Cysticercus

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Drawing of Cysticerus cellulosae: Left one from the pig showing an invaginated scolex. Right one from human intestine showing the evaginated scolex. Finne bewaffneter Bandwurm-drawing.jpg
Drawing of Cysticerus cellulosae: Left one from the pig showing an invaginated scolex. Right one from human intestine showing the evaginated scolex.

Cysticercus (pl. cysticerci) is a scientific name given to the young tapeworms (larvae) belonging to the genus Taenia . It is a small, sac-like vesicle resembling a bladder; hence, it is also known as bladder worm. It is filled with fluid, in which the main body of the larva, called scolex (which will eventually form the head of the tapeworm), resides. It normally develops from the eggs, which are ingested by the intermediate hosts, such as pigs and cattle. The tissue infection is called cysticercosis. Inside such hosts, they settle in the muscles. When humans eat raw or undercooked pork or beef that is contaminated with cysticerci, the larvae grow into adult worms inside the intestine. Under certain circumstances, specifically for the pork tapeworm, the eggs can be accidentally eaten by humans through contaminated foodstuffs. In such case, the eggs hatch inside the body, generally moving to muscles as well as inside the brain. Such brain infection can lead to a serious medical condition called neurocysticercosis. [1] This disease is the leading cause of acquired epilepsy. [2]

Contents

Discovery and naming system

Cysticercus was discovered in the late 17th century CE as a parasitic bladder. It was believed to be a different organism from the adult tapeworm ( Taenia solium ), but still closely related to tapeworms for their similar-looking scolices. Hence, it was given a proper scientific name Taenia cellulosae in 1800 by German naturalist Johann Friedrich Gmelin. At the same time, another German, Johann Zeder, had created a new genus Cysticercosis for a dog tapeworm. This genus was accepted for all bladder worms of Taenia. [3] It became a tradition to refer to the larva of Taenia solium as Cysticercus cellulosae, that of beef tapeworm ( T. saginata ) as Cysticercus bovis, that of sheep tapeworm (T. ovis) as Cysticercus ovis, that of ruminant tapeworm (T. krabbei) as Cysticercus tarandi, and that of the dog tapeworm (T. crassiceps) as Cysticercus longicollis. [4] [5] Though this system of naming is now scientifically unacceptable, it is still widely used, particularly for description of the infections by the different species. [6]

Structure

Resected gross specimen of cysicercus from the human brain, (a) and photomicrograph of hematoxylin and eosin stained section, (b) cysticercus cellulosae with an undulating bladder wall and scolex. Three suckers along with rows of hooklets (arrow) can be identified on the scolex (x200, original magnification) Cysticercus cellulosae.jpg
Resected gross specimen of cysicercus from the human brain, (a) and photomicrograph of hematoxylin and eosin stained section, (b) cysticercus cellulosae with an undulating bladder wall and scolex. Three suckers along with rows of hooklets (arrow) can be identified on the scolex (×200, original magnification)

A cysticercus is a bladder-like transparent vesicle. It is composed of two main parts: the vesicular wall and a scolex. The vesicular wall is a complex structure made up of three distinct layers. The outermost is a smooth and undifferentiated layer called cuticular mantle. The middle is composed of cells that resemble epithelial cells. The innermost is made up of muscle and other fibres. Inside the vesicular wall is an invaginated (facing inward) scolex. The scolex contains suckers and hooks, and a neck attached to a rudimentary body segment. [1] [7]

Pathogenicity

In the normal life cycle of Taenia, cysticerci develop in the muscles of the intermediate hosts such as pigs, cattle, and sheep. In these animals, they do not cause severe symptoms. They are transmitted to humans when their infected meats are eaten. [8] [9] However, T. solium is unusual because its cysticerci can develop in humans. Due to accidental consumption of the eggs from contaminated foodstuffs, cysticerci in humans produce clinical symptoms, cysticercosis. Thus, humans are accidental intermediate hosts. [10]

Related Research Articles

<span class="mw-page-title-main">Cysticercosis</span> Tissue infection caused by the young form of the pork tapeworm

Cysticercosis is a tissue infection caused by the young form of the pork tapeworm. People may have few or no symptoms for years. In some cases, particularly in Asia, solid lumps of between one and two centimetres may develop under the skin. After months or years these lumps can become painful and swollen and then resolve. A specific form called neurocysticercosis, which affects the brain, can cause neurological symptoms. In developing countries this is one of the most common causes of seizures.

