Marine Mammal Parasite of the Month – Answer January 2012

Answer month 1: Anisakis species

These are roundworms or nematodes.  The first clue was obscured in the original post (didn’t think I was going to make this too easy did you?) and required you to look at the oral opening and the three lips (covered in this case by the capsule). This and the marine mammal host place them in the family Anisakidae.

Here is a close up of the lips from another specimen (in this case a harbor seal, likely a different genus), each red arrow points to a “lip”.

The capsule (a molt) and the point on the terminal end (a mucron), combined with the  lack of spicules or eggs, identifies this as a larval form (L3).

This is a classic group of marine nematodes where the adults inhabit marine mammals and the larva use a huge number of different intermediate and transport hosts.  The Anisakidae are further classified into their respective genus by the morphology of their esophagus, ventriculus and presence or lack of an intestinal caecum (see chart).  In this case, the simple ventriculus identifies the genus Anisakis.

The species identification requires the adult (or L5) males which were not observed in this case.

Many reviews of the Genus Anisakis (Dujardin, 1845) have been published; for the truly geeky see the following:  Davey 1971; Abollo and Pascual 2002.

Known species of Anisakis:
A. physeteris (Baylis, 1923)
A. typica (Diesing, 1860)
A. simplex (Rudolphi, 1809) senso lato complex (with 13 synonyms)
A. simplex s.s.
A. pegreffi (Campana, Rouget & Bioca, 1954)
A. simplex (Nascetti et al., 1986)
A. ziphidarum (Paggi, et al., 1998)
A. brevispiculata (Dollfus, 1966)

Of these,  A. simplex , A. brevispiculata, and A. physeteris have all been found in Kogia.

The larval forms are zoonotic and can be pathogenic to the host, particularly in large numbers or when they cause ulceration.  The worm in the blowhole was likely aspirated as a terminal event, as the worms are inhabitants of the stomach. The genus is intensely studied as the larval worms are human health hazards, typically encountered by eating improperly cooked fish and resulting in the unpleasant disease called Anisakiasis.  Recent genetic studies may hold the key to correct identification of larval forms.

The best way to handle them (besides “with gloves” which I also accepted) is to wash them by shaking them in a jar with 0.9% saline to remove blood and mucous, then fix them in near boiling saline for 5 seconds to straighten the worms, then move them to a vial with 70% ethanol and add a few drops of glycerin.  They can also be fixed in glacial acetic acid for a few hours and stored in 70% ethanol with a few drops of glycerin added.