''Crithidia'' is a genus of
trypanosomatid
Trypanosomatida is a group of kinetoplastid excavates 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 trypanosomatid species ...
Euglenozoa. They are
parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
that exclusively parasitise
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s, mainly insects. They pass from host to host as cysts in infective
faeces
Feces ( or faeces), known colloquially and in slang as poo and poop, 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 large intestine. Feces contain a relati ...
and typically, the parasites develop in the digestive tracts of insects and interact with the intestinal
epithelium using their
flagellum
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
. They display very low host-specificity and a single parasite can infect a large range of invertebrate hosts. At different points in its life-cycle, it passes through
amastigote
An amastigote is a protist
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryot ...
,
promastigote
Trypanosomatida is a group of kinetoplastid excavates 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 trypanosomatid species. ...
, and epimastigote phases; the last is particularly characteristic, and similar stages in other trypanosomes are often called crithidial.
The
etymology
Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...
of the genus name ''Crithidia'' derives from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
word (), meaning "small grain of barley".
Species
* ''
Crithidia bombi'' is perhaps the most well documented species and is the most prevalent parasite of
bumblebee
A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related genera ...
s, including common species like ''
Bombus terrestris
''Bombus terrestris'', the buff-tailed bumblebee or large earth bumblebee, is one of the most numerous bumblebee species in Europe. It is one of the main species used in greenhouse pollination, and so can be found in many countries and areas wher ...
'', ''
Bombus muscorum'', and ''
Bombus hortorum
''Bombus hortorum'', the garden bumblebee or small garden bumblebee, is a species of bumblebee found in most of Europe north to 70°N, as well as parts of Asia and New Zealand. It is distinguished from most other bumblebees by its long tongue ...
''.
The parasites negatively impact reproductive fitness of ''Bombus'' queens, as they affect their ovarian development as well as early colony establishment after the queens emerge from hibernation.
* ''
Crithidia mellificae'' is a parasite of the
bee.
* ''
Crithidia brevicula'' might incorporate species of the genus ''
Wallaceina'' (''Wallaceina brevicula'', ''W. inconstans'', ''W. vicina'', and ''W. podlipaevi'') as suggested by molecular phylogenies based on
18S ribosomal RNA
18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA. The S in 18S represents Svedberg units. 18S rRNA is an SSU rRNA, a component of the eukaryotic ribosomal small subunit ( 40S). 18S rRNA is the structural RNA for the small ...
and
glycosomal glyceraldehyde-3-phosphatedehydrogenase sequences.
* Other species include ''
C. fasciculata'', ''
C. deanei'', ''
C. desouzai'', ''
C. oncopelti'', ''
C. guilhermei'' and ''
C. luciliae''.
* ''C. deanei'' is atypical of the ''Crithidia'' genus, and it has been argued not a member of the ''Crithidia'' at all. It is not typical of trypanosomatids because of its unusual shape and it harbours
endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
bacteria. ''C. luciliae'' is the substrate for the
antinuclear antibody test used to diagnose lupus and other autoimmune disorders
Impact on bumble bees
These parasites may be at least partially responsible for declining wild bumble bee populations. They cause the bumble bees to lose their ability to distinguish between flowers that contain
nectar and those that don't. They make many mistakes by visiting nectar scarce flowers and in so doing, slowly starve to death. Commercially bred bumble bees are used in greenhouses to pollinate plants, for example tomatoes, and these bumble bees typically harbor the parasite, while wild bumble bees do not. It is believed that the commercial bumble bees transmitted the parasite to wild populations in some cases. They escape from the greenhouses through vents; a simple mesh could help prevent this.
Bibliography
Further reading
External links
{{Taxonbar, from=Q1998692
Trypanosomatida
Parasitic excavates
Euglenozoa genera