Saturday, July 15, 2023

Answer to Case 722

Answer to the Parasite Case of the Week 722: anisakid larvae, one of the members of the Anisakis simplex, Pseudoterranova decipiens, or Contracecum osculatum complex. 

Humans can become transiently infected with the larvae when they are ingested in undercooked fish, such as this salmon. The larvae may embed in the gastric or intestinal mucosa, causing intense pain. Endoscopic removal is curative. In less severe cases, the larvae will migrate back up the esophagus and out the mouth - a much preferred (but disturbing!) alternative. They can also be passed in the stool. In these settings, the larvae have to be differentiated from immature Ascaris lumbricoides. This can be accomplished using a number of morphologic features. 

To avoid anisakiasis, Chia-Yu Chiu wisely notes that the FDA recommends that salmon (and all fish) should be well-cooked or frozen prior to ingesting to kill the larvae.  This case is a good example of how fish is not always frozen prior to sale - even in a well known grocery chain. Therefore, it is up to the consumer to freeze the fish prior to eating raw! The FDA recommends freezing for 7 days using a standard, consumer-grade freezer (-20℃). Restaurants usually freeze for 24 hours or less at -70℃. 

On a final note, some people develop an allergy to anisakids, and therefore even freezing won't protect from allergic reactions following consumption. Individuals with severe anisakid allergies may have to avoid ocean fish indefinitely.


Anonymous said...

If killed by freezing or cooking, are they visible on the "way out"?

ParasiteGal said...

They can be I suppose, if they don't get chewed up and digested in the process. However, I doubt they would be easily identified in all of the fecal material!