54-471: Echinococcus is a genus within Cestoda , a parasitic class of the platyhelminthes phylum (colloquially known as flatworms). Human echinococcosis is an infectious disease caused by the following species: E. granulosus , E. multilocularis , E. vogeli or E. oligarthrus . Echinococcus is triploblastic – it has three layers – outermost ectoderm , middle mesoderm , and inner endoderm . An anus
108-768: A slimming aid has been touted since around 1900. All 6,000 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. 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). 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). Cestodes have no gut or mouth and absorb nutrients from
162-563: A definitive host for the adult tapeworm. Definitive hosts are where parasites reach maturity and reproduce. Wild or domesticated ungulates , such as sheep, serve as an intermediate host. Transitions between life stages occur in intermediate hosts. The larval stage results in the formation of echinococcal cysts in intermediate hosts. Echinococcal cysts are slow growing, but can cause clinical symptoms in humans and be life-threatening. Cysts may not initially cause symptoms, in some cases for many years. Symptoms developed depend on location of
216-520: A definitive host before larvae infect sheep in the mainland of Australia. Sled dogs may expose moose or reindeer to E. granulosus in parts of North America and Eurasia. E. granulosus requires two host types, a definitive host and an intermediate host. The definitive host of this parasite are dogs and the intermediate host are most commonly sheep, however, cattle, horses, pigs, goats, and camels are also potential intermediate hosts. Humans can also be an intermediate host for E. granulosus , however this
270-403: A gravid proglottid. The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans. The lifecycle of E. granulosus involves dogs and wild carnivores as
324-472: A human becomes infected there are a variety of methods for treatment. The most common treatment in the past years has been surgical removal of the hydatid cysts. The fluid in the cysts contain antigens that can immunologically sensitize the host, so cyst manipulation should be performed with caution, as spilling of cyst contents can cause anaphylactic shock. However, in recent years, less invasive treatments have been developed such as cyst puncture, aspiration of
378-409: 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. Schistocephalus solidus is another three-phase example. The intermediate hosts are copepods and small fish, and
432-442: A scolex (head), a short neck, and a strobila (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
486-401: 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. Though they are sexually hermaphroditic and cross-fertilization is the norm, self-fertilization sometimes occurs and makes possible
540-582: A strobila, or segmented 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. The Cestodaria have 10 larval hooks while Eucestoda have 6 larval hooks. The scolex, which attaches to
594-403: A two-phase life cycle 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
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#1732801759977648-535: Is a sister to the genus Taenia from which it diverged more than 10 million years ago. The genus Echinococcus evolved in North America in canids and began to diversify 5.8 million years ago . In 2020, an international effort of scientists from 16 countries lead to a detailed consensus on terminology, i.e. the terms to be used or rejected for the genetics, epidemiology, biology, immunology and clinical aspects linked with Echinococcus species. There
702-515: Is absent, and it has no digestive system. Its body is covered by tegument and the worm is divided into a scolex, a short neck, and three to six proglottids . Its body shape is ribbon-like. In humans, Echinococcus spp. cause a disease called echinococcosis . The three types of echinococcosis are cystic echinococcosis caused by E. granulosus , alveolar echinococcosis caused by E. multilocularis , and polycystic echinococcosis caused by E. vogeli or E. oligarthrus . A worm's incubation period
756-416: 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. Each proglottid contains an independent reproductive tract, and like some other flatworms, cestodes excrete waste through flame cells ( protonephridia ) located in
810-406: Is harmless in dogs, the larval form can be a huge problem in humans. Although rare, the parasite can form a cyst causing cystic echinococcus also known as hydatid disease. The cyst can cause pressure on surrounding tissue which may lead to abnormal organ function, spontaneous fracture of bones, and other neurological effects. The frequency of offal feedings, the prevalence of the parasites within
864-518: Is no vaccine against Echinococcus multilocularis . However, it is possible to protect humans from the fox tapeworm by deworming the main hosts. Cestoda 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 ribbon-like worms as adults, known as tapeworms . Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into
918-574: 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. Gastrotricha [REDACTED] " Turbellaria " [REDACTED] [REDACTED] [REDACTED] [REDACTED] Mollusca [REDACTED] Annelida [REDACTED] The evolutionary history of
972-447: Is the most effect method for intervening with infection rates. Proper disposal of carcasses and offal after home slaughter is difficult in poor and remote communities and therefore dogs readily have access to offal from livestock, thus completing the parasite cycle of Echinococcus granulosus and putting communities at risk of cystic echinococcosis . Boiling livers and lungs which contain hydatid cysts for 30 minutes has been proposed as
