Fundamental Food Microbiology, Third Edition - Fuad Fathir

OPPORTUNISTIC PATHOGENS, PARASITES, AND ALGAL TOXINS 411
B. Shellfish Poisoning
1. Paralytic Shellfish Poisoning
Scallops, clams, and mussels feeding on Gonyaulax catenella and related toxic
species of algae accumulate heat-stable toxin in the tissues. Consumption of these
shellfish produces paralytic poisoning. The common neurological symptoms include
tingling and numbness of lips and fingertips, drowsiness, poor coordination, incoherent
speech, and dryness of the throat. In extreme cases, respiratory failure and
death can result. The symptoms appear within 1 h and subside within a few days.
Occurrence of paralytic shellfish poisoning is sporadic and depends on the growth
(bloom) of the toxic algae, as influenced by water temperature (ca. 8�C), salinity,
run-off, presence of nutrients, and others. Shellfish growing in shallow water tend
to accumulate more toxins. In the U.S., the incidence of paralytic shellfish poisoning
is quite low. Between 1973 and 1987, there were only 21 incidents affecting 160
people. Between 1983 and 1987, only 2 incidents were reported. This has been
possible because of monitoring systems of shellfish for toxins and closing contaminated
shellfish beds for harvesting. 8–10
2. Neurotoxic Shellfish Poisoning
Growth of the toxic algae Ptychodiscus brevis produces red tide, and feeding of the
algae by shellfish causes them to accumulate toxin in the muscle. Consumption of
these shellfish produces neurological symptoms as described for paralytic shellfish
poisoning, but less severe. The symptoms appear very quickly and generally subside
in a few hours. The incidence is very low in the U.S. because of effective monitoring
systems. 8–10
3. Diarrhetic Shellfish Poisoning
Gastrointestinal disorders from the consumption of scallops, mussels, and clams that
feed on the toxic algae Dinophysis fortii were reported in Japan and the Netherlands.
The duration of the symptoms is short. The toxin is heat-stable, and thus cooking
does not eliminate it. The incidence of the disease can be reduced by removing the
digestive organs of the shellfish, because they tend to accumulate the majority of
the toxins. 8–10
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V. PARASITES
Included in this group are several intestinal and tissue helminths (roundworms,
flatworms, and tapeworms) and protozoa that are known to cause human illness and
where a food association has either been confirmed or suspected. They can stay in
the GI tract and produce gastrointestinal symptoms. Some invade body tissues and
produce specific problems. Several of these organisms and the diseases they produce
are briefly described here.