Cestoda

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Cestoda
Temporal range: 270 –0  Ma [1]
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Taenia saginata adult 5260 lores.jpg
Taenia saginata
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Platyhelminthes
Class:Cestoda
Subgroups

See text.

Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species - and the best-known - are those in the subclass Eucestoda; they are ribbonlike worms as adults, known as tapeworms. Their bodies consist of many similar units, known as proglottids, which are essentially packages of eggs which are regularly shed into the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish parasites.

In biological classification, class is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order.

Parasitic worm A commonly used term to describe certain parasitic worms with some similarities, many of which are intestinal worms

Parasitic worms, also known as helminths, are large macroparasites, which as adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schistosomes reside in blood vessels.

Flatworm Phylum of animals, flatworms

The flatworms, flat worms, Platyhelminthes, Plathelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Unlike other bilaterians, they are acoelomates, and have no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion. The digestive cavity has only one opening for both ingestion and egestion ; as a result, the food cannot be processed continuously.

Contents

All cestodes are parasitic; many have complex life histories, including a stage in a definitive (main) host in which the adults grow and reproduce, often for years, and one or two intermediate stages in which the larvae develop in other hosts. Typically the adults live in the digestive tracts of vertebrates, while the larvae often live in the bodies of other animals, either vertebrates or invertebrates. For example, Diphyllobothrium has at least two intermediate hosts, a crustacean and then one or more freshwater fish; its definitive host is a mammal. Some cestodes are host-specific, while others are parasites of a wide variety of hosts. Some six thousand species have been described; probably all vertebrates can host at least one species.

Parasitism Interaction between two organisms living together in more or less intimate association in a relationship in which association is disadvantageous or destructive to one of the organisms

In evolutionary biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Parasites include protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes. There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism, trophically transmitted parasitism, vector-transmitted parasitism, parasitoidism, and micropredation.

Life history theory is an analytical framework designed to study the diversity of life history strategies used by different organisms throughout the world, as well as the causes and results of the variation in their life cycles. It is a theory of biological evolution that seeks to explain aspects of organisms' anatomy and behavior by reference to the way that their life histories—including their reproductive development and behaviors, life span and post-reproductive behavior—have been shaped by natural selection. A life history strategy is the "age- and stage-specific patterns" and timing of events that make up an organism's life, such as birth, weaning, maturation, death, etc. These events, notably juvenile development, age of sexual maturity, first reproduction, number of offspring and level of parental investment, senescence and death, depend on the physical and ecological environment of the organism.

Larva juvenile form of distinct animals before metamorphosis

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.

The adult tapeworm has a scolex, or head, a short neck, and a strobila, or segmented body formed of proglottids. Tapeworms anchor themselves to the inside of the intestine of their host using their scolex, which typically has hooks, suckers, or both. They have no mouth, but absorb nutrients directly from the host's gut. The neck continually produces proglottids, each one containing a reproductive tract; mature proglottids are full of eggs, and fall off to leave the host, either passively in the feces or actively moving. All tapeworms are hermaphrodites, with each individual having both male and female reproductive organs.

Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork ( Taenia solium ), beef ( T. saginata ), and fish (Diphyllobothrium), or if they live in, or eat food prepared in, conditions of poor hygiene ( Hymenolepis or Echinococcus species). The unproven concept of using tapeworms as a slimming aid has been touted since around 1900.

Pork meat from a pig

Pork is the culinary name for meat from a domestic pig. It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BC.

<i>Taenia solium</i> species of Cestoda

Taenia solium is the so-called pork tapeworm belonging to cyclophyllid cestodes in the family Taeniidae. It is an intestinal mainly zoonotic parasite found throughout the world, and is most prevalent in countries where pork is eaten, and in its more dangerous secondary form wherever faecally contaminated water is drunk, having been infected by primary, human hosts. The adult worm has as its main host humans and has a flat, ribbon-like body, which is white and measures 2 to 3 metres long or more. Its tiny long attachment, the scolex, contains duodenum wall-suckers and a rostellum as organs of attachment. The main body, the strobila, consists of a chain of segments known as proglottids. Each proglottid is little more than a self-sustainable, very lightly ingestive, reproductive unit; hence, the tapeworm is a hermaphrodite. It completes its life cycle in humans as the definitive host and often pigs as intermediate host. It may be transmitted to pigs through human feces contaminating their fodder, and back to humans wherever primary hosts through uncooked or undercooked pork bearing small cysts. Pigs ingest embryonated eggs called morula, which develop into larvae, the oncospheres, and ultimately into infective larvae, cysticerci. A cysticercus grows into an adult worm in human small intestines. Primary hosts often present no pathological symptoms. Secondary human hosts, infected by faecally contaminated water or matter by definition develop its complication cysticercosis, the most harmful and chronic form of which is neurocysticercosis. Primary hosts can be easily treated with oral medicines. Treatment of secondary hosts is more difficult but possible.

