Trichomonads

Trichomondads are characterised by protoplasmic plasticity so that various shapes may be assumed. However, they are usually pear-shaped and range in size from 4µm to 30µm. They posses three to five anterior flagella with a recurrent anterior fagellum which is attached to the body as an undulating membrane. They have been divided up by some authors on the number of anterior flagella: Ditrichomonas - 2 flagella;Tritrichomonas - 3 flagella;Trichomonas - 4 flagella; Pentatrichomonas - 5 flagella. However, some species, Tt. homonis for example, may have variable numbers of anterior flagellae. The flagella are connected to the kinetosomes of the blepharoplast complex and have the conventional 9 + 2 arrangement of fibres. They are also surrounded by a triple layered membrane which is continuous with the plasma membrane. The blephoroplast complex is a dark staining fibrillar complex situated at the anterior end of the cell consisting of several basal granules or kinetosomes which have direct connection with the flagella and other organelles. A parabasal body or Golgi apparatus is often seen.

Arising from the blepharoplast is a prominant tubular structure, the axostyle, which curves in a shell like manner around the nucleus and passes through the centre of the cell often emerging from the posterior end as a spike. In some species, the axostyle is a slender hyaline rod whereas in others it appears as a thick, conical structure with little or no posterior projection. A slender chromatic, basal rod, the costa, also arises from the blepharoplast and runs beneath the undulating membrane. In common with other members of the mastigophora Trichomonads have a single nucleus - usually spherical or ovoid and sometimes containing an endosome.

There is some debate regarding the presence of a cytostome in Trichomonads although claims have been made for one at the anterior end of the cell on the opposite side from the undulating membrane. It is more likely that particulate food is engulfed by pseudopodial projections which develop on the surface of the cell.

All trichomonads reproduce by simple longitudinal binary fission although sexual reproduction may also occur in some species especially those parasitic on invertebrates. In these species sexual reproduction is sometimes triggered by host molting hormones such as ecdysone.

Trichomonads Parasitic in Domestic Animals

Tritrichomonas foetus: This species has three anterior flagella and a trailing flagellum which is attached as an undulating membrane along the length of the body The axostyle is thick and hyaline and projects a short distance from the posterior end of the parasite. Transmission is almost exclusively sexual although there are rare reports of mechanical transmission. Several hundred parasites are required to initiate an infection which is confined to the reproductive tract and is probably life long in untreated animals. The severity of the disease varies from mild to severe and is often asymptomatic in the bull although an inflammed prepuce may occur.

Tritrichomonas gallinae:

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Trichomonads Parasitic in Humans

Pentatrichomonas hominis:This species is also refered to as Trichomonas hominis and has a variable number of anterior flagella (three to five) but typically five. The posteria flagella is attached by an undulating membrane which runs the full length of the cell. It has a relatively wide host range and is generally a harmless commensal found in the caecum and colon of man, other primates, dogs and cats. It is the least common of the 3 species inhabiting humans and is generally present in less than 2% of the population, although in many developing countries the prevalance is much higher (e.g. Mexico 32%). It is said to be less common in temperate climates but increased prevelance is usually directly associated with poor hygiene since the parasite is transmitted by the oral-faecal route via contaminated food, water and flies etc. Infections with T. hominis are easily distinguished from the other two species since there is a strict habitat restriction and this species will not survive in either the oral cavity or the genitourinary tract. Although not proved to be pathogenic infections are often associated with other protozoal gut parasites such as Entamoeba histolytica but their presence is probably coincidental and secondary to the primary pathogen.

Trichomonas tenax: This species has previously been refered to a T. buccallis

Trichomonas vaginalis:

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