Echinococcus multilocularis

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Echinococcus multilocularis
Echinococcus multilocularis.jpg
Echinococcus multilocularis isolated from a fox
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Taeniidae
Genus: Echinococcus
Species:
E. multilocularis
Binomial name
Echinococcus multilocularis
Leuckart, 1863
Synonyms
  • Echinococcus sibiricensisRausch & Schiller 1954 (Vogel 1957) [1]
  • Alveococcus multilocularisLukashenko 1968 [1]
  • Echinococcus russicensisTang et al 2007 (Nakao et al 2009, Ito et al 2010) [1]

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 (especially E. granulosus ), produce diseases known as echinococcosis. Unlike E. granulosus,E. multilocularis produces many small cysts (also referred to as locules) 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.

Contents

The parasite is commonly maintained in a wildlife life cycle involving two mammalian hosts. Wild canids, dogs, and less commonly cats act as definitive hosts, harbouring the adult stage of the tape worm. Voles are the intermediate hosts. [1] Ingestion of a rodent containing alveolar hydatid cysts by a wild canid can result in a heavy infestation of tapeworms.

Signs and symptoms

Human alveolar echinococcosis is characterized by a lengthy incubation period of 5 to 15 years in immunocompetent individuals. The progression of disease is potentiated in immunocompromised patients. Following the ingestion of the eggs of E. multilocularis, the metacestode (larval) stage of the parasite typically embeds in the liver. As the disease progresses, the larval stage proliferates exogenously within the tissue, behaving similar to hepatic neoplasia. Patients with human alveolar echinococcosis typically present with headache, nausea, vomiting, abdominal pain. Jaundice is rare, [2] but hepatomegaly is a common physical finding.

Life cycle

The life cycle of E. multilocularis involves a primary or definitive host and a secondary or intermediate host, each harboring different life stages of the parasite.

Foxes, coyotes, domestic dogs, and other canids are the definitive hosts for the adult stage of the parasite. Cats may also be involved. [3] The head of the tapeworm attaches to the intestinal mucosa by hooks and suckers. It then produces hundreds of microscopic eggs, which are dispersed through the feces. [4]

Voles are the intermediate host. [1] Beavers may also be affected; and reintroduction of beavers from affected areas is a cause for concern. [5] Eggs ingested by rodents develop in the liver, lungs and other organs to form multilocular cysts. The life cycle is completed after a fox or canine consumes a rodent infected with cysts. Larvae within the cyst develop into adult tapeworms in the intestinal tract of the definitive host. [4]

Humans can become an aberrant intermediate host by accidentally ingesting eggs of E. multilocularis when handling infected animals or consuming contaminated food, vegetable, and water. Except in rare cases where infected humans are eaten by canines, humans are a dead-end or incidental host (an aberrant intermediate host that does not allow transmission to the definitive host) for E. multilocularis.[ citation needed ]

Summary of the life cycle
  1. adult worm present in intestine of definitive host
  2. eggs passed in feces, ingested by humans or intermediate host
  3. onchosphere penetrates intestinal wall, carried via blood vessels to lodge in organs
  4. hydatid cysts develop in liver, lungs, brain, heart
  5. protoscolices (hydatid sand) ingested by definitive host
  6. ingested protoscolices attach to small intestine and develops into adult worm

Morphology

Cotton rat infected with Echinococcus multilocularis Cotton rat infected with Echinococcus multilocularis 3MG0020 lores.jpg
Cotton rat infected with Echinococcus multilocularis

The adult parasite is a small tapeworm that is 3-6 mm long, and lives in the small intestine of canines. The segmented worm contains a scolex with suckers and hooks that enable attachment to the mucosal wall, since tapeworms do not have a digestive tract. A short neck connects the head to three proglottids, the body segment of the worm which contains the eggs to be excreted in the feces. [6]

Diagnosis

Serological and imaging tests are commonly used to diagnose this disease. Since the serological tests for alveolar echinococcosis only indicate exposure to the parasite and not ongoing infection, visualization of the parasitic mass is required to confirm the diagnosis. Frequently used serological tests include antibody tests, ELISA and indirect hemaglutination (IHA). An intradermal allergic reaction test (Casoni test) has also been used to diagnose patients. Imaging tests include: X-rays, CT scans, MRI, and ultrasound. [2] Histology is another important diagnostic tool to use. In the past, the PAS staining technique has proven beneficial in helping determine if infections are caused by Echinococcus multiocularis. More recently, a new immunohistochemistry technique that uses a monoclonal antibody (Em2G11) has provided professionals with more accuracy and precision in diagnosing Echinococcus multiocularis and distinguishing it from other species like Echinococcus granulosus. [7]