<i>Taenia saginata</i> species of Cestoda

Taenia saginata, commonly known as the beef tapeworm, is a zoonotic tapeworm belonging to the order Cyclophyllidea and genus Taenia. It is an intestinal parasite in humans causing taeniasis and cysticercosis in cattle. Cattle are the intermediate hosts, where larval development occurs, while humans are definitive hosts harbouring the adult worms. It is found globally and most prevalently where cattle are raised and beef is consumed. It is relatively common in Africa, Europe, Southeast Asia, South Asia, and Latin America. Humans are generally infected as a result of eating raw or undercooked beef which contains the infective larvae, called cysticerci. As hermaphrodites, each body segment called proglottid has complete sets of both male and female reproductive systems. Thus, reproduction is by self-fertilisation. From humans, embryonated eggs, called oncospheres, are released with faeces and are transmitted to cattle through contaminated fodder. Oncospheres develop inside muscle, liver, and lungs of cattle into infective cysticerci.

Diversity and habitat

All 6000 species of Cestoda are parasites, mainly intestinal; their definitive hosts are vertebrates, both terrestrial and marine, while their intermediate hosts include insects, crustaceans, molluscs, and annelids as well as other vertebrates. [2]

T. saginata, the beef tapeworm, can grow up to 20 m (65 ft); the largest species, the whale tapeworm Tetragonoporus calyptocephalus , can grow to over 30 m (100 ft). [3] [4] Species with small hosts tend to be small. For example, vole and lemming tapeworms are only 13–240 mm (0.5–9.4 in) in length, and those parasitizing shrews only 0.8–60 mm (0.03–2.36 in). [5]

Tetragonoporus is a genus of cestodes in the order Pseudophyllidea. It is a monotypic genus, and the only species is Tetragonoporus calyptocephalus, previously known as Polygonoporus giganticus. This tapeworm is a gut parasite of whales.

Arvicolinae subfamily of rodents

The Arvicolinae are a subfamily of rodents that includes the voles, lemmings, and muskrats. They are most closely related to the other subfamilies in the Cricetidae. Some authorities place the subfamily Arvicolinae in the family Muridae along with all other members of the superfamily Muroidea. Some refer to the subfamily as the Microtinae or rank the taxon as a full family, the Arvicolidae.

Shrew Family of mammals

The shrew is a small mole-like mammal classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, or the West Indies shrews, which belong to different families or orders.

Anatomy

Cestodes have no gut or mouth [6] and absorb nutrients from the host's alimentary tract through their specialised neodermal cuticle, or tegument, [7] through which gas exchange also takes place. [2] The tegument also protects the parasite from the host's digestive enzymes [8] and allows it to transfer molecules back to the host. [7]

Tegument is a term in helminthology for the outer body covering of members of the phylum Platyhelminthes. The name is derived from a Latin word tegumentum or tegere, meaning "to cover". It is characteristic of flatworms including the broad groups of tapeworms and flukes. Once considered to be a non-living component, it is now known to be a dynamic cellular structure. In fact it is a living structure consisting of proteins, lipids, carbohydrates and RNA. It forms the protective layer and the host-parasite interface of the worms, serving both secretory and absorptive functions.

The body form of adult eucestodes is simple, with a scolex, or grasping head, adapted for attachment to the definitive host, a short neck, and a strobila, or segmented [lower-alpha 1] trunk formed of proglottids, which makes up the worm's body. Members of the subclass Cestodaria, the Amphilinidea and Gyrocotylidea, are wormlike but not divided into proglottids. Amphilinids have a muscular proboscis at the front end; Gyrocotylids have a sucker or proboscis which they can pull inside or push outside at the front end, and a holdfast rosette at the posterior end. [6]

The Cestodaria have 10 larval hooks while Eucestoda have 6 larval hooks. [9]

Scolex

Scolex of Taenia solium with hooks and suckers. Taenia solium tapeworm scolex with its four suckers and two rows of hooks 5262 lores.jpg
Scolex of Taenia solium with hooks and suckers.

