Eucestoda
Eucestoda | |
---|---|
Taenia saginata adult | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Platyhelminthes |
Class: | Cestoda |
Subclass: | Eucestoda |
Eucestoda, commonly referred to as tapeworms, is the larger of the two
Body structure
Adult Eucestoda have a white-opaque dorso-ventrally flattened appearance, and are elongated, ranging in length from a few millimeters (about ¼") to 25 meters (80').
The scolex, located at the anterior end, is a small (usually less than 1 mm)
Members of the Eucestoda have no mouth or digestive tract, and instead absorb nutrients through a layer of microtriches over the tegument at the shared body wall surface.[3] In addition to the body wall, several other systems are common to the whole length of the tapeworm, including excretory canals, nerve fibers, and longitudinal muscles.[4] The excretory system is responsible for osmoregulation and consists of blind-ending flame bulbs communicating through a duct system. The nervous system, often referred to as a "ladder system," is a system of longitudinal connectives and transverse ring commissures.[5]
Reproduction
The reproductive systems develop progressively along the differentiated
Proglottids
An atrium on the lateral margin of each proglottid contains the openings to both the male and female genital ducts. Follicular testes produce sperm, which are carried by a system of ducts to the cirrus, an eversible copulatory organ that usually has a hypodermic system of spines and a holdfast system of hooks. The main specialized female reproductive organs are an ovary that produces eggs and a vitellarium that produces yolk cells. Yolk cells travel in a duct system to the oviduct, where, in a modified region, the ovum is enclosed in a shell with yolk cells. After the gonads and their ducts have finished maturing, the female reproductive organs begin to mature. The oviduct develops a vagina and enlarges into the uterus, where fertilization and embryonic development occur.[5]
Some members of the Eucestoda (such as Echinococcus, Sparganum, Taenia multiceps sp., and Mesocestoides sp.) can reproduce asexually through budding,[5] which initiates a metagenesis of alternating sexually and asexually reproducing generations.[4]
Life stages
A tapeworm can live from a few days to over 20 years.[5] Eucestoda ontogenesis continues through metamorphosing in different larval stages inside different hosts. The initial six-hooked embryo, known as an oncosphere or hexacanth, forms through cleavage. In the order Pseudophyllidea, it remains enclosed in a ciliated embryophore. The embryo continues to develop in other host species, with two intermediate hosts generally needed.[5] It gains entry to its first intermediate host by being eaten.
Except for members of the order Taeniidae, the first intermediate host is an arthropod, and except for in the case of Archigetes spp. (which can attain sexual maturity in freshwater oligochaeta), the second host is usually a fish, but can be another invertebrate or vertebrate.[4] After the scolex has differentiated and matured in the larval stage, growth will stop until a vertebrate eats the intermediate host, and then the strobila develops. Adult tapeworms often have a high final host specificity, with some species only found in one host vertebrate.[5]
Common infective species
Final host | Species |
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Humans | Diphyllobothrium latum, Spirometra erinacea euopaei, Taenia solium, T. saginata, T. asiatica, Mesocestoides leptothylacus (rarely), Rodentoleptis (syn. Vampiro-, Hymenoleptis) nana, Hymenoleptis diminuta
|
Cats | Diphyllobothrium latum, Spirometra erinacea euopaei, T. pisiformis, Echinococcus multilocularis, Dipylidium caninum |
Dogs | Diphyllobothrium latum, Spirometra erinacea euopaei, |
Fish | Caryophyllaeus laticeps, Glaridacris catostomi, Archigetes sieboldi, Triaenophorus sp., Eubothrium sp., Rhinobothrium sp., Phyllobothrium sp., Proteocephalus ambloplites |
Fish-Eating Birds | Ligula intestinalis, Schistocephalus solidus |
Rodents | Schistocephalus solidus, Rodentoleptis nana, Hymenolepis diminuta |
Horses | Anoplocephala magna, Anoplocephala perfoliata |
Ruminants | Moniezia expans, Avitellina sp., Thysaniezia sp., Stilesia sp. |
Chickens | Davainea proglottina, Raillietina tetragona, Amoebotaenia sp., Choanataenia sp., Hymenolepis carioca |
Foxes | |
Lagomorphs | Cittotaenia sp.[4] |
Medical importance
Taeniasis
Cysticercosis
Cysticercosis is a tissue infection caused by the young form of the pork tapeworm.[9][10] Infection occurs through swallowing or antiperistaltic contractions during regurgitation carrying eggs or gravid proglottids to the stomach. At this point, larvae hatch when exposed to enzymes and penetrate the intestinal wall, travelling through the body through blood vessels to tissues like the brain, the eye, muscles, and the nervous system (called neurocysticercosis).[5]
At these sites, the parasites lodge and form cysts, a condition called cysticercosis, producing inflammatory reactions and clinical issues when they die, sometimes causing serious or fatal damage. In the eye, the parasites can cause visual loss, and infection of the spine and adjacent leptomeninges can cause paresthesias, pain, or paralysis.[11]
Echinococcosis (hydatid disease)
Humans become accidental hosts to worms of the genus Echinococcus, playing no role in the worm's biological cycle. This can result in echinococcosis, also called hydatid disease. Humans (usually children) become infected by direct contact with dogs and eating food contaminated with dog feces. Common sites of infection are the liver, the lungs, muscles, bones, kidneys, and the spleen.[12]
Eggs hatch in the gastrointestinal tract after the consumption of contaminated food, after which the larvae travel to the liver through portal circulation. Here, the larvae are trapped and usually develop into hydatid cysts. While the liver is the first filter for trapping them, the lungs act as the second filter site, trapping most of the larvae that are not trapped by the liver. Some larvae escape from the lungs to cause cysts in other tissues.[5]
When a larva becomes established in tissue, it develops into a "bladderworm" or "hydatid" and can cause various cancer-like cysts that may rupture and interact with nearby organs. Most cases are asymptomatic, and the mortality rate is low, but various complications from these interactions may lead to debilitating illness.