<span class="mw-page-title-main">Praziquantel</span> Medication

Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat schistosomiasis, clonorchiasis, opisthorchiasis, tapeworm infections, cysticercosis, echinococcosis, paragonimiasis, fasciolopsiasis, and fasciolosis. It should not be used for worm infections of the eye. It is taken by mouth.

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

Taenia solium, the pork tapeworm, belongs to the cyclophyllid cestode family Taeniidae. It is found throughout the world and is most common in countries where pork is eaten. It is a tapeworm that uses humans as its definitive host and pigs as the intermediate or secondary hosts. It is transmitted to pigs through human feces that contain the parasite eggs and contaminate their fodder. Pigs ingest the eggs, which develop into larvae, then into oncospheres, and ultimately into infective tapeworm cysts, called cysticercus. Humans acquire the cysts through consumption of uncooked or under-cooked pork and the cysts grow into an adult worms in the small intestine.

<i>Taenia</i> (tapeworm) Genus of flatworms

Taenia is the type genus of the Taeniidae family of tapeworms. It includes some important parasites of livestock. Members of the genus are responsible for taeniasis and cysticercosis in humans, which are types 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. Some members of the genus Taenia have an armed scolex ; of the two major human parasites, Taenia saginata has an unarmed scolex, while Taenia solium has an armed scolex.

<i>Taenia saginata</i> Species of flatworm

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.

<i>Taenia crassiceps</i> Species of Cestoda

Taenia crassiceps is a tapeworm in the family Taeniidae. It is a parasitic organism whose adult form infects the intestine of carnivores, like canids. It is related to Taenia solium, the pork tapeworm, and to Taenia saginata, the beef tapeworm. It is commonly found in the Northern Hemisphere, especially throughout Canada and the northern United States.

<span class="mw-page-title-main">Taeniidae</span> Family of flatworms

The Taeniidae are a family of tapeworms. It is the largest family representing the order Cyclophyllidea. It includes many species of medical and veterinary importance, as Taenia solium, Taenia saginata, and Echinococcus granulosus. The Taeniidae are parasites of mammals and many are infectious to humans.

<i>Taenia pisiformis</i> Species of flatworm

Taenia pisiformis, commonly called the rabbit tapeworm, is an endoparasitic tapeworm which causes infection in lagomorphs, rodents, and carnivores. Adult T. pisiformis typically occur within the small intestines of the definitive hosts, the carnivores. Lagomorphs, the intermediate hosts, are infected by fecal contamination of grasses and other food sources by the definitive hosts. The larval stage is often referred to as Cysticercus pisiformis and is found on the livers and peritoneal cavities of the intermediate hosts. T. pisiformis can be found worldwide.

<span class="mw-page-title-main">Taeniasis</span> Parasitic disease due to infection with tapeworms belonging to the genus Taenia

Taeniasis is an infection within the intestines by adult tapeworms belonging to the genus Taenia. There are generally no or only mild symptoms. Symptoms may occasionally include weight loss or abdominal pain. Segments of tapeworm may be seen in the stool. Complications of pork tapeworm may include cysticercosis.

<span class="mw-page-title-main">Eucestoda</span> Subclass of flatworms

Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda. 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.

Sparganosis is a parasitic infection caused by the plerocercoid larvae of the genus Spirometra including S. mansoni, S. ranarum, S. mansonoides and S. erinacei. It was first described by Patrick Manson from China in 1882, and the first human case was reported by Charles Wardell Stiles from Florida in 1908. The infection is transmitted by ingestion of contaminated water, ingestion of a second intermediate host such as a frog or snake, or contact between a second intermediate host and an open wound or mucous membrane. Humans are the accidental hosts in the life cycle, while dogs, cats, and other mammals are definitive hosts. Copepods are the first intermediate hosts, and various amphibians and reptiles are second intermediate hosts.