The scolex, which attaches to the intestine of the definitive host, is often minute in comparison with the proglottids. It is typically a four-sided knob, armed with suckers or hooks or both. [2] In some species, the scolex is dominated by bothria, or "sucking grooves" that function like suction cups. Cyclophyllid cestodes can be identified by the presence of four suckers on their scolices. [10] Other species have ruffled or leaflike scolices, and there may be other structures to aid attachment. [2]

In the larval stage the scolex is similarly shaped and is known as the protoscolex. [11]

Body systems

Circular and longitudinal muscles lie under the neodermis, beneath which further longitudinal, dorso-ventral and transverse muscles surround the central parenchyma. Protonephridial cells drain into the parenchyma. There are four longitudinal collection canals, two dorso-lateral and two ventro-lateral, running along the length of the worm, with a transverse canal linking the ventral ones at the posterior of each segment. When the proglottids begin to detach, these canals open to the exterior through the terminal segment. [2]

The main nerve centre of a cestode is a cerebral ganglion in its scolex. Nerves emanate from the ganglion to supply the general body muscular and sensory endings, with two lateral nerve cords running the length of the strobila. [2] The cirrus and vagina are innervated, and sensory endings around the genital pore are more plentiful than in other areas. Sensory function includes both tactoreception (touch) and chemoreception (smell or taste). [8]

Proglottids

Two proglottids of Taenia solium. This species has 7 to 13 branches of the uterus on each side (above and below in this micrograph). Taenia solium tapeworm proglottids 5261 lores.jpg
Two proglottids of Taenia solium . This species has 7 to 13 branches of the uterus on each side (above and below in this micrograph).

Once anchored to the host's intestinal wall, tapeworms absorb nutrients through their surface as their food flows past them. [12] Cestodes are unable to synthesise lipids, which they use for reproduction, and are therefore entirely dependent on their hosts. [13]

The tapeworm body is composed of a series of segments called proglottids. These are produced from the neck by mitotic growth which is followed by transverse constriction. The segments become larger and more mature as they are displaced backwards by newer segments. [2] Each proglottid contains an independent reproductive tract, and like some other flatworms, cestodes use flame cells (protonephridia), located in the proglottids, for excretion. The sum of the proglottids is called a strobila, which is thin and resembles a strip of tape; from this is derived the common name "tapeworm". Proglottids are continually being produced by the neck region of the scolex, as long as the scolex is attached and alive. [14]

Mature proglottids are essentially bags of eggs, each of which is infective to the proper intermediate host. They are released and leave the host in faeces, or migrate outwards as independent motile proglottids. [14] The number of proglottids forming the tapeworm ranges from three to four thousand. Their layout comes in two forms: craspedote, meaning any given proglottid is overlapped by the previous proglottid, or acraspedote, indicating the proglottids do not overlap. [15]

Reproduction

Cestodes are exclusively hermaphrodites, with both male and female reproductive systems in each body. The reproductive system includes one or more testes, cirri, vas deferens, and seminal vesicles as male organs, and a single lobed or unlobed ovary with the connecting oviduct and uterus as female organs. The common external opening for both male and female reproductive systems is known as the genital pore, which is situated at the surface opening of the cup-shaped atrium. [16] [17] Though they are sexually hermaphroditic and cross-fertilization is the norm, self-fertilization sometimes occurs and makes possible the reproduction of a worm when it is the only individual in its host's gut. [18] During copulation, the cirri of one individual connect with those of the other through the genital pore, and then spermatozoa are exchanged. [2]

Life cycle

Life cycle of the eucestode Taenia: Inset 5 shows the scolex, a disk with hooks on the end. Inset 6 shows the tapeworm's whole body, in which the scolex is the tiny, round tip in the top left corner, and a mature proglottid has just detached. Taenia LifeCycle.gif
Life cycle of the eucestode Taenia : Inset 5 shows the scolex, a disk with hooks on the end. Inset 6 shows the tapeworm's whole body, in which the scolex is the tiny, round tip in the top left corner, and a mature proglottid has just detached.
Life cycle of Diphyllobothrium latum relies on at least three hosts, crustaceans, fish, and humans. Other fish-eating mammals like bears can equally serve as definitive hosts. D latum LifeCycle.png
Life cycle of Diphyllobothrium latum relies on at least three hosts, crustaceans, fish, and humans. Other fish-eating mammals like bears can equally serve as definitive hosts.

