__NOTOC__ The Hymenolepididae are

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

cyclophyllid Cyclophyllidea (the cyclophyllid cestodes) is the order (biology), order of Cestoda, Cestoda (tapeworm). It is the largest and most diverse order of Cestoda (tapeworm), encompassing species that infect all classes of terrestrial Tetrapod, tetrapo ...

tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass being Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Ce ...

s. Their characteristic feature is the small number of

testes A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The ...

(one to four). The unilateral genital pores and large external

seminal vesicle The seminal vesicles (also called vesicular glands or seminal glands) are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen. The vesicles are 5 ...

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 In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

birds (c. 700 species) or mammals (about 250 species). Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

intermediate hosts In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include a ...

As human parasites

The family Hymenolepididae has only two species which infects humans: the disease

hymenolepiasis 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 ...

is caused by ''

Hymenolepis nana Dwarf tapeworm (''Hymenolepis nana'', also known as ''Rodentolepis nana'', ''Vampirolepis nana'', ''Hymenolepis fraterna'', and ''Taenia nana'') is a cosmopolitan species though most common in temperate zones, and is one of the most common ces ...

'' and '' H. diminuta'', which are sometimes classified in the genus ''Rodentolepis''. Most cases of hymenolepiasis are caused by ''H. nana''. It occurs worldwide, but in temperate climates, children and people living in institutions are more likely to be infected. A morphologically-identical variety of ''H. nana'', ''H. nana'' var. ''fraterna'' infects

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s, but the human strain of ''H. nana'' is essentially non-infective to rodents. Unlike most tapeworms, including ''H. diminuta'', ''H. nana'' can complete its lifecycle without an intermediate host. Pathological effects of infection are rare and occur in massive infections through autoinfection, where the parasite is able to complete its lifecycle within the intestine of the human host, without passing through an intermediate host outside the body. With increasing worm burden, symptoms such as restlessness, irritability, diarrhea, and abdominal pain occur. ''H. diminuta'' is primarily a parasite of

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...

s, but human infections occur as incidental hosts. It is a larger species than ''H. nana'' and lacks hooks on the

rostellum The rostellum is a projecting part of the column in Orchidaceae flowers, and separates the male androecium from the female gynoecium, commonly preventing self-fertilisation. In many orchids, such as '' Orchis mascula'', the pollinia or pollen m ...

; it has three testes per

proglottid Cestoda is a Class (biology), 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, commonly known as tapeworms. T ...

. Species from a diverse set of

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

taxa, including earwigs, butterflies, and beetles, can be

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

s for this species, which is unusual for a tapeworm. Grain beetles are common intermediate hosts, because they live in piles of grain where they can be ingested by rats, which are the definitive hosts. Drugs commonly used for treatment of hymenolepiasis are

praziquantel Praziquantel, 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 schist ...

niclosamide Niclosamide, sold under the brand name Niclocide among others, is an anthelmintic medication used to treat tapeworm infestations, including diphyllobothriasis, hymenolepiasis, and taeniasis. It is not effective against other worms such as ...

, and

paromomycin Paromomycin is an antimicrobial used to treat a number of parasitic infections including amebiasis, giardiasis, leishmaniasis, and tapeworm infection. It is a first-line treatment for amebiasis or giardiasis during pregnancy. Otherwise, it ...

Selected genera

* '' Allohymenolepis'' * '' Amphipetrovia'' * '' Aploparaxis'' * '' Armadolepis'' * '' Brachylepis'' * '' Branchiopodataenia'' * '' Cladogynia'' * '' Cloacotaenia'' * '' Colibrilepis'' * '' Confluaria'' * '' Coronacanthus'' * '' Dicranotaenia'' * '' Dildotaenia'' * '' Diorchis'' * '' Diploposthe'' * '' Dollfusilepis'' * '' Drepanidotaenia'' * '' Echinolepis'' * '' Fimbriaria'' * '' Flamingolepis'' * '' Hilmylepis'' * '' Hsuolepis'' * '' Hymenolepis'' (sometimes included in ''Rodentolepis'') * '' Mathevolepis'' * '' Passerilepis'' * '' Potorolepis'' * '' Pseudhymenolepis'' * '' Retinometra'' * '' Rodentolepis'' * '' Soricinia'' * '' Staphylocystis'' * '' Triodontolepis'' * '' Vampirolepis'' * '' Variolepis'' * '' Wardium''

References

Cestoda Platyhelminthes families {{Cestoda-stub