Hymenolepis microstoma

Last updated

Hymenolepis microstoma
Hymenolepis microstoma.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Cestoda
Order: Cyclophyllidea
Family: Hymenolepididae
Genus: Hymenolepis
Species:
H. microstoma
Binomial name
Hymenolepis microstoma
Dujardin, 1845
Synonyms [1]
  • Vampirolepis microstoma
    (Dujardin, 1854) Spasskii, 1954
  • Rodentolepis microstoma
    (Dujardin, 1854) Spasskii, 1954
  • Taenia microstoma
    Dujardin, 1845
  • Taenia brachydera
    Diesing, 1854
  • Taenia murisdecumani
    Diesing, 1863

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. [2]

Contents

Ecology

Hymenolepis microstoma is an obligate parasite. Adults live in the bile duct and small intestine of rodents such as mice ( Mus musculus ), and larvae infect grain beetles such as Tribolium spp., in which they metamorphose from larvae into juvenile worms. [3] Worms vary from 4 to 30 cm in length, depending on the age and number of worms within the host. [3] Adults have completely lost their mouth and intestine. Instead they use their skin (tegument) to absorb nutrients directly from the host gut. [3]

Hymenolepis species and other tapeworms often exhibit a 'crowding effect' in which the total biomass of the worms stays more or less constant, regardless of the intensity of infection. Thus low intensity infections result in larger worms and high intensity infections produce smaller worms. Under laboratory conditions, H. microstoma adult infections in mice are typically limited to approximately 12 worms. [3]

Life cycle

The cycle begins as arthropods become intermediate hosts by ingesting the parasite eggs. Oncospheral larvae are released from the eggs and use hooks and secreted enzymes to penetrate the gut of the beetles and enter the haemocoel. In the haemocoel the larvae undergo complete cellular reorganization (i.e. metamorphosis), transforming into cysticercoid larvae in approximately 7–10 days. The larvae can remain in the cysticercoid stage in the beetle as long as the lifespan of the adult beetle (up to 3 years), although any age-related decrease in viability has not been studied. [3] When ingested, the eggs develop into cysticercoids. Rodents can become infected when they eat arthropods, such as flour beetles ( Tribolium ssp). Humans, especially children, can ingest the arthropods as well and therefore become infected via the same mechanism. Rodents, especially rats, are definitive hosts and natural reservoirs of H. microstoma. As the definitive host (rats) eats an infected arthropod, cysticercoids present in the body cavity transform into the adult worm. Juvenile worms establish in the bile duct of mice after approximately 3 days movement within the upper gastrointestinal tract. Once established in the bile duct, the worms then mature sexually and begin producing eggs within approximately 1 week. [3] Eggs are released with mouse faeces and thus dispersal is passive - through the movement and defecation of mice. Adult worm infections in mice held under laboratory conditions persist for 6–12 months.

Worms reproduce sexually via the cross fertilization of segments, each of which contains a complete complement of male and female reproductive organs (hermaphroditic). Shelled embryos develop in the ovaries through spiral cleavage, to become infective larvae with 3 pairs of hooks. When ingested by beetles, these larvae use their hooks and secretory glands to penetrate the gut of the beetle and enter the haemocoel where they undergo complete metamorphosis into cysticercoid larvae, replete with an adult scolex, ready for establishment in the final host. [3]

Cytology

Like all flatworms (phylum Platyhelminthes), H. microstoma maintains totipotent stem cells (called neoblasts in flatworms) throughout its life cycle. These are located in the neck region of the adult worms and are responsible for the continual production of new organs during the process of strobilation (segment formation). [1] [4] Neoblasts divide in the neck region and become incorporated into new segments where they eventually differentiate into the reproductive organs and other elements of the body. [4] The diploid chromosome number of H. microstoma is 12 and the total genome size has been estimated by the Sanger Institute to be 1.4 megabases (with GC-content of ~35%). [1] [5] These values are similar to the genomes of the fox tapeworm Echinococcus multilocularis and the pig tapeworm Taenia solium . [6] All three species belonging to the tapeworm order Cyclophyllidea. Genome sizes outside of this order are presently unknown. [4]

Evolution

The parasitic flatworms, which includes tapeworms, flukes and monogeneans, evolved from a single major lineage of free-living flatworm ancestors. The switch from a free-living to a parasitic lifestyle in the common ancestor of the parasitic flatworms involved a fundamental change in their tegument, which is found in all contemporary groups. [7] Early-branching tapeworm groups are found in bony (e.g. teleost) and cartilaginous fishes (e.g. sharks and rays) and have entirely aquatic life cycles involving arthropod (e.g. copepods) first intermediate hosts and vertebrate (fish) final hosts. Tetrapod hosts (including mice and humans) were acquired later in tapeworm evolution and eventually part-aquatic life cycles led to the evolution of fully terrestrial life cycles, albeit still involving an arthropod intermediate host and a vertebrate definitive host. [7] Hymenolepis microstoma is a member of the Cyclophyllidea, one of the youngest and most species-rich group of tapeworms. [7]

Research impact

Most of our understanding of the basic biology of tapeworms, such as their anatomy, physiology and ultrastructure, stems from work on this genus. [7] Species in the genus Hymenolepis (e.g. H. diminuta , H. microstoma, H. nana ) have been maintained as laboratory models for studying tapeworm biology since the 1950s. [7] They can be readily maintained in vivo in rodent and beetle hosts, which makes them useful for teaching and research purposes. They can also be grown in culture ( in vitro ), giving easy manipulation of the life cycle..

Infection and treatment

Hymenolepis microstoma primarily infects rodents, and is only very rarely found in humans. Human H. microstoma infection is often asymptomatic, but abdominal pain, irritability, itching, and eosinophilia are among the existing symptoms in a few of the reported cases. Since data regarding praziquantel treatment of H. microstoma is sparse, scientists have recommended that every case and treatment of H. microstoma be reported for development of protocols and parasitological purposes.