Cestodes are parasites of vertebrates, with each species infecting a single definitive host or group of closely related host species. All but amphilinids and gyrocotylids (which burrow through the gut or body wall to reach the coelom [6] ) are intestinal, though some life-cycle stages rest in muscle or other tissues. The definitive host is always a vertebrate but in nearly all cases, one or more intermediate hosts are involved in the lifecycle, typically arthropods or other vertebrates. [2] Infections can be long-lasting; in humans, tapeworm infection may last as much as 30 years. [21] No asexual phases occur in the lifecycle, as they do in other flatworms, but the lifecycle pattern has been a crucial criterion for assessing evolution among Platyhelminthes. [22]

Cestodes produce large numbers of eggs, but each one has a low probability of finding a host. To increase their chances, different species have adopted various strategies of egg release. In the Pseudophyllidea, many eggs are released in the brief period when their aquatic intermediate hosts are abundant (semelparity). In contrast, in the terrestrial Cyclophyllidea, proglottids are released steadily over a period of years, or as long as their host lives (interoparity). Another strategy is to have very long-lived larvae; for example, in Echinococcus, the hydatid larvae can survive for ten years or more in humans and other vertebrate hosts, giving the tapeworm an exceptionally long time window in which to find another host. [23]

Many tapeworms have a two-phase lifecycle with two types of host. The adult Taenia saginata lives in the gut of a primate such as a human, its definitive host. Proglottids leave the body through the anus and fall to the ground, where they may be eaten with grass by a grazing animal such as a cow. This animal then becomes an intermediate host, the oncosphere boring through the gut wall and migrating to another part of the body such as the muscle. Here it encysts, forming a cysticercus. The parasite completes its lifecycle when the intermediate host passes on the parasite to the definitive host, usually when the definitive host eats contaminated parts of the intermediate host, for example a human eating raw or undercooked meat. [2] Another two-phase lifecycle is exhibited by Anoplocephala perfoliata , the definitive host being an equine and the intermediate host an oribatid mite. [24]

Diphyllobothrium exhibits a more complex, three-phase lifecycle. If the eggs are laid in water, they develop into free-swimming oncosphere larvae. After ingestion by a suitable freshwater crustacean such as a copepod, the first intermediate host, they develop into procercoid larvae. When the copepod is eaten by a suitable second intermediate host, typically a minnow or other small freshwater fish, the procercoid larvae migrate into the fish's flesh where they develop into plerocercoid larvae. These are the infective stages for the mammalian definitive host. If the small fish is eaten by a predatory fish, its muscles too can become infected. [2]

Schistocephalus solidus is another three-phase example. The intermediate hosts are copepods and small fish, and the definitive hosts are waterbirds. This species has been used to demonstrate that cross-fertilisation produces a higher infective success rate than self-fertilisation. [25]

Host immunity

Hosts can become immune to infection by a cestode if the lining, the mucosa, of the gut is damaged. This exposes the host's immune system to cestode antigens, enabling the host to mount an antibody defence. Host antibodies can kill or limit cestode infection by damaging their digestive enzymes, which reduces their ability to feed and therefore to grow and to reproduce; by binding to their bodies; and by neutralising toxins that they produce. When cestodes feed passively in the gut, they do not provoke an antibody reaction. [26]

Evolution and phylogeny

Fossil history

Parasite fossils are rare, but recognizable clusters of cestode eggs, some with an operculum (lid) indicating that they had not erupted, one with a developing larva, have been discovered in fossil shark coprolites dating to the Permian, some 270 million years ago. [1] [27]

External

The position of the Cestoda within the Platyhelminthes and other Spiralian phyla based on genomic analysis is shown in the phylogenetic tree. The non-parasitic flatworms, traditionally grouped as the "Turbellaria", are paraphyletic, as the parasitic Neodermata including the Cestoda arose within that grouping. The approximate times when major groups first appeared is shown in millions of years ago. [28] [29]

