Protozoa are single celled eukaryotic organisms within the animal kingdom, rather than prokaryotes like bacteria.


Protozoa are motile and are found in a variety of aqueous environments, soil and as human parasites.

They can feed on other microscopic organisms including bacteria, algae and fungi.  Protozoa have a complex life cycle, involving both active, replicating stages and dormant cystic stage.  The cyst formation is an adaption to enable the protozoa to survive under harsh environmental conditions.

Infections Caused by Protozoa

They are found in the oral cavity in the pockets of people with periodontally active disease.

Protozoa are not primarily the cause of any specific oral infections. However, protozoa do cause a number of major infectious diseases such as gastrointestinal infections like giardiasis, cryptosporidiosis and malaria one of the commonest infectious disease in the world affecting approximately 219 million people.

Protozoa and Dental Unit Waterlines (DUWL)

Their main impact on dentistry lies with dental unit waterlines.

Free living amoebae found in tap water and in the sludge deposits that can forms at the bottom of water tanks feed on legionellae bacteria. The legionellae are not killed by the amoeba, but can survive, grow and multiply unharmed within protective vacuoles.

Free-living amoebae like other protozoa, are well adapted to their hostile environmental conditions and are resistant to desiccation, elevated temperatures and various disinfectants.

The amoebae provide the legionellae both protection against adverse environmental conditions and transportation. The amoebae are important vectors in the transmission of legionella and the development of pneumonia in infected individuals.

Legionellae by living intracellularly are not only protected from the killing action of disinfectants, but also from cells of the immune system which would otherwise in engulf and destroy the bacterium.