Hymenolepiasis
While light infections are usually asymptomatic, autoinfection through eating the eggs of worms in the intestines is possible, and it can lead to hyperinfection. Humans can also become hyperinfected through ingesting grain products contaminated by infected insects. Infections involving more than two thousand worms can cause many different gastrointestinal symptoms and allergic responses. Common symptoms include chronic urticaria, skin eruption, and phlyctenular keratoconjunctivitis.[13]
Diphyllobothriasis
Diphyllobothriasis is caused by infection with Diphyllobothrium latum (also known as the "broad tapeworm" or "fish tapeworm") and related species. Humans become infected by eating raw, undercooked, or marinated fish acting as a second intermediate or paratenic host harboring metacestodes or plerocercoid larvae.[14]
Clinical symptoms are due to the large size of the tapeworm, which often reaches a length exceeding 15 m (49 ft). The most common symptom is pernicious anemia, caused by the absorption of vitamin B12 by the worm.[5] Other symptoms include various intestinal issues, slight leukocytosis, and eosinophilia.
Sparganosis
Sparganosis is caused by the plerocercoid larvae of the tapeworm Spirometra. Humans become infected by drinking contaminated water, eating raw or poorly cooked infected flesh, or from using poultices of raw infected flesh (usually raw pork or snake) on skin or mucous membranes.[15]
The most common symptom is a painful, slowly growing nodule in the subcutaneous tissues, which may migrate. Infection in the eye area can cause pain, irritation, edema, and excess watering. When the orbital tissues become infected, the swelling can cause blindness. An infected bowel may become perforated. Brain infection can cause granulomas, hematomas, and abscesses.
Subdivisions
The evolutionary history of the Eucestoda has been studied using
Cestoda |
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References
- ^ "Tapeworm infection - Symptoms, diagnosis and treatment | BMJ Best Practice". bestpractice.bmj.com.
- ^ a b Mehlhorn, Heinz. "Eucestoda Classification." Encyclopedia of Parasitology. 2008. p. 495-497
- ^ Rohde, Klaus. "Eucestoda." AccessScience. McGraw-Hill Ryerson
- ^ a b c d e f "Encyclopedia of Parasitology"
- ^ a b c d e f g h i j k l m n "AccessScience"
- ^ a b c "CDC - Taeniasis". www.cdc.gov. 24 April 2019. Retrieved 16 December 2019.
- ^ "CDC - Taeniasis - Biology". www.cdc.gov. 24 April 2019. Retrieved 16 December 2019.
- ^ a b "CDC - Taeniasis - General Information - Frequently Asked Questions (FAQs)". www.cdc.gov. 24 April 2019. Retrieved 16 December 2019.
- ISBN 978-0-07-302827-9.
- ^ "Taeniasis/Cysticercosis Fact sheet N°376". World Health Organization. February 2013. Archived from the original on 15 March 2014. Retrieved 18 March 2014.
- ^ Bale, James F. "Cysticercosis." Current Treatment Options in Neurology. 2000. p. 355360
- ^ Usharani, A., et al. "Case Reports of Hydatid Disease." Journal of Epidemiology and Global Health. 2013. p. 63–66
- ^ Kim, Bong Jin, et al. "Heavy Hymenoleptis nana Infection Possibly Through Organic Food: Report of a Case." The Korean Journal of Parasitology. 2014. p. 85–87
- ^ Esteban, J. G., Munoz-Antoli, C., and R. Toledo. "Human Infection by a "Fish Tapeworm," Diphyllobothrium latum, in a Non-Endemic Country." Infection. 2014. p. 191–194
- ^ Dunn, J., and Philip E.S. Palmer. "Sparganosis." Seminars in Roentgenology. 1998. p. 86–88
- PMID 17950292.
- S2CID 6288037.
- PMID 22406529.
- Bale, James F. "Cysticercosis." Current Treatment Options in Neurology. 2000. pp. 355–360.
- Dunn, J., and Philip E. S. Palmer. "Sparganosis." Seminars in Roentgenology. 1998. pp. 86–88.
- Esteban, J. G., Munoz-Antoli, C., and R. Toledo. "Human Infection by a "Fish Tapeworm," Diphyllobothrium latum, in a Non-Endemic Country." Infection. 2014. pp. 191–194.
- Kim, Bong Jin, et al. "Heavy Hymenoleptis nana Infection Possibly Through Organic Food: Report of a Case." The Korean Journal of Parasitology. 2014. pp. 85–87.
- Mehlhorn, Heinz. "Eucestoda Classification." Encyclopedia of Parasitology. 2008. pp. 495–497.
- Rohde, Klaus. "Eucestoda." AccessScience. McGraw-Hill Ryerson.
- Usharani, A., et al. "Case Reports of Hydatid Disease." Journal of Epidemiology and Global Health. 2013. p. 63–66.