Rev: 11/07/2023
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, 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
The genus Contracaecum includes approximately 140 species, which are distributed globally in marine environments (Shamsi et al., 2009).
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. .Usually, the second larval stage hatches from eggs released in the feces from infected 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 associased 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 .
Dorny, P., Praet, N., Deckers, N. and Gabriel, S. 2009. Emerging food-borne parasites. Veterinary Parasitology 163:196-206.
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.