Echinococcus

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Echinococcus
Cotton rat infected with Echinococcus multilocularis 3MG0020 lores.jpg
Necropsy of a cotton rat infected with Echinococcus multilocularis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Taeniidae
Genus: Echinococcus
Rudolphi, 1801
schematic representation of the life cycle of Echinococcus CDC Echinococcus Life Cycle.svg
schematic representation of the life cycle of Echinococcus
General description of the egg and oncosphere of Echinococcus spp. Vuitton et al - International consensus on terminology - parasite200043-fig2ab.png
General description of the egg and oncosphere of Echinococcus spp.

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 [1] [2] or E. oligarthrus . [2]

Contents

Echinococcus is triploblastic – it has three layers – outermost ectoderm, middle mesoderm, and inner endoderm. An anus 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. [3] A worm's incubation period 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 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 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 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. [4]

Taxonomy

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 . [5] The first diverging species are 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. [6] The genus 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. [7]

Prevention

There is no vaccine against Echinococcus multilocularis . However, it is possible to protect humans from the fox tapeworm by deworming the main hosts. [8] [ self-published source ]

Related Research Articles

<span class="mw-page-title-main">Echinococcosis</span> Parasitic disease of tapeworms of the Echinococcus type

Echinococcosis is a parasitic disease caused by tapeworms of the Echinococcus type. The two main types of the disease are cystic echinococcosis and alveolar echinococcosis. Less common forms include polycystic echinococcosis and unicystic echinococcosis.

<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.

Alveolar hydatid disease (AHD) is a form of echinococcosis, or a disease that originates from a parasitic flatworm. AHD is caused by an infection of the flatworm species Echinococcus multilocularis. Although alveolar echinococcosis is rarely diagnosed in humans and is not as widespread as cystic echinococcosis, it is also still a serious disease that has a significantly high fatality rate. It is considered one of the most life-threatening helminthic infections humans can have.

<i>Taenia</i> (flatworm) 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>Echinococcus granulosus</i> Species of flatworm

Echinococcus granulosus, also called 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 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.

<i>Echinococcus multilocularis</i> Species of flatworm

Echinococcus multilocularis, the fox tapeworm, is a small cyclophyllid tapeworm found extensively in the northern hemisphere. E. multilocularis, along with other members of the Echinococcus genus, produce diseases known as echinococcosis. Unlike E. granulosus,E. multilocularis produces many small cysts that spread throughout the internal organs of the infected animal. The resultant disease is called alveolar echinococcosis, and is caused by ingesting the eggs of E. multilocularis.

<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.

<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.

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.

Hans Vogel was a German scientist known for his work in helminthology. For much of his career he was associated with the Bernhard Nocht Institute for Tropical Medicine in Hamburg.

<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">Coenurosis</span> Parasitic disease

Coenurosis, also known as caenurosis, coenuriasis, gid or sturdy, is a parasitic infection that develops in the intermediate hosts of some tapeworm species. It is caused by the coenurus, the larval stage of these tapeworms. The disease occurs mainly in sheep and other ungulates, but it can also occur in humans by accidental ingestion of tapeworm eggs.

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

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.

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>Echinococcus vogeli</i> Species of flatworm

Echinococcus vogeli is a small cyclophyllid tapeworm found in Central and South America. E. vogeli, as well as other members of the genus Echinococcus, produce a disease called echinococcosis. Echinococcosis, also known has hydatidosis, is a result of ingesting the eggs of the genus Echinococcus. E. vogeli is similar to E. multilocularis in that both species produces many small cysts that spread throughout the internal organs of the infected animal. The ingestion of E. vogeli eggs, and the spreading of the cysts through infected host, will results in Polycystic Echinococcosis.

<span class="mw-page-title-main">Cat worm infections</span> Worm infections in cats

Cat worm infections, the infection of cats (Felidae) with parasitic worms, occur frequently. Most worm species occur worldwide in both domestic and other cats, but there are regional, species and lifestyle differences in the frequency of infestation. According to the classification of the corresponding parasites in the zoological system, infections can be divided into those caused by nematode and flatworms - in the case of the latter, mainly cestoda and trematoda - while other strains are of no veterinary significance. While threadworms usually do not require an intermediate host for their reproduction, the development cycle of flatworms always proceeds via alternate hosts.

References

  1. Dandan, Imad (7 May 2019). "Hydatid Cysts" . Medscape. Retrieved 24 November 2023.
  2. 1 2 "Echinococcosis". DPDx - Laboratory Identification of Parasites of Public Health Concern. Centers for Disease Control and Prevention. 15 July 2019. Retrieved 24 November 2023.
  3. Thompson RC, McManus DP (2001). "Chapter 1: Aetiology: parasites and life cycles". In Eckert J, Gemmell MA, Meslin FX, Pawłowski ZS (eds.). WHO/OIE Manual on Echinococcosis in Humans and Animals: a Public Health Problem of Global Concern. Paris: Office International des Epizooties. pp. 1–19. ISBN   92-9044-522-X . Retrieved 24 November 2023 via World Health Organization.
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