Trypanosoma is a genus of kinetoplastids (class Trypanosomatidae), a group of unicellular parasitic flagellate protozoa under the phylum Euglenozoa. The name is derived from the Ancient Greek trypano- (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. Trypanosomes infect a variety of hosts and cause various diseases, including the fatal human diseases sleeping sickness, caused by Trypanosoma brucei, and Chagas disease, caused by Trypanosoma cruzi. 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.
History In 1841, Gabriel Valentin found flagellates that today are included in Trypanoplasma in the blood of trout. The genus (T. sanguinis) was named by Gruby in 1843, after parasites in the blood of frogs. In 1903, David Bruce identified the protozoan parasite and the tsetse fly vector of African trypanosomiasis.
Taxonomy Many past phylogenetic analyses using the 18S (small subunit) ribosomal RNA (SSU rRNA) sequence have indicated a non-monophyletic Trypanosoma (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. Subgenus Trypanozoon includes T. brucei, T. rhodesiense, etc. Subgenus Duttonella includes T. vivax. Subgenus Nannomonas contains T. congolense. 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 Schizotrypanum, which contains T. cruzi and a number of bat trypanosomes. The bat species include T. cruzi marinkellei (a subspecies of T. cruzi), T. dionisii, T. erneyi, T. livingstonei and T. wauwau. There are a few species yet unnamed. 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.
Selected species Species of Trypanosoma include the following:
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