Microorganisms, microbes and "beasties"
Introduction to microbes (extract from "And You Thought You Were Safe")
As a matter of fact, viruses are about the smallest of the microorganisms. And because a virus is so small, it can gain entry into our cells and even into bacteria. A virus cannot replicate by itself. It needs a host cell, which is forced to function as a 'factory' to produce viral copies. During the process of reproduction, many copies of a single virus type are replicated in a host cell. Once the host cell produces enough copies, it may burst only to release the newly made viruses to infect adjacent cells. From subsequent rupture and release of the newly formed viruses, the host cell dies. Alternatively, the host cell may not die. Some host cells simply keep manufacturing and "shedding" viral particles into the extracellular environment. The newly released viral particles then have the opportunity to infect adjacent cells of the particular tissue. During this process many cells may become infected from the replicated viruses and the cycle repeats itself continually until the infection is resolved by the immune system. Although, viral resolution is common, it is not guaranteed. Many viruses have the ability to establish permanent residency. These infections become latent and may later undergo periods of reactivation and remission, causing different degrees of illness throughout the lifetime of the infected individual.
There is only one group of infection causing entities smaller in size than viruses. These are called prions and are discussed in the following chapters. Prions are protein-containing particles, and are what we believe to be the etiological agent causing the neurodegenerative diseases BSE, CJD and others.
Microorganisms such as bacteria, fungi, and protozoa, can cause tissue damage through direct invasion of human tissues, liberation of toxins and enzymes, and by causing host mediated responses such as inflammation. As we shall see, some microorganisms can also find their way into individual cells, similar in mechanism to the virus.
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