Bothriocephalus acheilognathi

Asian tapeworm
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Cestoda
Order:	Pseudophyllidea
Family:	Bothriocephalidae
Genus:	Bothriocephalus
Species:	B. acheilognathi
Binomial name
	Bothriocephalus acheilognathi; Yamaguti, 1934
Synonyms
	Bothriocephalus opsariichthydis Yamaguti, 1934; Bothriocephalus gowkongensisYeh, 1955; ...and see text

Last updated December 17, 2023

Bothriocephalus acheilognathi, also known as the Asian tapeworm, is a freshwater fish parasite that originated from China and Eastern Russia. It is a generalized parasite that affects a wide variety of fish hosts, particularly cyprinids, contributing to its overall success.^[1]

Description

B. acheilognathi has a fleshy scolex (head region) with an undeveloped terminal disc and two long attachment grooves called bothria positioned dorsoventrally. The scolex is distinctively shaped like an inverted heart or an arrowhead. Its ribbon-like body consists of flattened segments called proglottids. It typically grows to a length of 3.5 to 8 cm (1.4 to 3.1 in) with widths of up to 4 mm (0.16 in), but exceedingly large specimens reaching 60 to 100 cm (2.0 to 3.3 ft) have been recorded.^[2] They are remarkable in their ability to adapt their sizes depending on the size of their hosts.^[3]

Taxonomy

Bothriocephalus acheilognathi has more than twenty known synonyms.^[2] It was originally described as three species, all of them from non-native populations. In 1934, the Japanese helminthologist Satyu Yamaguti first described specimens from wild fish recovered from Ogura Lake, Japan. He named them as two different species - Bothriocephalus acheilognathi and Bothriocephalus opsariichthydis. In 1955, the Chinese helminthologist Liang-Sheng Yeh described more specimens recovered from grass carp ( Ctenopharyngodon idella ) in South China as Bothriocephalus gowkongensis. These species were later recognized as synonyms by later authors, and Yamaguti's original name for the species was retained by the rules of precedence.^[3]^[4]

Distribution and habitat

The natural host of Bothriocephalus acheilognathi is the grass carp which is native to the Amur River in China and eastern Russia. But it has become widespread throughout the world by means of introductions of the grass carp. Even the type specimens were not native. It is now known to exist in Europe, Australia, Mexico, Panama, Honduras,^[5] the United States, Canada, and Puerto Rico. It can infect species of fish that belong to the families Cyprinidae, Poecilidae, Cichlidae and Centrarchidae.^[4]^[6] In Australia, it infects fish in the Family Eleotridae, and likely others.

Pathology

The parasite attaches near the anterior portion of the intestine, just posterior to the bile duct. An accumulation of tapeworms in this area leads to digestive tract blockage that distends the intestinal wall leading to perforation. When attached, B. acheilognathi envelopes parts of the intestines and induces an inflammatory response. The inflammation can lead to hemorrhage and necrosis. Clinical signs also include, weight loss, anemia, and mortality (especially in young fishes).^[3] Infections can be detected by the presence of eggs or body parts in feces, and by the presence of the tapeworm in the gut of the fish.

Life cycle

The life cycle of B. acheilognathi involves a definitive host, a fish, and an intermediate host, a copepod. The adult tapeworm is hermaphroditic; each proglottid has a complete set of both male and female reproductive organs and produces eggs via self-fertilization. The tapeworm is sensitive to temperature, in addition the species is thermophilic; lower temperatures interfere and delay development and completion of the life cycle. The eggs are released into the water through the fish fecal material, where they hatch into free-swimming hexacanth (six-hooked) larvae. Between 1 and 28 days, the eggs will hatch according to the water temperature range it is in. Eggs that hatch within 1–5 days occur at temperatures between 28 and 30 °C and eggs that hatch within 10–28 days occur at temperatures between 14 and 15 °C.^[4]^[6]

When the free-swimming larvae, called coracidia, are eaten by copepods (intermediate host), it penetrates into the gut wall, travels to the coelom, and develops into a second larval stage called a procercoid (infective form) all within 6–10 days. Once the infected copepods are eaten by the fish hosts, the procercoid rapidly transform into the plerocercoid stage and attaches to the intestinal gut wall, where it develops into the adult parasite over the course of 21–23 days.^[4]^[6]