1026-434: Is uncommon and therefore humans are considered an aberrant intermediate host. Echinococcus granulosus is ingested and attaches to the mucosa of the intestines in the definitive host and there the parasite will grow into the adult stages. Adult E. granulosus release eggs within the intestine which will be transported out of the body via feces. When contaminated waste is excreted into the environment, intermediate host has
1080-582: Is usually long and can be up to 50 years. Cystic echinococcosis is mostly found in South and Central America, Africa , the Middle East , China , Italy , Spain , Greece , Russia , and the western United States ( Arizona , New Mexico , and California ). Echinococcosis is a zoonosis . The definitive hosts are carnivorous predators – dogs, wolves, foxes, and lions. The adult tapeworm lives in their small intestines and delivers eggs to be excreted with
1134-513: 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. The adult tapeworm has
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#17328017599771188-444: The hydatid worm or dog tapeworm , is a cyclophyllid cestode that dwells in the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis , also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and
1242-416: 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 . Hosts, whose phylogeny often mirrors that of the parasites ( Fahrenholz's rule ), are indicated in italics and parentheses,
1296-549: The Ediacaran-Cambrian border, has great similarities to present day Cestodians. If correct, this would be the earliest example of a Platyzoan and also one of the earliest bilaterian body-fossils and might thus provide an insight to the living mode of Cestodians before they became specialized parasites. The position of the Cestoda within the Platyhelminthes and other Spiralian phyla based on genomic analysis
1350-434: The body such as the muscle. Here it encysts, forming a cysticercus . The parasite completes its life cycle 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. Another two-phase life cycle is exhibited by Anoplocephala perfoliata , the definitive host being an equine and
1404-474: The cyst, but most occur in the liver, lungs, or both. Echinococcus granulosus was first documented in Alaska but is distributed worldwide. It is especially prevalent in parts of Eurasia, north and east Africa, Australia, and South America. Communities that practice sheep farming experience the highest risk to humans, but wild animals can also serve as an avenue for transmission . For example, dingoes serve as
1458-656: The definitive hosts are waterbirds. This species has been used to demonstrate that cross-fertilisation produces a higher infective success rate than self-fertilisation. 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
1512-409: The environment to infect other organisms. Species of the other subclass, Cestodaria , are mainly fish infecting parasites. 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
1566-420: The gut or body wall to reach the coelom ) 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 life cycle, typically arthropods or other vertebrates. Infections can be long-lasting; in humans, tapeworm infection may last as much as 30 years. No asexual phases occur in
1620-651: The gut, they do not provoke an antibody reaction. 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. The fossil Rugosusivitta , which was found in China at base of the Cambrian deposits in Yunnan just above
1674-558: The host in feces, or migrate outwards as independent motile proglottids. 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. 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
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1728-411: The host's alimentary tract through their specialised neodermal cuticle, or tegument , through which gas exchange also takes place. The tegument also protects the parasite from the host's digestive enzymes and allows it to transfer molecules back to the host. 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
1782-513: 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
1836-409: The host. Clean slaughter and high surveillance of potential intermediate host during slaughter is key in preventing the spread this cestode to its definitive host. It is vital to keep dogs and potential intermediate host as separated as possible to avoid perpetuating infection. According to mathematical modeling, vaccination of intermediate hosts, coupled with dosing definitive hosts with anthelminths
1890-413: The intermediate host an oribatid mite . Diphyllobothrium exhibits a more complex, three-phase life cycle. 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
1944-415: The intermediate host is assumed to retain a greater life expectancy than the definitive host. Diagnosis in the definitive host, the dog, may be done by post mortem examination of the small intestine, or with some difficulty ante mortem by purging with arecoline hydrobromate. Detection of antigens in feces by ELISA is currently the best available technique. The prevalence of Echinococcus granulosus
1998-544: The intestinal wall and is carried by bloodstream to liver, lung, brain, or another organ. It settles there and turns into a bladder-like structure called hydatid cyst . From the inner lining of its wall, protoscoleces (i.e. scoleces with invaginated tissue layers) bud and protrude into the fluid filling the cyst. After the death of the normal intermediate host, its body can be eaten by carnivores suitable as definitive hosts. In their small intestines, protoscoleces turn inside out, attach, and give rise to adult tapeworms, completing
2052-477: 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. 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. Other species have ruffled or leaflike scolices, and there may be other structures to aid attachment. In
2106-404: The larval stage the scolex is similarly shaped and is known as the protoscoleces. 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
