HELMINTHS Acanthocephalans (Spiny-Headed Worms)

I. Causative Agent and Disease An egg will hatch in the intermediate Acanthocephalans are endoparasitic host releasing an acanthor that penetrates worms characterized by a retractable the gut and develops into an acanthella/ proboscis armed with rows of hooks used cystocanth. The life cycle is complete to attach to the intestines of fish. Many when a fish eats a parasitized microcrus- genera have been described as adults in tacean and the adult worm develops in the intestines of fish while some larval the alimentary tract of the fish host. In forms have also been identified in the some cases, fish are the second interme- viscera. Genera commonly found in diate host as well as the final host. Alaskan fishes are Neoechinorhynchus, Acanthocephalus and Corynosoma. Gut V. Diagnosis infestation by numerous acanthocepha- Diagnosis is made by the visual de- lans can cause fibrotic nodules on the tection of adult acanthocephalans in the surface of the intestine. The intestine intestine or invasive larvae in the body may become inflamed with the destruc- cavity of a parasitized fish. The shape of tion of intestinal villi and resulting the proboscis, the arrangement and the necrotic and degenerative changes in number of proboscis hooks are important mucosal epithelium. Intestinal absorptive characteristics used to definitively iden- efficiency may be compromised leading tify the of acanthocephalan. PCR to decreased growth and emaciation. has been useful in confirming species Acanthocephalans occasionally perfo- that has resulted in changing . rate the intestinal wall which can lead to peritonitis and death of the host. VI. Prognosis for Host The principal effects on the final host II. Host Species can include mechanical damage to the Acanthocephalans have been found intestinal wall and emaciation. Signifi- in both marine and freshwater fishes cant fish mortality or emaciation due to worldwide. infestation by acanthocephalans are rare unless the worms are present in large III. Clinical Signs numbers. Parasitized fish may be emaciated with inflamed intestinal tracts and tissue VII. Human Health Signifcance necrosis in areas where worms are at- There are no human health concerns tached to the intestinal wall. associated with these parasites.

IV. Transmission Acanthocephalans require a ver- tebrate as a definitive host and arthropods as an intermediate host. Fish usually are the final host for aquatic acanthocephalans and microcrustaceans (amphipod, copepod, isopod or ostracod) are generally the intermediate host. Inter- mediate hosts are infected by eating eggs eliminated in the feces of parasitized fish.

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Acanthocephalan worm of the Pomphorhynchus.

Pomphorhynchus: a higher magnifcation of the spiny head (proboscis) showing numerous hooks, X 200.

Highly armed proboscis of Echinorhynchus.

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