PARASITIC PROTOZOA – 2012
November/December 2012 SSN-1059-6518 
Volume 25 Number 6
PARASITIC PROTOZOA
By Frank Hubbell, DO
What are protozoa, and why do we care?
Protozoa are single-celled organisms that can be symbiotic (live within another organism without causing harm) or parasitic (living within another organism at the expense of the organism, causing illness and death).
There are also many other single-celled microbiological organisms that cause disease and death. The science of biology sorts out all the various living organisms using taxonomy, the arrangement or defining of biological organisms by shared characteristics. In the world of microbiology, some of these unicellular organisms that can cause death and illness are viruses, bacteria, and protozoa.
VIRUS:
A virus is an infectious organism that consists solely of genetic material, DNA or RNA, surrounded by a protective shell, referred to as the capsid. They are obligate intracellular parasites, in that they cannot reproduce on their own. A virus has to inject its genetic material into another cell. Once inside the cell the viral genetic material will insert itself into the native DNA. It will then use that cell’s own DNA and turn it into a viral factory. Viruses are very tissue-specific, in that they will only invade a specific type of cell. For example HIV only invades and destroys a certain type of white blood cell, T-cells, and rabies only invades nerve cells.
BACTERIA vs. PROTOZOA:
Bacteria and protozoa are also unicellular organisms, but they are different from viruses because they can reproduce on their own, typically by binary fission. They also contain various organelles, eat, and excrete. Although in various shapes and sizes, bacteria and protozoa are very similar, except that bacteria are prokaryotes (They do not have a nucleus that contains their genetic material; the DNA is within the cell but, not in a separate membrane structure). Protozoa, on the other hand, are eukaryotes (They do have a nucleus with a cell membrane that contains their genetic material). Protozoa are also mobile in that they can have move by cilia, flagella, or by cytoplastic flow which provides them with the ability to swim through their environment.