2160-521: The length of the strobila. 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). Once anchored to the host's intestinal wall, tapeworms absorb nutrients through their surface as their food flows past them. Cestodes are unable to synthesise lipids, which they use for reproduction, and are therefore entirely dependent on their hosts. The tapeworm body
2214-413: 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. 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
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2268-555: The life cycle, as they do in other flatworms , but the life cycle pattern has been a crucial criterion for assessing evolution among Platyhelminthes. 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
2322-1135: The life-cycle sequence (where known) shown by arrows as (intermediate host 1 [→ intermediate host 2 ] → definitive host) . Alternatives, generally for different species within an order, are shown in square brackets. Gyrocotylidea (fishes) Amphilinidea (crustaceans → fishes/turtles) 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) Echinococcus granulosus Echinococcus granulosus , also called
2376-971: The lifecycle. In humans, the cysts persist and grow for years. They are regularly found in the liver (and every possible organ: spleen, kidney, bone, brain, tongue and skin) and are asymptomatic until their growing size produces symptoms or are accidentally discovered. Disruption of the cysts (spontaneous or iatrogenic e.g. liver biopsy ) can be life-threatening due to anaphylactic shock. Cysts are detected with ultrasound, X-ray computed tomography , or other imaging techniques. Antiechinococcus antibodies can be detected with serodiagnostic tests – indirect fluorescent antibody , complement fixation, ELISA , Western blot , and other methods. A phylogenetic tree has been created for several species in this genus – Echinococcus oligarthrus , Echinococcus vogeli , Echinococcus multilocularis , Echinococcus shiquicus , Echinococcus equinus , Echinococcus ortleppi , and Echinococcus granulosus . The first diverging species are
2430-460: The liquids, the injection of chemicals, and then re-aspiration. Benzimidazole-based chemotherapy is also a new treatment option for humans. In order to prevent transmission to dogs from intermediate hosts, dogs can be given anthelminthic vaccinations. In the case of intermediate hosts, especially sheep, these anthelminthic vaccinations do cause an antigenic response—meaning the body produces specific antibody—however it does not prevent infection in
2484-490: The neotropical endemic species E. oligarthrus and E. vogeli . E. ortleppi and E. canadensis are sister species, as are E. multilocularis and E. shiquicus . E. canadensis is related to E. granulosus . The origin of these parasites based on host-parasite co-evolution comparisons was North America or Asia, depending on whether the ancestral definitive hosts were canids or felids . Echinococcus oligarthrus and Echinococcus vogeli are basal in this genus. The genus
2538-469: The offal, and the age of the intermediate host are factors that affect infection pressure within the definitive host. The immunity of both the definitive and intermediate host plays a large role in the transmission of the parasite, as well as the contact rate between the intermediate and the definitive host (such as herding dogs and pasture animals being kept in close proximity where dogs can contaminate grazing areas with fecal matter). The life expectancy of
2592-411: The parasite, coupled with the frequency of anthelminthic treatments, will also play a role in the rate of infection within a host. The temperature and humidity of the environment can affect the survival of E. granulosus . Once sheep are infected, the infection typically remains within the sheep for life. However, in other hosts, such as dogs, treatment for annihilating the parasite is possible. However,
2646-437: The potential to contract the parasite by grazing in contaminated pasture, perpetuating the cycle. Echinococcus granulosus is transmitted from the intermediate host (sheep) to the definitive host (dogs) by frequent feeding of offal , also referred to as "variety meat" or "organ meat". Consuming offal containing E. granulosus can lead to infection; however, infection is dependent on many factors. While adult E. granulosus
2700-421: The proglottids. 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. Mature proglottids are essentially bags of eggs, each of which is infective to the proper intermediate host. They are released and leave
2754-420: The reproduction of a worm when it is the only individual in its host's gut. During copulation, the cirri of one individual connect with those of the other through the genital pore, and then spermatozoa are exchanged. 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
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#17328017599772808-407: The stool. The intermediate hosts are infected by ingesting eggs. Sheep, goats, cattle, camels, pigs, wild herbivores, and rodents are the usual intermediate hosts, but humans can also be infected. Humans are dead-end hosts, since their corpses are nowadays seldom eaten by carnivorous predators. The egg hatches in the digestive system of the intermediate host, producing a planula larva. It penetrates
2862-478: The terrestrial Cyclophyllidea, proglottids are released steadily over a period of years, or as long as their host lives (iteroparity). 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. Many tapeworms have
2916-468: Was found to be 4.35% in a 2008 study in Bangalore , India employing this coproantigen detection technique. Polymerase chain reaction (PCR) is also used to identify the parasite from DNA isolated from eggs or feces. However, it is difficult to determine the eggs in feces because it is indistinguishable from other taeniid eggs. Diagnosis in humans can be done by x-rays, CAT scans, and ultrasounds. If
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