Platytrochozoa
Rouphozoa

Gastrotricha Polymerurus nodicaudus.jpg

Platyhelminthes

"Turbellaria" Sorocelis reticulosa.jpg

Neodermata
Monogenea

Parasite170078-fig2 Cichlidogyrus philander (Monogenea, Ancyrocephalidae) (main image).png

 fish parasites 
Cestoda

Die Gartenlaube (1857) b 008 1.jpg

 tapeworms and allies 
Trematoda

Botulus microporus.jpg

 flukes 
parasitic
270 mya
Lophotrochozoa

Mollusca Grapevinesnail 01.jpg

Annelida Polychaeta (no).JPG

550 mya
580 mya

Internal

Gyrocotylidea: body flatwormlike, not divided into proglottids Gyrocotyle rugosa.png
Gyrocotylidea: body flatwormlike, not divided into proglottids
Amphilinidea: body wormlike, not divided into proglottids Gigantolina.elongata.in.vivo.png
Amphilinidea: body wormlike, not divided into proglottids
"Tetraphyllidea": elaborate four-leaved scolex Anthobothrium cornucopia.jpg
"Tetraphyllidea": elaborate four-leaved scolex

The evolutionary history of the Cestoda has been studied using ribosomal RNA, mitochondrial and other DNA, and morphological analysis and continues to be revised. "Tetraphyllidea" is seen to be paraphyletic; "Pseudophyllidea" has been broken up into two orders, Bothriocephalidea and Diphyllobothriidea. [30] [31] [32] Hosts, whose phylogeny often mirrors that of the parasites (Fahrenholz's rule), are indicated in italics and parentheses, the life-cycle sequence (where known) shown by arrows as (intermediate host1 [→ intermediate host2] → definitive host). Alternatives, generally for different species within an order, are shown in square brackets. [30] [31] [32]

Cestoda

Gyrocotylidea (fishes)

Amphilinidea (crustaceans → fishes/turtles)

Eucestoda

Spathebothriidea (amphipods → fishes)

Caryophyllidea (annelids → fishes)

Haplobothriidea (freshwater fishes → bowfin)

Diphyllobothriidea (copepods [→ fishes] → mammals)

Diphyllidea (elasmobranchs inc. rays, sharks)

Trypanorhyncha (fishes/crustaceans/molluscs → bony fishes/selachians)

Bothriocephalidea (crustaceans [→ teleost] → teleost fishes/amphibians)

Litobothriidea (lamniform sharks)

Lecanicephalidea (molluscs → selachians)

Rhinebothriidea (stingrays)

"Tetraphyllidea" (copepods → fishes/decapods/cephalopods → selachians)

"Tetraphyllidea"

Proteocephalidea (crustaceans → inverts/verts → fishes/amphibians/reptiles)

Nippotaeniidea (crustaceans → fishes)

Mesocestoididae (mammals/birds)

Tetrabothriidea (crustaceans?/cephalopods?/teleosts? → seabirds/cetaceans/pinnipeds)

Cyclophyllidea (mammals → mammals, or insects → birds)

tapeworms

The Taeniidae, including species such as the pork tapeworm and the beef tapeworm that often infect humans, may be the most basal of the 12 orders of the Cyclophyllidea. [33]

Interactions with humans

Advertisement offering "sanitized tape worms jar packed" under the heading "Fat! the enemy that is shortening your life - banished!", c. 1900. It promises "no ill effects", but side effects include diarrhoea and abdominal pain. Weight-Loss Ad (FDA 154) (8212182572).jpg
Advertisement offering "sanitized tape worms jar packed" under the heading "Fat! the enemy that is shortening your life - banished!", c. 1900. It promises "no ill effects", but side effects include diarrhoea and abdominal pain.

In culture

In ancient Greece, the comic playwright Aristophanes and philosopher Aristotle described the lumps that form during cysticercosis as "hailstones". [36] In Medieval times, in The Canon of Medicine , completed in 1025, the Persian physician Avicenna recorded parasites including tapeworms. [36] In the Early Modern period, Francesco Redi described and illustrated many parasites, and was the first to identify the cysts of Echinococcus granulosus seen in dogs and sheep as parasitic in origin; a century later, in 1760, Peter Simon Pallas correctly suggested that these were the larvae of tapeworms. [36]