<span class="mw-page-title-main">Neurocysticercosis</span> Cysticercosis of the brain

Neurocysticercosis is a specific form of the infectious parasitic disease cysticercosis that is caused by the infection with Taenia solium, a tapeworm found in pigs. Neurocysticercosis occurs when cysts formed by the infection take hold within the brain, causing neurologic syndromes such as epileptic seizures. It is a common cause of seizures worldwide. It has been called a "hidden epidemic" and "arguably the most common parasitic disease of the human nervous system". Common symptoms of neurocysticercosis include seizures, headaches, blindness, meningitis and dementia.

Professor Marshall Lightowlers began his career in the field of parasitology during a post-doctoral appointment at the Institute of Medical and Veterinary Science in Adelaide where he undertook research on ovine sarcocystosis. In 1981 he began a post-doctoral position at The University of Melbourne, Veterinary Clinical Centre and commenced a research career focusing on the immunology and molecular biology of taeniid cestode parasites. His initial research at the University of Melbourne investigated the immunochemistry of antigens of Taenia taeniaeformis and Echinococcus granulosus. Subsequently he was a member of a team of scientists that developed a vaccine against Taenia ovis infection in sheep, the first recombinant vaccine against a parasitic disease. In 1989 Lightowlers took over leadership of the molecular parasitology research laboratories at the University of Melbourne and began applying the lessons learnt with T. ovis to the development of similar vaccines against infection with the larval stages of other cestode parasites. This led to the development of highly effective, recombinant vaccines against cysticercosis in cattle due to Taenia saginata (TSA9/TSA18) and in pigs due to Taenia solium. In collaboration with Dr David Heath at the Wallaceville Animal Research Centre in New Zealand, he and his colleagues also developed the EG95 recombinant vaccine against cystic echinococcosis.

<span class="mw-page-title-main">Cestoda</span> Class of flatworms

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 the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish infecting parasites.

Human parasites include various protozoa and worms.

<span class="mw-page-title-main">Coenurosis in humans</span> Medical condition

Coenurosis is a parasitic infection that results when humans ingest the eggs of dog tapeworm species Taenia multiceps, T. serialis, T. brauni, or T. glomerata.

Taenia asiatica, commonly known as Asian taenia or Asian tapeworm, is a parasitic tapeworm of humans and pigs. It is one of the three species of Taenia infecting humans and causes taeniasis. Discovered only in 1980s from Taiwan and other East Asian countries as an unusual species, it is so notoriously similar to Taenia saginata, the beef tapeworm, that it was for a time regarded as a slightly different strain. But anomaly arose as the tapeworm is not of cattle origin, but of pigs. Morphological details also showed significant variations, such as presence of rostellar hooks, shorter body, and fewer body segments. The scientific name designated was then Asian T. saginata. But the taxonomic consensus turns out to be that it is a unique species. It was in 1993 that two Korean parasitologists, Keeseon S. Eom and Han Jong Rim, provided the biological bases for classifying it into a separate species. The use of mitochondrial genome sequence and molecular phylogeny in the late 2000s established the taxonomic status.

<span class="mw-page-title-main">Friedrich Küchenmeister</span>

Gottlieb Heinrich Friedrich Küchenmeister was a German physician.

Taenia serialis, also known as a canid tapeworm, is found within canines such as foxes and dogs. Adult T. serialis are parasites of carnivores, particularly dogs, with herbivorous lagomorph mammals such as rabbits and hares, serving as intermediate hosts. In definitive hosts, T. serialis is acquired by eating tissues from a variety of intermediate hosts. Accidental infection of humans though, can occur when eggs are ingested from food or water contaminated with dog feces and the human then becomes the T. serialis intermediate host.

<i>Taenia hydatigena</i> Species of flatworm

Taenia hydatigena is one of the adult forms of the canine and feline tapeworm. This infection has a worldwide geographic distribution. Humans with taeniasis can infect other humans or animal intermediate hosts by eggs and gravid proglottids passed in the feces.

References

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