The ciliates belong to the family Ciliophora.  They possess simple cilia or compound ciliary organelles,2 types of nuclei and a large contractile vacuole.  The only member of the ciliate family to cause human disease is Balantidium coli.

Balantidium coli

Introduction.

Balantidium coli is widely distributed in warmer climates which is where human infections most commonly occur.  The organisms inhabit the large intestine, caecum and terminal ileum where they feed on bacteria.

Morphology

The cyst is spherical or ellipsoid and measures from 50 - 70m.  It contains 1 macro and 1 micronucleus.  The cilia are present in young cysts and may be seen slowly rotating, but after prolonged encystment, the cilia disappear. 

Trophozoites of B. coli measures approximately 50-100m in length but have been known to attain lengths of up to 200m.  It is oval in shape and covered in short cilia.  A funnel shaped cytosome can be seen near the anterior end.  In an unstained preparation, the organisms are easily recognised because of their size and rapid revolving rotation.  In a stained preparation, the characteristic macro and micronuclei may be observed. 

Clinical Disease

Severe B. coli infections may resemble amoebiasis.  Symptoms include diarrhoea, nausea, vomiting and anorexia.  The diarrhoea may persist for long periods of time resulting in acute fluid loss.  B. coli also has the potential to penetrate the mucosa resulting in ulceration.  Extra-intestinal disease has also been reported but rarely.

Laboratory Diagnosis

Wet preparations of fresh and concentrated stool preparations reveal the characteristic cysts and trophozoites.  They are easier to identify in wet preparations than permanently stained faecal smears.