Tapeworms have occasionally appeared in fiction. Peter Marren and Richard Mabey in Bugs Britannica write that Irvine Welsh's sociopathic policeman in his 1998 novel Filth owns a talking tapeworm, which they call "the most attractive character in the novel"; it becomes the policeman's alter ego and better self. [34] Mira Grant's 2013 novel Parasite envisages a world where people's immune systems are maintained by genetically engineered tapeworms. [37]

There are unproven claims that, around 1900, tapeworm eggs were marketed to the public as slimming tablets. [38] A full-page coloured advertisement, purportedly from a women's magazine of that period, reads "Fat: the enemy .. that is banished! How? With sanitized tape worms. Jar packed. No ill effects!" [34] When television presenter Michael Mosley deliberately infected himself with tapeworms he gained weight due to increased appetite. [39] Dieters still sometimes risk intentional infection to become slim, evidenced by a 2013 warning on American television. [40]

Infection and treatment

Like other species of mammal, humans can become infected with tapeworms. There may be few or no symptoms, and the first indication of the infection may be the presence of one or more proglottids in the stools. The proglottids appear as flat, rectangular, whitish objects about the size of a grain of rice, which may change size or move about. Bodily symptoms which are sometimes present include abdominal pain, nausea, diarrhoea, increased appetite and weight loss. [35]

There are several classes of anthelminthic drugs, some effective against many kinds of parasite, others more specific; these can be used both preventatively [41] and to treat infections. [42] For example, Praziquantel is an effective treatment for tapeworm infection, and is preferred over the older niclosamide. Cestodes can also be treated with certain kinds of antibiotics. [43] While accidental tapeworm infections in developed countries are quite rare, such infections are more likely to occur in countries with poor sanitation facilities or where food hygiene standards are low. [35]

Notes

  1. Tapeworms are not formed of fixed body segments as are the annelids, arthropods or chordates.[ citation needed ]

Related Research Articles

Trematoda class of worms

Trematoda is a clade within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes.

<i>Diphyllobothrium</i> genus of worms

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 Diphyllobothrium 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. Other members of the genus Diphyllobothrium include Diphyllobothrium dendriticum, which has a much larger range, D. pacificum, D. cordatum, D. ursi, D. lanceolatum, D. dalliae, and D. yonagoensis, all of which infect humans only infrequently. In Japan, the most common species in human infection is D. nihonkaiense, which was only identified as a separate species from D. latum in 1986. More recently, a molecular study found D. nihonkaiense and D. klebanovskii to be a single species.

Hymenolepiasis is infestation by one of two species of tapeworm: Hymenolepis nana or H. diminuta. Alternative names are dwarf tapeworm infection and rat tapeworm infection. The disease is a type of helminthiasis which is classified as a neglected tropical disease.

<i>Taenia</i> (cestode) genus of tapeworm

Taenia is a genus of tapeworms that includes some important parasites of livestock. Members of the genus are responsible for taeniasis and cysticercosis in humans, which are a type of helminthiasis belonging to the group of neglected tropical diseases. More than 100 species are recorded. They are morphologically characterized by a ribbon-like body composed of a series of segments called proglottids; hence the name Taenia. The anterior end of the body is the scolex. Not all members of the genus Taenia have an armed scolex, for example, Taenia saginata has an unarmed scolex, while Taenia solium has an armed scolex.

<i>Dipylidium caninum</i> species of worm

Dipylidium caninum, also called the flea tapeworm, double-pored tapeworm, or cucumber tapeworm, is a cyclophyllid cestode that infects organisms afflicted with fleas and canine chewing lice, including dogs, cats, and sometimes human pet-owners, especially children.

Hymenolepididae family of worms

The Hymenolepididae are family of cyclophyllid tapeworms. Their characteristic feature is the small number of testes. The unilateral genital pores and large external seminal vesicle allow for easy recognition. Most species are small, transparent, and easy to study. The family contains over 90 genera with over 900 species, having as their definitive host birds or mammals. Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have arthropods as intermediate hosts.

Eucestoda is the larger of the two subclasses of flatworms in the class Cestoda. The Eucestoda are commonly referred to as tapeworms. Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cestodaria. All tapeworms are endoparasites of vertebrates, living in the digestive tract or related ducts. Examples are the pork tapeworm with a human definitive host, and pigs as the secondary host, and Moniezia expansa, the definitive hosts of which are ruminants.

