''Crithidia fasciculata'' is a species of

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

excavates. ''C. fasciculata'', like other species of ''

Crithidia ''Crithidia'' is a genus of trypanosomatid Euglenozoa. They are parasites that exclusively parasitise arthropods, mainly insects. They pass from host to host as cysts in infective faeces and typically, the parasites develop in the digestive trac ...

'' have a single host life cycle with

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

host, in the case of ''C. fasciculata'' this is the

mosquito Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...

. ''C. fasciculata'' have low host species specificity and can infect many species of mosquito.

Life cycle

''C. fasciculata'' is found in two morphologically different life cycle stages – the free swimming choanomastigote form, which has a long external

flagellum A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

for motility, and the attached, immotile,

amastigote An amastigote is a protist cell that does not have visible external flagella or cilia. The term is used mainly to describe an intracellular phase in the life-cycle of trypanosomes that replicates. It is also called the leishmanial stage, since in ...

form in the mosquito gut. Amastigotes excreted in the

faeces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...

contaminate the mosquito habitat; contamination of flowers during

nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

feeding is common. Transmission of ''C fasciculata'' primarily occurs when amastigotes, washed into standing water, are ingested by mosquito

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

. The amastigotes are typically found in the rectum of a larva. Each molt of the larva results in loss of infection, but it is generally quickly re-acquired from the environment by ingestion of more amastigotes. When the fourth instar larva

pupa A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

tes the amastigote infection is maintained in the gut through

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

giving rise to an infected adult mosquito.

Role in research

''C. fasciculata'' is an example of a non-human infective

trypanosomatid Trypanosomatida is a group of kinetoplastid unicellular organisms distinguished by having only a single flagellum. The name is derived from the Greek ''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of some trypanosoma ...

and is related to several human parasites, including ''

Trypanosoma brucei ''Trypanosoma brucei'' is a species of parasitic Kinetoplastida, kinetoplastid belonging to the genus ''Trypanosoma'' that is present in sub-Saharan Africa. Unlike other protozoan parasites that normally infect blood and tissue cells, it is excl ...

'' (which causes

African trypanosomiasis African trypanosomiasis is an insect-borne parasitic infection of humans and other animals. Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species ''Trypanosoma bru ...

) and ''

Leishmania ''Leishmania'' () is a genus of parasitic protozoans, single-celled eukaryotic organisms of the trypanosomatid group that are responsible for the disease leishmaniasis. The parasites are transmitted by sandflies of the genus '' Phlebotomus'' ...

'' spp. (which cause

Leishmaniasis Leishmaniasis is a wide array of clinical manifestations caused by protozoal parasites of the Trypanosomatida genus ''Leishmania''. It is generally spread through the bite of Phlebotominae, phlebotomine Sandfly, sandflies, ''Phlebotomus'' an ...

). ''C. fasciculata'' parasitizes several species of insects and has been widely used to test new therapeutic strategies against parasitic infections. ''C. fasciculata'' is often used as a model organism in research into trypanosomatid biology that may then be applied to understanding the biology of the human infective species. As is typical of the trypanosomatids, but unlike many other protists, ''C. fasciculata'' possess one mitochondrion. The mitochondrial DNA is found in a single structure, the

kinetoplast A kinetoplast is a network of circular DNA (called kDNA) inside a mitochondrion that contains many copies of the mitochondrial genome. The most common kinetoplast structure is a disk, but they have been observed in other arrangements. Kinetoplasts ...

, at the base of the single flagellum. As is common with parasitic species ''C. fasciculata'' requires a high nutrient content broth (including heme and folic acid) in which to grow under laboratory conditions.

Life cycle

Role in research

References

Further reading