Chilomastix

The nomenclature of this genus has been under much dispute throughout history, switching between many different taxonomic names. The first known report of this genus was in 1854 when patients in Paris showed infection by a parasitic flagellate. The human parasite was classified under the name of Cercomonas hominis var. 1 by Davaine (1854). In 1910, it was reclassified as its own species and named Macrostoma mesnili by Charles Morley Wenyon, an English protozoologist. It was again renamed to Chilomastix davainei (syn. Chilomastix mesnili) in 1920 by Kofoid. The origin of the name Chilomastix however, was before 1920. The initial proposal of Chilomastix being its own genus was urged by Alexeieffe in 1912 who was the first to thoroughly describe a species belonging to this genus. Although he initially called it Tetramitus caulleryi in 1910, he then referred it is as its own genus, Chilomastix in 1912. ==Habitat and ecology==

Geographical distribution Chilomastix has a worldwide distribution; Chilomastix mesnili is considered a cosmopolitan species, having been found in marine, freshwater and brackish waters. This genus, however, is more prevalent in warmer climates. Microenvironment The cyst stage of the organism if often found in feces where it can thrive away from a host, until it is ingested. Bird hosts, as seen in ostriches, rheas, chickens and geese, as well as invertebrate hosts such as insects have also been documented. ==Life cycle==

The life cycle is direct, requiring no intermediate host or vector. Once the intestinal contents begin to dry out, the trophozoites then release a cyst wall through the process of encystation. Cysts are resistant and do not require feeding to survive, thus once the food source begins to run out, stimulation of encystation occurs. Both trophozoites and cysts are passed in the feces but only cysts can survive outside of the host and are therefore the stage of infection. When exposed to the external environment, the trophozoites disintegrate while the cysts remain living in bodies of water until they are again taken up by the next host, continuing the cycle of transmission. ==Feeding mechanisms==

Within the intestine of the host, Chilomastix trophozoites feed via endocytosis. This brings the particles into the cell and stimulates the formation of a food vacuole. Chilomastix often feeds on bacteria living inside the gut of the host. The cytosomal flagellum aids in bringing intestinal bacteria closer towards the cell, allowing the membrane to wrap around the food particle and pinch off to form a food vacuole within the cell body. The cyst stage is non-feeding. ==Pathogenesis==

Chilomastix species are generally regarded as harmless gut commensals and are non-pathogenic. Diagnosis Chilomastix species are often transmitted along with other intestinal parasites, many of which are pathogenic and do cause diseases such as Giardia lamblia and Balantidium coli. This commonly causes confusion during diagnosis. Diagnosis is made upon finding one or both cyst and trophozoite forms in feces samples of an infected patient. Treatment Due to the non-pathogenic nature of this taxon, no treatments are required except to relieve the discomfort of the diarrhea in extreme cases. If the infected patient is showing other symptoms of disease, it is most likely due to the presence of another parasitic pathogen and further testing should be done. ==Morphology and anatomy==

Chilomastix cells are not bilaterally symmetrical and lack mitochondria, an axostyle, Golgi apparatus, and an undulating membrane. Trophozoites Trophozoites of Chilomastix have been described as pyriform, lemon-shaped or pear-shaped in various species with a rounded anterior and an elongated posterior end that comes to a point. Four flagella are present in all species; three flagella extend anteriorly and move freely, while the fourth flagellum is located within the feeding groove that acts as the cell mouth. This fourth, posteriorly orientated flagellum is vaned, due to the presence of two wing-like structures that extend from it. The feeding groove and fourth flagellum are positioned in the anterior region of the body and work together, involved in the function of endocytosis, enabling the movement of food particles towards the feeding groove. The flagella possess the 9+2 structure, common in flagellated eukaryotes. A single distinct nucleus is in the very anterior region of the body near the cytoplasm. Cysts Cysts are lemon or pear shaped, typically rounder and smaller than the trophozoite. One end of the cyst cell is rounded while the other end has a slight, blunt protuberance. The cyst wall is of even thickness except in the region of the protuberance where it is even thicker. Organelles found in the trophozoite, including the nucleus and cytostome, remain in the cyst stage and are usually viewable when stained under the microscope. While the vaned flagellum is present in the cyst stage, the three free anterior flagella are not, thus making the cyst non-motile. == References ==