Principles of Epidemiology and Microbiology
Lesson 2: Public Health Microbiology
Section III: Viruses
2-12
Section III. VIRUSES
2-12. GENERAL
Viruses are submicroscopic, obligate, filterable intracellular parasites. In other words, they are organisms that are too small to be seen with an ordinary light microscope and which are totally dependent upon a host cell for survival. They range in size from about 15 mµ to 300 mµ in diameter. Viruses are true parasites, in that they have no means of metabolism of their own. They cannot be grown on artificial media, as they need living cells to exist. They are considered by some authorities as falling within the gray area between the lowest forms of life and complex organic chemical molecules.
