Kinetoplastid

The kinetoplastids are a group of flagellate protozoa, including a number of parasites responsible for serious diseases in humans and other animals, as well as various forms found in soil and aquatic environments. They are included in the Euglenozoa, and are distinguished from other such forms mainly by the presence of a kinetoplast, a DNA-containing granule located within the single mitochondrion and associated with the flagellar bases.

Most forms have a leading and trailing flagellum, the latter of which may or may not be attached to the side of the cell and is often used to glide along or attach to surfaces. The cytostome is often bordered by a ridge or rostrum. Bodo is a typical genus, including various common free-living species which feed on bacteria. Others include Cryptobia and Trypanoplasma. There is also one family of kinetoplastids, the trypanosomes, which only have a single emergent flagellum, including several genera which are exclusively parasitic.

Trypanosomes have reduced or absent cytostomes, feeding entirely through absorption, and smaller kinetoplasts than other forms. They typically have complex life-cycles involving more than one host, and go through various morphological stages. The most distinctive of these is the trypanosome stage, where the flagellum runs along the length of the cell and is connected to it by an undulating membrane. Diseases caused by trypanosomes include sleeping sickness and Chagas disease, from species of Trypanosoma, and leishmaniasis, from species of Leishmania.

The kinetoplastids were first defined by Honigberg in 1961 as the flagellate order Kinetoplastida. They are traditionally divided into the biflagellate Bodonidae and uniflagellate Trypanosomatidae, which may be promoted to orders; the former appears to be paraphyletic to the latter.