A cystacanth is the infective juvenile or larval stage of an acanthocephalan, a member of the group of parasitic worms commonly known as thorny-headed worms. It follows the acanthella stage and is the stage normally transmitted to a vertebrate definitive host when that host eats an infected intermediate host or, in some life cycles, a paratenic host.[1][2]
Although the name refers to cyst-shaped larvae, it is not limited to rounded forms. Some acanthocephalan infective larvae are elongated and resemble immature adults with an invaginated anterior region, so the term has been described as established but partly imprecise.[1]
Life cycle
editAcanthocephalans have indirect life cycles involving an invertebrate intermediate host and a vertebrate definitive host. Eggs passed by the definitive host contain an acanthor. After the egg is eaten by a suitable arthropod intermediate host, the acanthor hatches, penetrates host tissues, and develops into an acanthella. The final larval stage in the intermediate host is the cystacanth, which is infective to the definitive host.[3][4]
In a definitive host, the cystacanth is liberated from its cyst, everts or partly everts its hooked proboscis, attaches to the intestinal wall, and develops into an adult worm.[2] Development may also involve paratenic hosts, which carry viable juvenile parasites without allowing them to mature. Marine fish, for example, can serve as paratenic hosts for cystacanths of genera such as Bolbosoma and Corynosoma.[5][6]
Morphology
editCystacanths are broadly similar to adult acanthocephalans, but their reproductive organs and other internal structures are not fully developed. Mature cystacanths are commonly recognized by a completely inverted proboscis held in the proboscis receptacle until transmission to the definitive host.[2] In live cystacanths of Corynosoma, researchers have described cycles of proboscis evagination and invagination and associated body movements involved in attachment.[7]
The cyst enclosing an acanthocephalan larva varies among species. A 2025 review of cyst formation in intermediate hosts reported that most described cysts are bilayered, with a relatively thick vesicular outer layer and a thinner amorphous layer underneath, while also noting several different mechanisms of cyst formation.[8]
Identification
editCystacanths are often identified by external morphology, including body shape, trunk spination, and the number and arrangement of hooks on the proboscis.[2] Identification can be difficult when the adult stage is unknown or when larval morphology is insufficiently distinctive. In Bolbosoma, morphology-based identification at the cystacanth stage has been described as challenging, and DNA barcoding has been used together with classical morphology to identify larvae recovered from marine fish.[9]
Transmission ecology
editBecause cystacanths are transmitted trophically, changes in intermediate-host behavior can affect the probability that the parasite reaches its definitive host. Experimental work on Pomphorhynchus laevis found that host behavioral alteration appeared only after the parasite reached the cystacanth stage and that older cystacanths induced stronger manipulation.[10] Later work on Pomphorhynchus tereticollis and the amphipod Gammarus fossarum also found that behavioral effects depended on parasite developmental stage.[11]
Medical and veterinary relevance
editHuman acanthocephaliasis is rare. In human-associated life cycles summarized by the Centers for Disease Control and Prevention, infection occurs when a person ingests an intermediate host containing infective cystacanths; in humans, the worms seldom reach full maturity or produce eggs.[4] Fish-borne cystacanths of Bolbosoma and Corynosoma have also been discussed as potential human pathogens when live larvae are consumed in raw or insufficiently treated fish products.[5]
See also
editReferences
edit- 1 2 Mehlhorn, Heinz, ed. (2008). "Cystacanth". Encyclopedia of Parasitology. Berlin, Heidelberg: Springer. pp. 314–316. doi:10.1007/978-3-540-48996-2_791. ISBN 978-3-540-48996-2.
- 1 2 3 4 Gardner, Scott L.; Gardner, Sue Ann, eds. (2024). "Chapter 12: Introduction to the Acanthocephala". Concepts in Animal Parasitology. Lincoln, Nebraska: Zea Books. doi:10.32873/unl.dc.ciap070. Retrieved May 22, 2026.
- ↑ Schmidt, Gerald D.; Nickol, Brent B. (1985). "Development and Life Cycles". In Crompton, D. W. T.; Nickol, Brent B. (eds.). Biology of the Acanthocephala. Cambridge University Press. pp. 273–305. ISBN 0521246741. Retrieved May 22, 2026.
- 1 2 "CDC - DPDx - Acanthocephaliasis". DPDx. Centers for Disease Control and Prevention. April 11, 2019. Retrieved May 22, 2026.
- 1 2 Buchmann, Kurt; Karami, A. M. (2024). "Fish Acanthocephalans as Potential Human Pathogens". Current Clinical Microbiology Reports. 11 (2): 99–106. doi:10.1007/s40588-024-00226-9.
- ↑ García-Varela, Martín; Sereno-Uribe, Ana L.; Solórzano-García, Brenda; Pérez-Ponce de León, Gerardo (2024). "The white grunt, Haemulon plumierii (Lacepède, 1801) as paratenic and definitive host of two acanthocephalan species, with the description of a new species of Dollfusentis (Palaeacanthocephala: Leptohynchoididae) from the Yucatán Peninsula, Mexico". Journal of Helminthology. 98 e31. doi:10.1017/S0022149X24000105. PMID 38584424.
- ↑ Aznar, Francisco Javier; Hernández-Orts, Jesús Servando; Raga, Juan Antonio (2018). "Morphology, performance and attachment function in Corynosoma spp. (Acanthocephala)". Parasites & Vectors. 11 633. doi:10.1186/s13071-018-3165-1. PMC 6293589. PMID 30545426.
- ↑ Nikishin, V. P.; Davydenko, T. V.; Skorobrekhova, E. M. (2025). "Morphological variety and mechanisms of formation of acanthocephalan cysts in intermediate host". Journal of Helminthology. 99 e49. doi:10.1017/S0022149X25000306. PMID 40159910.
- ↑ Kita, Yuki; Waki, Tsukasa; Kajihara, Hiroshi (2024). "Cystacanths of Bolbosoma (Acanthocephala: Polymorphidae) from Six Species of Marine Fish around Japan, with Molecular Information". Species Diversity. 29 (2): 317–325. doi:10.12782/specdiv.29.317.
- ↑ Franceschi, Nathalie; Bauer, Alexandre; Bollache, Loïc; Rigaud, Thierry (2008). "The effects of parasite age and intensity on variability in acanthocephalan-induced behavioural manipulation". International Journal for Parasitology. 38 (10): 1161–1170. doi:10.1016/j.ijpara.2008.01.003. PMID 18314127.
- ↑ Cozzarolo, Camille-Sophie; Perrot-Minnot, Marie-Jeanne (2022). "Infection with an acanthocephalan helminth reduces anxiety-like behaviour in crustacean host". Scientific Reports. 12 (1) 21649. Bibcode:2022NatSR..1221649C. doi:10.1038/s41598-022-25484-9. PMC 9755125. PMID 36522391.