Trichomonas hominis

Introduction

This flagellate is of cosmopolitan distribution.  It is thought to be non-pathogenic although it has been associated with diarrhoeic stools.  It is the most commonly found flagellate next to Giardia lamblia and Dientamoeba fragilis.

Morphology.

T. hominis has no cystic stage.  The trophozoite measures from 5-15m in length by 7-10m in width.  The shape is pyriform and has an axostyle which runs from the nucleus down the centre of the body and extends from the end  of the body  and undulating membrane which extends the entire length of the body and projects from the body like a free flagellum. It has 4 free flagella and a single nucleus at the anterior end.

A stained preparation of Trichomonas hominis

Laboratory Diagnosis

In a fresh stool, the flagellates move very rapidly in a jerky, non-directional manner.  The axostyle and undulating membrane are diagnostic.  .

Chilomastix mesnili

Chilomastix mesnili is of cosmopolitan distribution although found more frequently in warm   climates.  It is thought to be non-pathogenic although the trophozoite has been associated with diarrhoeic stool.

Morphology

The cyst is 6-9m It has a large single nucleus with a large karyosome.  It has a prominent side knob which gives it a characteristic lemon shape.   The cytosome is evident with a curved shepherds crook fibril.

The trophozoites of C. mesnili are pear shaped and measure 10-20m in length.  It has 1 large nucleus with a small karyosome and 3 flagella which extend from the nucleus at the anterior end of the parasite.  A distinct oral groove or cytosome can be seen near the nucleus.  It moves in a directional manner.

Laboratory diagnosis

The characteristic lemon shaped cysts can be seen in a formol-ether concentrate.  Motile organisms can be seen in a wet preparation of a fresh stool however the characteristic morphology is evident in a permanently stained preparation.

Enteromonas hominis

Introduction

Enteromonas hominis is a small flagellate and is rarely encountered.  It is found in both warm and temperate climates and is considered to be non-pathogenic.

Morphology

The cyst is oval and is 6-8m in length.  It has up to 4 nuclei with a bipolar tendency.

The trophozoite is oval and 4-10m in length.  It has a jerky rotation.  It has 4 flagella, 3 anterior flagella and one adheres to the body ending in a tail.  It has one nucleus with a large karyosome which is evident in a stained preparation.

Laboratory Diagnosis

The cysts are seen in a formol-ether concentrate.  The cysts have no distinguishing characteristics and thus can be confused with E. nana or even yeasts.  The characteristic trophozoites can be seen in a permanently stained faecal smear.

Retortamonas intestinalis

Introduction

Retortamonas intestinalis like Enteromonas hominis is a small flagellate  found in both warm and temperate climates and is considered to be non-pathogenic.

Morphology

The cyst is small and pear shaped.  It is 4-7m with 1 large nucleus frequently near the centre.  Th fibril arrangement from the nucleus is suggestive of a birds beak.  This is characteristic.

The trophozoite is small, measuring between 4 and 9m.  Its movement is jerky and rotational and has 2 anterior flagella and a prominent cytosome which can be seen in an unstained preparation.  It has a relatively large nucleus at the anterior end with a small compact karyosome.

Laboratory Diagnosis

The small pears shaped cysts are uncharacteristic in an unstained formol-ether preparation.  However, the addition of iodine reveals the characteristic bird beak fibrillar arrangement in the pear shaped cyst.

In a fresh stool preparation, the 2 anterior flagella and cytosome can be seen in the trophozoite.  In a permanently stained preparation, the large nucleus with small central karyosome is diagnostic