May 24 - Anisakis simplex

If you suddenly experience a sharp abdominal pain and have recently eaten sushi, ceviche, or pickled herring, there's a chance you might have just become infected with Anisakis simplex. This species is a nematode that primarily uses marine mammals as its hosts. Eggs are excreted in feces, where they will then infect small crustaceans. There they mature into what are called L3 stage larvae. When the crustacean is eaten by a squid or a small fish, they will migrate to the muscle tissue and wait there for a mammal to eat that fish. If another fish eats it, they just repeat the process, and wait in the muscles of the second fish. When a whale, seal or dolphin eats the fish, the larvae mature into adults, mate, and lay eggs to begin the cycle all over again. Because a human body is - at least to these nematodes - about the same as a seal's, the worms can infect a person who eats an infected fish or squid. The result is pain, nausea, and/or vomiting, but as we humans are dead-end hosts, the treatment is usually just to relieve those symptoms and wait for the adult worms to die and pass. However, if individuals are sensitive to Immunoglobin E, however, ingestion of Anisakis can cause anaphylactic shock. Luckily these worms are fairly rare in the U.S., but cases do occur more frequently in Scandanavia, Japan, and western South America.

The photo is of L3 larvae in a herring.