Seafood Safety

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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.
  ------> 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
              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).


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 140F 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 - 10F for at least 168 hours (7 days) to kill codworm larvae (USFDA, 1987).

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).
   ------> 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).

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).


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