Ambush
Predator Hypothesis.

To date, rigorous experimental data in support of all of the
aforementioned claims is lacking.  First, the actual existence of the
amoeba stage has been recently questioned in several detailed studies
ruling out the entire "Ambush Predator" hypothesis.  Secondly, recent in
vitro studies of the ichthyocidal activity of clonal P. piscicida in a
tank bioassay format indicated that active proliferation of the
dinospores can be associated with fish death but they require direct
physical contact with the fish ruling out the presence of exotoxins.
Thirdly, research has shown that the lesions observed in wild fish are
in fact caused by other infectious organisms.  Finally, a recent 5 year
study by the CDC has demonstrated that there are no neurological effects
in waterman exposed to estuarine waters.  We conclude that the entire
"Cell from Hell" hypothesis has not been based of rigorous, critically
reviewed science and is an classic example of how the complex
interaction between the scientific community, the press, public
perception, funding agencies, and regulatory agencies can influence the
progress of science.

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Refreshments are served at 4:00 pm.  Find the schedule and directions at
http://www.binf.gmu.edu/colloq.html