Disease staging

Alveolar echinococcosis (AE) is a highly lethal helminthic disease in humans, caused by the larval form of the parasitic tapeworm E. multilocularis. The disease represents a serious public threat in China, Siberia, and central Europe. However, since the 1990s, the prevalence of the disease seems to be increasing in Europe, not only in the historically endemic areas but its neighboring regions. [8] AE primarily affects the liver by inducing a hepatic disorder similar to liver cancer, therefore becoming extremely dangerous and difficult to diagnose. If the infection metastasizes, it may spread to any other organ and could be lethal if not treated. The most common treatment for AE is to surgically remove the parasite. Since it is difficult and not always possible to remove the entire parasite, medicine such as Albendazole is utilized to keep the cyst from growing back. [4]

Guided by the Tumor-Node-Metastasis (TNM) system of liver cancer, the European Network for Concerted Surveillance of Alveolar Echinococcosis and the World Health Organization Informal Working Group on Echinococcosis, a clinical classification system has been proposed. This classification system has been designated as the "PNM" system (P = parasitic mass, N = involvement of neighboring organs, M = metastasis). The system was developed by a retrospective analysis of records from 97 patients treated in France and Germany (2 treatment centers). Amongst other characteristics, the system takes into consideration the localization of the parasite in the liver, the extent of lesion involvement, regional involvement, and metastasis. [9]

Treatment

If no specific therapy is initiated, in 94% of patients the disease is fatal within 10–20 years following diagnosis. [10]

Epidemiology

Epidemiology of Echinococcus multilocularis in Canada Parasite140082-fig1 Echinococcus multilocularis in Canada.png
Epidemiology of Echinococcus multilocularis in Canada

The incidence of human infestation with E. multilocularis and disease is increasing in urban areas, as wild foxes (an important reservoir species of the sylvatic cycle) are migrating to urban and suburban areas and gaining closer contact with human populations. [4] Also, restocking fox enclosures for fox hunting with infected animals spreads the disease. [14] Children, health care workers and domestic animals are at risk of ingesting the eggs after coming into contact with the feces of infected wild foxes. Even with the improvement of health in developed/industrialized countries, the prevalence of alveolar echinococcosis (AE) did not decrease. [4] On the contrary, incidents of AE have now also been registered in eastern European countries and sporadic incidences in other European countries. [4]

The disease has extended its range in Europe in the last few decades. [15] Still the infection is fairly rare. Between 1982 and 2000 a total of 559 cases were reported throughout Europe. [16]

Recent findings indicate that E. multilocularis is likely expanding its range in the central region of the United States and Canada and that invasions of European strains might have occurred; the endemic presence of the parasite in urban areas and a total of 16 human cases in Alberta, Canada have been reported. [13] [17] The first human case in Alberta was diagnosed in 2013. In one case, the infection caused a grapefruit sized tumour in the lung, kidney and diaphragm, which had to be surgically removed. [17] Because of the significant difficulty in diagnosising an infection caused by Echinococcus multiocularis, it is suspected that this parasite if often misdiagnosed. Several studies that have been done since the 1950s in North America indicate a higher prevalence of Echinococcus multiocularis than previously thought. However, due to limited knowledge about the parasite, it is often not monitored in wild or domestic animals; this monitoring will become crucial to the control of the parasite in the future as it continues to spread. [13]

See also

Related Research Articles

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Echinococcosis is a parasitic disease of 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.

<span class="mw-page-title-main">Albendazole</span> Chemical compound

Albendazole is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trichuriasis, strongyloidiasis, taeniasis, clonorchiasis, opisthorchiasis, cutaneous larva migrans, giardiasis, and gnathostomiasis, among other diseases.

<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>Echinococcus</i> Genus of worms

Echinococcus is a genus within Cestoda, a parasitic class of the platyhelminthes phylum. Human echinococcosis is an infectious disease caused by the following species: E. granulosus, E. multilocularis, or E. vogeli.

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

Echinococcus granulosus, also called the hydatid worm, hyper tape-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>Dipylidium caninum</i> Species of flatworm

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.

<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">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.

Spirometra erinaceieuropaei is a parasitic tapeworm that infects domestic animals and humans. The medical term for this infection in humans and other animals is sparganosis. Morphologically, these worms are similar to other worms in the genus Spirometra. They have a long body consisting of three sections: the scolex, the neck, and the strobilia. They have a complex life cycle that consists of three hosts, and can live in varying environments and bodily tissues. Humans can contract this parasite in three main ways. Historically, humans are considered a paratenic host; however, the first case of an adult S. erinaceieuropaei infection in humans was reported in 2017. Spirometra tapeworms exist worldwide and infection is common in animals, but S. erinaceieuropaei infections are rare in humans. Treatment for infection typically includes surgical removal and anti-worm medication.

<i>Capillaria hepatica</i> Species of roundworm

Capillaria hepatica is a parasitic nematode which causes hepatic capillariasis in rodents and numerous other mammal species, including humans. The life cycle of C. hepatica may be completed in a single host species. However, the eggs, which are laid in the liver, must mature outside of the host body prior to infecting a new host. So the death of the host in which the adults reach sexual maturity, either by being eaten or dying and decomposing, is necessary for completion of the life cycle.

<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.

<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.

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

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<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.

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