Castellanella Chalmers 1918 non Pacheco & Rodrigues 1930
Duttonella Chalmers 1918
Haematomonas Mitrophanow 1883
Schizotrypanum Chagas 1909
Trypanozoon Lühe 1906
Trypanosoma is a genus of kinetoplastids (class Trypanosomatidae), a group of unicellular parasiticflagellateprotozoa under the phylum Euglenozoa. The name is derived from the Ancient Greektrypano- (borer) and soma (body) because of their corkscrew-like motion. Most trypanosomes are heteroxenous (requiring more than one obligatory host to complete life cycle) and most are transmitted via a vector. The majority of species are transmitted by blood-feeding invertebrates, but there are different mechanisms among the varying species. Trypanosoma equiperdum is spread between horses and other equine species by sexual contact. They are generally found in the intestine of their invertebrate host, but normally occupy the bloodstream or an intracellular environment in the vertebrate host.
The mitochondrial genome of the Trypanosoma, as well as of other kinetoplastids, known as the kinetoplast, is made up of a highly complex series of catenated circles and minicircles and requires a cohort of proteins for organisation during cell division.
Many past phylogenetic analyses using the 18S (small subunit) ribosomal RNA (SSU rRNA) sequence have indicated a non-monophyleticTrypanosoma (as "traditionally defined") with the biflagellate Bodonida nested within. These methods suggest an ancient split between a branch containing all Salivarian trypanosomes and a branch containing all non-Salivarian lineages. The latter branch in turn splits into a clade containing bird, reptilian and the Stercorarian trypanosomes infecting mammals, and a clade with a branch of fish trypanosomes and a branch of reptilian or amphibian lineages.
However, analyses using both the combination of the glyceraldehyde phosphate dehydrogenase gene with SSU rRNA, of whole genomes, and of the kinetoplast (mitochondrial) genome indicate that Trypanosoma (again, as "traditionally defined") is, indeed, monophyletic. This is in spite of the distinctness of the clades formed by T. cruzi (cause of Chagas' disease) and T. brucei (cause of African sleeping sickness). The division into the Salivaria and the Stercoria remains valid as each can be assigned to a clade in these analyses.
Group Salivaria: African trypanosomes, passed to the vertebrate recipient in the saliva of the tsetse fly (Glossina spp.). Antigenic variation is a characteristic shared by the Salivaria, which has been particularly well-studied in T. brucei.
Group Stercoraria: Central/South American trypanosomes, passed to the vertebrate recipient in the feces of insects from the subfamily Triatominae (most importantly Triatoma infestans). Some subgenera are:
Subgenus Herpetosoma, which contains T. lewisi and T. rangeli (inclusion of both species would make the subgenus paraphyletic)
Evolution
The overall evolution of the group follows the general structure of the groups and subgenera. Of interest is how the trypanosomes became parasistic in the first place, how it became dixenous (parasitizes two hosts), and how it came to affect vertebrates, mammals, and then humans in particular. The emergence of parasitism is dated back to the origin of the order Trypanosomatida, which includes both the trypanosomes and the Leishmania; Bodo saltans is a reasonably close relative to the common ancestor of this group. The emergence of a dixenous lifestyle from a monoxenous ancestor has happened at least three times, in Phytomonas, in vertebrate-infecting Trypanosoma, and in vertebrate-infecting Leishmania/Porcisia/Endotrypanum.
The Salivaria split from the rest of the trypanosomes about 150 million years ago (Mya). They were probably mainly living in the guts of insects, until the appearance of tsetse flies gave them access to mammalian blood. On the other hand, the common ancestor of the T. cruzi clade (~Schizotrypanum) appeared about 84 million years ago, not long before the diversification of bats, which is thought to have contributed to the diversification of the group and ultimately a trypanosome that infects many different types of mammals.
T. brucei evansi, which causes one form of the disease surra in certain animals including camels (a single case report of human infection in 2005 in India was successfully treated with suramin.). Enmerged at two independent occasions in Western Africa.
