Infection vs. Disease
You may have heard the terms “infection" and “disease" in health class. While they may sound like the same thing, they differ on how the virus has affected the person’s body. An infection refers to viruses entering the body and replicating. When it is considered a disease, the viruses have destroyed some healthy cells in the body, and the symptoms of the illness begin. That is when you will see a person coughing, hopefully covering her mouth so that the virus does not spread to you. So how do viruses work in the body?
The life cycle of a virus once it has entered the body can be broken up into six steps. First is attachment in which the virus binds to the surface of the host cell. The virus has receptors and it can attach itself to the host cell if it can connect to the complementary receptors found on the cell membrane. Once the virus attaches itself to the cell membrane, it needs to get into the cycle to reproduce. That step is called penetration. The method of entry depends on the type of virus. For example, with a bacteriophage, the protective protein coat stays on the outside and the nuclei acid goes into the host cell. Some viruses may enter through a process called endocytosis, as shown by this diagram from Brooklyn College.
The next stage in a working virus is uncoating, in which the infectious nuclei acid gets released from its protective coat. With bacteriophages, penetration and uncoating happen at the same time. For other viruses, enzymes can break it down. Now that the infectious material from the virus is in the host cell, it starts replicating itself. This stage, synthesis, can be divided further into three parts: transcription, translation and genome replication. In transcription, a complementary strand of RNA is made for the virus’ DNA. During translation, that complementary RNA is turned into proteins by the host’s ribosomes, with the full copy of the virus’ genetic material completed in genome replication. Once all the parts are made, full viruses, like the one that infected the host cell, are created in assembly. After these replicated viruses are completed, they go through the last stage — release — in which they can go on to infect other healthy cells. The host cells in which the virus reproduces eventually get destroyed.