Pseudoterranova spp

From Fish
Anisakis simplex (left) and Pseudoterranova dicipiens (right) both in cod (photos courtesy of Dr. Stig Mellergaard).
A boring tooth (arrow) at the anterior end of Pseudoterranova.

Pseudoterranova spp are an Anasakid nematode parasite that affects marine fish and squid.

The parasite has been reported in Japanese Spanish mackerel (Scomberomorus niphonius), chum salmon (Oncorhynchus keta), Pacific cod (Gadus macrocephalus), Alaska pollack (Theragra chalcogramma), Okhotsk atka mackerel (Pleurogrammus azonus), Japanese common squid (Todarodes pacificus), and many other marine fishes.

This parasite, similar to Anasakis spp, infects the body cavity, visceral organs, and muscles[1].

Life cycle

The definitive host is mainly Pinnipeds (seal, sealion, etc.). Released larva hatched from an egg is ingested by crustacean, e. g. euphausiid. Fishes are infected by eating such krill. The parasite, red-brown in color, has the boring tooth at the anterior end and the mucro (tail spine) at the posterior end. In a limited sense (sensu strict), ‘Pseudoterranova decipience’ means only the one species P. decipience, meanwhile, in the broad sense (sensu lato), P. decipience includes several species, which are genetically different each other[2].

Clinical signs

No external sign is observed. A filiform worm (1-4 cm in length) is found in the body cavity, liver and stomach wall. The worm is not coiled in the fish hosts.

The effects of infection to the host are possibly low. The live parasite, a causative agent of anisakiasis, penetrates into the wall of gut and causes the acute gastroenteritis, viz. violent abdominal pain, nausea and vomiting. Therefore, be careful when the host fish is consumed raw. Heating or freezing to -20 C for 24 hours are effective for killing the parasite[3].

Diagnosis

Diagnosis requires comparing to Anisakis. Pseudoterranova is larger and reddish in color[4]. The distinct morphological characteristic is the presence of caecum in the latter species. Thhe intestine is brownish yellow in color and the tail is conical and tapers from around the anus. At present, several disgnostic methods such as PCR and restriction fragment length polymorphism (RFLP) mapping have been developed[5].

References

  1. Nadler, S. A., et al (2005) Molecular phylogenetics and diagnosis of Anisakis, Pseudoterranova, and Contracaecum from Northern Pacific marine mammals. J Parasitol 91:1413-1429
  2. Paggi, L., S. et al (2000) Pseudoterranova decipiens species A and B (Nematoda, Ascaridoidae): nomenclatural designation, morphological diagnostic characters and genetic markers. Syst Parasitol 45:185-197
  3. Zhu, X. Q., et al (2002) SSCP-based identification of members within the Pseudoterramova decipiens complex (Nematoda: Ascaridoidea: Anisakidae) using genetic markers in the internal transcribed spacers of ribosomal DNA. Parasitology 124:615-623
  4. Ishikura, H. (1999) Anisakiasis (2) Clinical pathology and epidemiology. Progress of medical parasitology in Japan. Meguro Parasitological Museum 7:439-464
  5. Kijewska, A., J. Rokicki, J. Sitko and C. Wegrzyn (2002) Ascaridoidea: a simple DNA assay for identification of 11 species infecting marine and freshwater fish, mammals, and fish-eating birds. Exp Parasiol 101:35-39