Ecological impact

Studies have shown that B. acheilognathi decreases the size of fish worldwide causing great economic loss in hatcheries and fish farms. The Asian tapeworm was introduced globally via grass carp. Infestation is intermittent and follows a clear seasonal pattern with peak incidence in the summer. There are multiple chemotherapeutic solutions to fight infection. Tinostat, Yomesan, Droncit are examples of drugs (when mixed in fish food with oil) that are effective in relieving infection. Eliminating an infestation can be amplified by control of copepods in water.^[3]^[4]^[6]

In North America, introduced B. acheilognathi are also known to infect threatened native species like humpback chub ( Gila cypha ), Mojave tui chub ( Siphateles bicolor mohavensis ), Virgin roundtail chub ( Gila robusta seminuda ), woundfin minnow ( Plagopterus argentissimus ),^[4] Profundulus portillorum ^[5] and the crucian carp ( Carassius carassius ).^[7] The discovery of the tapeworm's substantial infections within the crucian carp population in the UK is of particular concern because there have not been any known natural tapeworm parasites of these crucian carp. A plausible cause may be that the crucian carp have limited immunological defenses against this parasite.^{[ citation needed ]} In Australia, introduced B. acheilognathi has caused fish kills of Western Carp Gudgeon and is strongly suspected of affecting other Australian freshwater fish species.^[8]

Related Research Articles

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Diphyllobothrium is a genus of tapeworms which can cause diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriasis is D. latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode that infects fish and mammals. D. latum is native to Scandinavia, western Russia, and the Baltics, though it is now also present in North America, especially the Pacific Northwest. In Far East Russia, D. klebanovskii, having Pacific salmon as its second intermediate host, was identified.

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The Caryophyllideans are a group of tapeworms that infect fish and annelids with a simple scolex or "head." Worms in this order only have one proglottid, which is believed to be the primitive condition for tapeworms. They are generally less than 10 centimetres long. Caryophillideans represent a unique type of tapeworm, such that they possess a monzoic, unsegmented, body, with only a single set of reproductive organs.

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<i>Hymenolepis nana</i> Species of flatworm

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References

↑ V. Diaz-Castaneda; A. Carabez-Trejo; R. Lamothe-Argumedo (1995). "Ultrastructure of the pseudophyllidean cestode Bothriocephalus acheilognathi, parasite of freshwater fish of commercial importance" (PDF). Anales del Instituto de Biologia, Universidad Nacional Autonoma de Mexico, Serie Zoologia. 66 (1): 1–16.
1 2 Tomáš Scholz; Roman Kuchta & Chris Williams (2012). "Bothriocephalus acheilognathi". In Patrick T. K. Woo & Kurt Buchmann (eds.). Fish Parasites:Pathobiology and Protection. CABI. p. 282–297. ISBN 978-1-84593-806-2.
1 2 3 4 Ilan Paperna (1996). Parasites, infections and diseases of fishes in Africa: An update. CIFA Technical Paper. Food and Agriculture Organization of the United Nations. pp. 155–156. ISBN 92-5-103772-8.
1 2 3 4 5 6 Mary Hejna (August 19, 2009). "Bothriocephalus acheilognathi ". USGS Nonindigenous Aquatic Species Database. Retrieved March 6, 2012.
1 2 Salgado-Maldonado, Guillermo; Matamoros, Wilfredo A.; Kreiser, Brian R.; Caspeta-Mandujano, Juan Manuel; Mendoza-Franco, Edgar F. (2015). "First record of the invasive Asian fish tapeworm Bothriocephalus acheilognathi in Honduras, Central America". Parasite. 22: 5. doi:10.1051/parasite/2015007. ISSN 1776-1042. PMC 4318484 . PMID 25654444.
1 2 3 4 David J. Marcogliese (2008). "First report of the Asian fish tapeworm in the Great Lakes". Journal of Great Lakes Research. 34 (3): 566–569. doi:10.3394/0380-1330(2008)34[566:FROTAF]2.0.CO;2. S2CID 83843864.
↑ Ash Girdler & Ian Wellby (2010). Fisheries Management: A Manual for Still-water Coarse Fisheries. John Wiley and Sons. p. 49. ISBN 978-1-4051-3332-6.
↑ Lintermans M. (2007). Fishes of the Murray-Darling Basin—An Introductory Guide. Murray-Darling Basin Commission, Canberra. pp. 102–103.