Spirometra erinaceieuropaei is a tapeworm that infects domestic animals and humans. In humans, infection is called sparganosis. S. erinaceieuropaei’s distribution is cosmopolitan, meaning that it can be found nearly anywhere the parasite can complete its lifecycle. This species is closely related to Spirometra mansonoides, and few morphological differences exist between the two. One difference is that the uterus of S. mansonoides is a “U” shape, but in S. erinaceieuropaei the uterus consists of two sections that resemble horns. The life cycle of both species is very similar.

Diphyllobothrium mansonoides is a species of tapeworm (cestodes) that is endemic to North America. Infection with D. mansonoides in humans can result in sparganosis. Justus F. Mueller first reported this organism in 1935. D. mansonoides is similar to D. latum and Spirometra erinacei. When the organism was discovered, scientist did not know if D. mansonoides and S. erinacei were separate species. PCR analysis of the two worms has shown the two to be separate but closely related organisms.

Bertielliasis is the infection of Bertiella - a cestode tapeworm parasite that primarily infects nonhuman primates, rodents and Australian marsupials. Occasionally, human infections have been documented by one of two species: Bertiella studeri, or Bertiella mucronata. These infections present with symptoms similar to most tapeworm cases, and are frequently misdiagnosed. Bertiella transmission is through oribatid mites that are present in the soil of problem areas, and can be easily prevented by avoiding contact with nonhuman primates, rodents and soil in these areas.

<i>Raillietina</i> genus of worms

Raillietina is a genus of tapeworms that includes helminth parasites of vertebrates, mostly of birds. The genus was named in 1920 in honour of a French veterinarian and helminthologist, Louis-Joseph Alcide Railliet. Of the 37 species recorded under the genus, Raillietina demerariensis, R. asiatica, and R. formsana are the only species reported from humans, while the rest are found in birds. R. echinobothrida, R. tetragona, and R. cesticillus are the most important species in terms of prevalence and pathogenicity among wild and domestic birds.

<i>Raillietina echinobothrida</i> parasitic tapeworm belonging to the class Cestoda

Raillietina echinobothrida is a parasitic tapeworm belonging to the class Cestoda. It is the most prevalent and pathogenic helminth parasite in birds, particularly in domestic fowl, Gallus domesticus Linnaeus, 1758. It requires two hosts, birds and ants, for completion of its life cycle. It is a hermaphrodite worm having both the male and female reproductive organs in its body. The parasite is responsible for 'nodular tapeworm disease' in poultry.

Moniezia expansa is commonly known as sheep tapeworm or double-pored ruminant tapeworm. It is a large tapeworm inhabiting the small intestines of ruminants such as sheep, goats and cattle. It has been reported from Peru that pigs are also infected. There is an unusual report of human infection in an Egyptian. It is characterized by unarmed scolex, presence of two sets of reproductive systems in each proglottid, and each proglottid being very short but very broad.

<i>Hymenolepis microstoma</i> species of worm

Hymenolepis microstoma, also known as the rodent tapeworm, is an intestinal dwelling parasite. Adult worms live in the bile duct and small intestines of mice and rats, and larvae metamorphose in the haemocoel of beetles. It belongs to the genus Hymenolepis; tapeworms that cause hymenolepiasis. H. microstoma is prevalent in rodents worldwide, but rarely infects humans.

<i>Raillietina tetragona</i> species of worm

Raillietina tetragona is a parasitic tapeworm belonging to the class Cestoda. It is a cosmopolitan helminth of the small intestine of pigeon, chicken and guinea fowl, and is found throughout the world.

Raillietina cesticillus is a parasitic tapeworm of the family Davaineidae. Sometimes called 'broad-headed tapeworm', it infects the small intestine of chicken and occasionally other birds, such as guinea fowl and turkey, which are generally in close proximity to backyard poultry. It is a relatively harmless species among intestinal cestodes in spite of a high prevalence. In fact it probably is the most common parasitic platyhelminth in modern poultry facilities throughout the world.

Anoplocephala manubriata is a host-specific tapeworm, or cestode, that parasitizes African and Asian elephants. These parasites require intermediate and definitive hosts to complete its life cycle. A. manubriata causes gastrointestinal inflammation in elephants. When ingested in the elephant, the cestode is attached to the intestinal mucosae. The life cycle of A. manubriata have not been completely elucidated, however studies have shown through examining oribatid mites from a dung pile near an elephant site that an immature stage exists. The study concluded at least five species were contained at least one immature life stage of the cestode.

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Further reading