T. brucei gambiense and T. brucei rhodesiense, both of which cause sleeping sickness in humans.
Two different types of trypanosomes exist, and their life cycles are different, the salivarian species and the stercorarian species.[citation needed]
Stercorarian trypanosomes infect insects, most often the triatomid kissing bug, by developing in the posterior gut followed by release into the feces and subsequent depositing on the skin of the vertebrate host. The organism then penetrates and can disseminate throughout the body. Insects become infected when taking a blood meal.[citation needed]
Salivarian trypanosomes develop in the anterior gut of insects, most importantly the Tsetse fly, and infective organisms are inoculated into the host by the insect bite before it feeds.[citation needed]
As trypanosomes progress through their life cycle they undergo a series of morphological changes as is typical of trypanosomatids. The life cycle often consists of the trypomastigote form in the vertebrate host and the trypomastigote or promastigote form in the gut of the invertebrate host. Intracellular lifecycle stages are normally found in the amastigote form. The trypomastigote morphology is unique to species in the genus Trypanosoma.[citation needed]
Meiosis
Evidence has been obtained for meiosis in T. cruzi, and for genetic exchange. T. brucei is able to undergo meiosis within the salivary glands of its tsetse fly host, and meiosis is considered to be an intrinsic part of the T. brucei developmental cycle. An adaptive benefit of meiosis for T. crucei and T. brucei may be the recombinational repair of DNA damages that are acquired in the hostile environment of their respective hosts.
↑Leadbeater, B.S.C & McCready, S.M.M. (2000). The Flagellates. Unity, diversity and evolution. Ed.: Barry S. C. Leadbeater and J. C. Green Taylor and Francis, London, p. 12.
↑Gruby, D. 1843. Recherches et observations sur une nouvelle espéce d'haematozoaire, Trypanosoma sanguinis. Comptes Rendus de l'Académie des Sciences, 17: 1134–1136, .
↑Haag, J.; O'Huigin, C.; Overath, P. (1998). "The molecular phylogeny of trypanosomes: Evidence for an early divergence of the Salivaria". Molecular and Biochemical Parasitology. 91 (1): 37–49. doi:10.1016/S0166-6851(97)00185-0. PMID9574924.
↑Piontkivska, Helen; Hughes, Austin L. (2005). "Environmental kinetoplastid-like 18S rRNA sequences and phylogenetic relationships among Trypanosomatidae: Paraphyly of the genus Trypanosoma". Molecular and Biochemical Parasitology. 144 (1): 94–99. doi:10.1016/j.molbiopara.2005.08.007. PMID16169099.
↑Hamilton PB, Stevens JR, Gaunt MW, Gidley J, Gibson WC (2004). "Trypanosomes are monophyletic: evidence from genes for glyceraldehyde phosphate dehydrogenase and small subunit ribosomal RNA". Int. J. Parasitol. 34 (12): 1393–404. doi:10.1016/j.ijpara.2004.08.011. PMID15542100.
↑Leonard, G; Soanes, DM; Stevens, JR (July 2011). "Resolving the question of trypanosome monophyly: a comparative genomics approach using whole genome data sets with low taxon sampling". Infection, Genetics and Evolution: Journal of Molecular Epidemiology and Evolutionary Genetics in Infectious Diseases. 11 (5): 955–9. Bibcode:2011InfGE..11..955L. doi:10.1016/j.meegid.2011.03.005. PMID21419879.
↑Deschamps, P.; Lara, E.; Marande, W.; Lopez-Garcia, P.; Ekelund, F.; Moreira, D. (1 January 2011). "Phylogenomic Analysis of Kinetoplastids Supports That Trypanosomatids Arose from within Bodonids". Molecular Biology and Evolution. 28 (1): 53–58. doi:10.1093/molbev/msq289. PMID21030427.
↑World Health, Organization (2005). "A new form of human trypanosomiasis in India. Description of the first human case in the world caused by Trypanosoma evansi". Wkly. Epidemiol. Rec. 80 (7): 62–3. PMID15771199.
↑Joshi PP, Chaudhari A, Shegokar VR, etal. (2006). "Treatment and follow-up of the first case of human trypanosomiasis caused by Trypanosoma evansi in India". Trans. R. Soc. Trop. Med. Hyg. 100 (10): 989–91. doi:10.1016/j.trstmh.2005.11.003. PMID16455122.