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.

<i>Diphyllobothrium</i> Genus of flatworms

Diphyllobothrium is a genus of tapeworms which can cause diphyllobothriasis in humans through consumption of raw or undercooked fish. The principal species causing diphyllobothriasis is D. latum, known as the broad or fish tapeworm, or broad fish tapeworm. D. latum is a pseudophyllid cestode that infects fish and mammals. D. latum is native to Scandinavia, western Russia, and the Baltics, though it is now also present in North America, especially the Pacific Northwest. In Far East Russia, D. klebanovskii, having Pacific salmon as its second intermediate host, was identified.

Hymenolepiasis is infestation by one of two species of tapeworm: Hymenolepis nana or H. diminuta. Alternative names are dwarf tapeworm infection and rat tapeworm infection. The disease is a type of helminthiasis which is classified as a neglected tropical disease.

<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.

<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.

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

The Hymenolepididae are family of cyclophyllid tapeworms. Their characteristic feature is the small number of testes. The unilateral genital pores and large external seminal vesicle allow for easy recognition. Most species are small, transparent, and easy to study. The family contains over 90 genera with over 900 species, having as their definitive host birds or mammals. Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have arthropods as intermediate hosts.

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

Dwarf tapeworm is a cosmopolitan species though most common in temperate zones, and is one of the most common cestodes infecting humans, especially children.

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

Hymenolepis diminuta, also known as rat tapeworm, is a species of Hymenolepis tapeworm that causes hymenolepiasis. It has slightly bigger eggs and proglottids than H. nana and infects mammals using insects as intermediate hosts. The adult structure is 20 to 60 cm long and the mature proglottid is similar to that of H. nana, except it is larger.

<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>Hymenolepis</i> (flatworm) Genus of worms

Hymenolepis is a genus of cyclophyllid tapeworms that cause hymenolepiasis. They parasitise mammals, including humans. Some notable species are:

<i>Toxascaris leonina</i> Species of roundworm

Toxascaris leonina is a common parasitic roundworm found in dogs, cats, foxes, and related host species. T. leonina is an ascarid nematode, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as lice and fleas, live inside their host. The definitive hosts of T. leonina include canids and felines (cats), while the intermediate hosts are usually rodents, such as mice or rats. Infection occurs in the definitive host when the animal eats an infected rodent. While T. leonina can occur in either dogs or cats, it is far more frequent in cats.

<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.

Bertielliasis is the infection of Bertiella, a cestode tapeworm parasite that primarily infects nonhuman primates, rodents and Australian marsupials. Occasionally, human infections have been documented by one of two species: Bertiella studeri, or Bertiella mucronata. Of 29 different Bertiella species, only these two can infect humans.

<i>Raillietina</i> Genus of flatworms

Raillietina is a genus of tapeworms that includes helminth parasites of vertebrates, mostly of birds. The genus was named in 1920 in honour of a French veterinarian and helminthologist, Louis-Joseph Alcide Railliet. Of the 37 species recorded under the genus, Raillietina demerariensis, R. asiatica, and R. formsana are the only species reported from humans, while the rest are found in birds. R. echinobothrida, R. tetragona, and R. cesticillus are the most important species in terms of prevalence and pathogenicity among wild and domestic birds.

Raillietina cesticillus is a parasitic tapeworm of the family Davaineidae. Sometimes called "Broad-headed tapeworm", it infects the small intestine of chicken and occasionally other birds, such as guinea fowl and turkey, which are generally in close proximity to backyard poultry. It is a relatively harmless species among intestinal cestodes in spite of a high prevalence. In fact it probably is the most common parasitic platyhelminth in modern poultry facilities throughout the world.

Bertiella mucronata is a species of Bertiella, a type of cestode tapeworms known to cause Bertielliasis. It belongs to the genus Bertiella, family Anoplocephalidae. This is one of two species of Bertiella that can cause the condition in humans.

Pterygodermatites peromysci is an intestinal parasitic nematode in the genus Pterygodermatites of the family Rictulariidae.

<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. 1 2 3 Cunningham LJ, Olson PD (2010). "Description of Hymenolepis microstoma (Nottingham strain): a classical tapeworm model for research in the genomic era". Parasit Vectors. 3: 123. doi: 10.1186/1756-3305-3-123 . PMC   3023764 . PMID   21194465.
  2. Macnish MG, Ryan UM, Behnke JM, Thompson RC (September 2003). "Detection of the rodent tapeworm Rodentolepis (=Hymenolepis) microstoma in humans. A new zoonosis?". Int. J. Parasitol. 33 (10): 1079–85. doi:10.1016/s0020-7519(03)00137-1. PMID   13129530.
  3. 1 2 3 4 5 6 7 Olson lab website, Dept. of Zoology, Natural History Museum, London
  4. 1 2 3 Olson PD (March 2008). "Hox genes and the parasitic flatworms: new opportunities, challenges and lessons from the free-living". Parasitol. Int. 57 (1): 8–17. doi:10.1016/j.parint.2007.09.007. PMID   17977060.
  5. Hymenolepis microstoma. Wellcome Trust Sanger Institute. Retrieved 1 February 2011.
  6. Echinococcus multilocularis. Wellcome Trust Sanger Institute. Retrieved 1 February 2011.
  7. 1 2 3 4 5 Olson PD, Littlewood DT, Bray RA, Mariaux J (June 2001). "Interrelationships and evolution of the tapeworms (Platyhelminthes: Cestoda)". Mol. Phylogenet. Evol. 19 (3): 443–67. doi:10.1006/mpev.2001.0930. PMID   11399152.