Rev: 10/19/2026
Chromadorea
Chromadoria
Rhabditida
Spirurina
Ascaridoidea
Anisakidae
Contracaecum Railliet & Henry, 1912
Although sometimes classified in the family Heterocheilidae, molecular analyses by Nadler et al (2005) demonstrated strong support for the monophyly of Contracaecum, Phocasacaris, Porrocaecum, Pseudoterranova and Anisakis in the family Anisakidae. Contracaecum is the most speciose genus in the Anisakidae.
Adult Contracaecum spp. are parasites of piscivorous birds and marine mammals, including both cetaceans and pinnipeds (Shamsi et al., 2009).
Synonyms:
Cerascaris Cobb, 1929
Kathleena Leiper & Atkinson, 1914
Medium-large sized (some 1-8 cm long), Species of Contracaecum have been defined on the basis of distribution of caudal papillae in the male and numerous other structural features of the adult worms. Due to intraspecific variation, morphometric identiification of species is sufficiently difficult that at least 30 adults of each sex at least should be studied, by light microscopy, to allow identification (Fagerholm and Overstreet, 2008). Caudal features generally differentiate species from seals from those that occur in birds. However, morphological data suggest that host-switching might have occurred from birds to seals in some species.
The genus Contracaecum includes approximately 140 species, which are distributed globally in marine environments (Shamsi et al., 2009).
Food Sources and Feeding strategies for the genus Contracaecum
Parasites of fish, fish-eating birds and marine mammals.
Adult Contracaecum spp. are parasites of fish-eating birds and marine mammals, including both cetaceans and pinnipeds. Typically they are parasites of the proventriculus, gizzard, and intestines of birds, seals, and dolphins.
Usually, the second larval stage of Contracaecum spp. hatches from eggs released in the feces from infected definitve hosts. Copepods act as intermediate hosts, and small fish harboring third stage larvae act as vertebrate intermediate or paratenic hosts
Humans are accidental hosts due to ingestion of raw or undercooked fish containing the third infective-stage larvae. Human anisakiasis patients suffer from abdominal pain, nausea, vomiting, and/or diarrhea (Dorny et al., 2009).
The following detailed descriptions and lifecycles of nematodes associated with Anisakiasis are provided courtesy of CDC, the Centers for Disease Control and Prevention
Causal Agents
Anisakiasis is caused by the ingestion of larvae of several species of ascaridoid nematodes (roundworms), which are sometimes called herringworm, codworm, sealworm, in undercooked marine fish. Known human-infecting anisakid species include members of the Anisakis simplex complex [A. simplex sensu stricto, A. pegreffii, A. berlandi (=A. simplex C)], the Pseudoterranova decipiens complex (P. decipiens sensu stricto, P. azarasi, P. cattani, and others), and the Contracecum osculatum complex. Recent genetic studies have revealed high diversity within these anisakid groups, suggesting additional cryptic species are likely represented in zoonotic infections.
Adult stages of anisakid nematodes reside in the stomach of marine mammals, where they are embedded in the mucosa in clusters. Unembryonated eggs produced by adult females are passed in the feces of marine mammals . The eggs become embryonated in water, undergoing two developmental molts , and hatch from the eggs as free-swimming ensheathed third-stage (L3) larvae . These free-swimming larvae are then ingested by crustaceans . The ingested larvae grow within the crustacean hemocoel, and become infective to fish and cephalopod paratenic hosts. After preying upon infected crustaceans, the digested L3 larvae migrate from the paratenic host intestine into the abdominal cavity, and eventually to the tissues of the mesenteries and skeletal muscle. Through predation, tissue-stage L3 larvae can be transmitted among paratenic hosts . Fish and squid maintain L3 larvae that are infective to humans and marine mammals .
When fish or squid containing third-stage larvae are ingested by definitive host marine mammals, the larvae molt twice and develop into adult worms . After ingestion by humans, the anisakid larvae penetrate the gastric and intestinal mucosa, causing the symptoms of anisakiasis .
Unmanageable infections in wild birds result from biological and environmental conditions that concentrate birds and intermediate hosts together.
In domestic situations, intermediate and paratenic hosts can be eliminated or reduced. Birds can be medicated, if necessary, for treatment of breeding stock or valuable individuals.
Albendazole and fenbendazole were effective against Contracaecum multipapillatum in the Brown Pelican while piperazine dihydrochloride, clorsulon, and Curatrem were not. Recent studies should be reviewed in this area with regards to both efficacy and safety.
Cooking-infected products destined for consumption by humans or other animals will kill all stages of Contracaecum and Porrocaecum,
The US Department of Agriculture recommends freezing and storing at -20 C or below for 7 days. Heating to 63 C for 17 min will also kill all nematodes in infected tissue, as well as bacteria.
Control practices for some anisakid infections under normal conditions in the wild can be cost-prohibitive, not practical, or totally unnecessary.
For Porrocaecum or Contracaecum, control strategies should first consider eliminating or reducing access to the intermediate hosts.
Ref: Fagerholm H-P. and Overstreet, R.M. 2008
Dorny, P., Praet, N., Deckers, N. and Gabriel, S. 2009. Emerging food-borne parasites. Veterinary Parasitology 163:196-206.
Fagerholm H-P. and Overstreet, R.M. 2008. Ascaridoid Nematodes: Contracaecum, Porrocaecum, and Baylisascaris, Chapter 24 in Atkinson, C.T., Thomas, N.J. and Hunter, D.B. (eds) Parasitic Diseases of Wild Birds. John Wiley & Sons, Inc. ISBN: 978-0-813-82081-1
Klimpel, S. and Palm, H. W. 2011. Anisakid nematode (Ascaridoidea) life cycles and distribution: Increasing zoonotic potential in the time of climate change? In Mehlhorn, H. (Ed.), Progress in parasitology. Parasitology research monographs, Vol. 2 Springer, Berlin, pp. 201-222.
Nadler, S.A., D'Amelio, S., Dailey, M.D. Paggi, L., Siu, S., Sakinari, J. A. Molecular phylogenetics abnd diagnosis of Anisakis, Pseudoterranova, and Contracaecum from Nothern Pacific marine mammals. J. Parasitol. 91:1413-1429.
Shamsi, S., Norman, R., Gasser, R., Beveridge, I. 2009. Redescription and genetic characterization of selected Contracaecum spp. (Nematoda: Anisakidae) from various hosts in Australia. Parasitology Research 104:1507-1525.