Answer to Case 689

 Answer to the Parasite Case of the Week 689:  Anisakid, most consistent with an Anisakis species.

Hopefully you all had a change to look at the whole slide image HERE. From its location in the small intestine, deep in the submucosa, one can envision how it may have extended through the wall of the intestine and caused a perforation. 

Dr. Luca Fanasca noted that "we can clearly see features consistent with an anisakid infection: multilayered cuticle (from a portion which seems detached, in the upper part), polymyarian muscle cells, the beautiful Y shaped lateral chords and the banana-shaped excretory cell. From the quite slender appearance of the lateral cords I think we could suppose this is actually an Anisakis sp., but a definitive identification would require the observation of other characteristics like the caecum position and shape, or molecular diagnostics strategies." 

Below are some of the key features of nematodes, and anisakids in particular: 

Features of all nematodes:

1. Acellular outer cuticle (may be adorned projections in some nematodes (e.g., the lateral alae of Enterobius vermicularis, and the cuticular bosses of Loa loa)
2. Underlying musculature. The musculature is either flattened (platymyarian) or tall (coelomyarian). The musculature is further categorized by the number of muscle cells: meromyairan (2 to 5 rows) or polymyarian (large number of rows in each sector)
3. Lateral chords 
4. Fully-developed intestinal tract
5. Separate sexes (males and females)

Features of anisakids in particular:

1. L3 larva embedded in the wall of the stomach or intestine (or in the peritoneal cavity)
2. Thick unadorned cuticule
3. Tall coelomyarian musculature (m)
4. Splayed, Y-shaped lateral cords (arrow heads). The slender appearance of lateral cords are consistent with Anisakis species.
5. Prominent esophagus (black asterisk)
6. Banana-shaped excretory cell (white asterisk)