Seafood Safety
Life Cycle
The life cycle of codworm has been described by a number of authors
(Margolis, 1977; Hafsteinsson and Rizvi, 1987; Oshima, 1987). Adult
Pseudoterranova live in the digestive tracts of seals (especially grey
seals), sealions and walruses (Schantz, 1987). The eggs are passed in the feces
and develop to second stage larvae in seawater. The larvae are ingested by
crustaceans where they molt to the third larval stage. Fish become infected by
consuming infected crustaceans, and by serially passing the larvae from one fish
to another. When infected fish are eaten by marine mammals, the larvae attach to
the stomach and develop to fourth stage larvae and finally to the adult stage.
Humans are accidental hosts. They are infected by consuming raw or
undercooked fish contaminated with third stage larvae.
ADULT
------> Marine Mammals ------>
^ (seals, sealions, walruses) | Eggs released
| | in feces
| v
4th STAGE LARVAE 2nd STAGE LARVAE
Marine Mammals Seawater
^ |
| v
| 3rd STAGE LARVAE 3rd STAGE LARVAE
<------ Fish <------ Crustaceans
|
v
Humans (accidental hosts)Symptoms & Treatment
Pseudoterranova infections and Anisaksis infections are often
misdiagnosed or incorrectly reported. As a result, the symptoms of sealworm
infection may, in some documented cases, be exaggerated. It is generally
accepted that sealworm infections are less severe than Anisaksis infections
(Olson, 1986; McKerrow et al., 1988; Schnatz, 1989). According to one report,
there has only been one case in the U.S. where tissue penetration has occurred,
and 12 cases in which a larva was either coughed up or manually removed from the
mouth (Hafsteinsson and Rizvi, 1987). Other reports indicate more severe
symptoms caused by sealworm infections including, epigastric pain (sometimes
spasmodic and occurring every 3-10 minutes), sometimes accompanied by nausea,
vomiting and abdominal discomfort (Margolis, 1977). Animal experiments support
that Pseudoterranova is capable of penetrating the gastric mucosa,
however, penetration is usually superficial and involves only the head end of
the worm (Young and Lowe, 1969 as cited in Margolis, 1977).
Cases which require surgical removal of the parasite result in complete
recovery of the patient within hours to days. Anthelminthic drugs have not been
useful in treating codworm infections (Schantz, 1989). Since the nematodes do
not develop to maturity and produce eggs in humans, stool examinations are not a
useful diagnostic method (Deardorff et al., 1986; Schantz, 1989).
Statistics
Documentation and reporting of codworm infection is ambiguous.
Pseudoterranova decipiens look very similar to Anisakis, and the
symptoms of both infections are similar. As a result, cases are sometimes
misdiagnosed or incorrectly reported. Also, codworm infection is not reportable
to the CDC, so there is no definitive record of the number of cases. Prior to
1987, there have been 13 reported cases of codworm infection in this country
(Hafsteinsson and Rizvi, 1987).
Detection & Prevention
Candling is often used in processing plants to detect codworm larvae in
fillets. This technique is both time consuming and difficult since the larvae
are small and often blend in with the fish flesh. Studies have shown that
candling does not detect sealworms embedded deeper than 6mm in the fish
musculature (Hafsteinsson and Rizvi, 1987). Acoustic detection is currently
being developed, but it is still not commercially viable (Hafsteinsson and
Rizvi, 1987).
Freezing or cooking are the most effective methods of codworm prevention. If
the nematode is dead when consumed, it poses no threat to humans. Cooking the
fish to 140°F is sufficient to kill codworm larvae (USFDA, 1987). If the fish
will be eaten raw it is advisable to freeze it first. For home freezing fresh
fish, the temperature and time required to kill codworm larvae can depend on the
species of fish, the depth of penetration, and the physiological condition of
the larvae. The USFDA recommends freezing fish at - 10°F for at least 168 hours
(7 days) to kill codworm larvae (USFDA, 1987).
Eustrongylides
Description
Eustrongylides is a parasitic nematode, whose adult form parasitizes
the gastrointestinal tract of fish-eating birds. In the advanced larval stage
Eustrongylides is pinkish-red in color and can be as large as 40 mm in
length and 1 mm in width (Wittner et al., 1989).
Contaminated Species
Eustrongylides has not been reported in species of fish commonly eaten
by humans (Schantz, 1989). It is highly prevalent in brackish and freshwater
bait fish from Florida to Maine (Gunby, 1982). Minnows were examined for
Eustrongylides in two Baltimore area studies. One study reported a 33%
infection rate (Shirazian et al., 1984), the other study reported a 48%
infection rate (Gunby, 1982).
Life Cycle
The life cycle of Eustrongylides is not completely known. In the adult
stage, the nematode is found in the digestive tract of fish eating birds,
frequently great blue herons and egrets. Eggs are passed in the feces and
ingested by aquatic oligochaetes, the first intermediate host. Many species of
fish serve as the second intermediate host and a variety of amphibians, reptiles
and fish are the paratenic, or transport hosts. Eustrongylides develop to
advanced stage larvae in the body cavity and flesh of fish, amphibians and
reptiles (Cooper et al., 1978 as cited in Shirazian et al., 1984).
ADULT
------> Piscivorous Birds ------> Eggs passed
^ (herons & egrets) | in feces
| ^ |
| | v
Reptiles, Fish | LARVAE
and Amphibians | Oligochaetes
^ | |
| ADVANCED STAGE LARVAE v
<------ Fish <------
Symptoms & Treatment
Intestinal perforation by Eustrongylides results in severe abdominal
pain, gradually increasing with time. One individual has been successfully
treated with drugs (Shirazian et al., 1984), the other four reported cases
required surgery (Gunby, 1982; Schantz, 1989; Wittner et al., 1989).
Statistics
To date there have only been five reported cases of Eustrongylides
infection in humans. In 1982, three Baltimore area fishermen became ill after
consuming live bait fish (a practice of some anglers when the fish are not
biting) (Gunby, 1982; Shirazian et al., 1984). Two more cases were reported in
1989, involving a New Jersey fisherman who ingested live bait fish, and a New
York man who ate homemade sushi of uncertain fish variety (Schantz, 1989;
Wittner et al., 1989).
Detection & Prevention
Human infection of Eustrongylides can be avoided by not consuming live
bait fish. No precise information on temperature tolerance of
Eustrongylides is available (Wittner et al., 1989).
Diphyllobothrium
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