Anisakiasis

Another of our favorite worms that really don't want to be in humans! Anisakiasis is a problem caused by Anisakid nematodes, typically Anisakis spp. or Pseudoterranova spp. Their preferred host (principal host) are fish eating mammals, such as dolphins. While we don't see many cases of humans becoming infected from eating dolphin meat, what we do see is people getting infected from eating raw fish, especially in the case of sushi. While any restaurant in the US that serves sushi must serve sushi grade fish, which has been frozen to a degree that any parasites die, restaurants outside of the US do not have this same regulation. While this infection has been found worldwide, it is obviously more common in areas where raw fish is frequently consumed.

Pathology with Anisakiasis most often presents in one of two ways, typically corresponding with the two most common types of species, though either can present in either way. The non-invasive type, typically found with Pseudoterranova spp., usually is asymptomatic until the infected person coughs up a worm. (Surprise!) There is no tissue penetration in this type of infection. Once the worm is coughed up, no further action needs to be taken, apart from some possible counseling to deal with having coughed a fully formed half centimeter worm out of your throat.

Photo Credit: Stanford.edu

These can get up to 2cm!

The other type of infection is invasive, and is typically caused by the Anisakis spp. With the invasive type of infection, the larvae attach to, embed themselves in, and penetrate tissues, typically in the intestine. This presents as extremely severe pain in the abdomen, similar to a ruptured appendix, though it can be sometimes more mild. In these cases, the worm is typically removed with surgery, as most anti-helminthic drugs are not useful once the larva has penetrated an organs. This can be differentiated from other types of abdominal pain because it comes on extremely suddenly and strongly a few hours after ingesting the infected fish.

Unless you want to carefully inspect every piece of sushi before you eat it, not eating raw fish outside of the US can prevent this infection. Proper freezing, cooking, and preparation of seafood will prevent this infection.

In the US, there tend to be less than 10 cases per year, due to the restrictions placed on fish. In places where this is more common, however, doctors know what to look for, and are often much more likely to treat the infection as a parasitic nematode from the beginning.

Photo Credit: stanford.edu

Look at that lovely y-shaped lateral chord! It's one of the best ways to recognize an Anisakid nematode larva.