By: Carolina Gonzalez

What is a Virus?

A virus is a tiny organism that can only replicate inside the cell of a host organism. Because of this they can be considered either living or non-living. They replicate by finding a host and inserting their genetic material into it, taking over the cells functions. The cell still reproduces but with more infected cells. Viruses can infect all organisms from plants and animals to microorganisms including bacteria. Viruses can lead to illnesses that range from the common cold to rabies. Today, virologists know of approximently 5000 different viruses that can be described in detail.

Characteristics Of Viruses

  • Can be considered living or non-living
  • Are unicellular
  • They do not metabolize because they do not have ribosomes or enzymes
  • They do not grow but they can reproduce
  • They have a nucleic acid core that contains DNA or RNA

Sturcture of a Virus

Virus structures vary depending on the host but they general have the same general structure.

  • The head region contains genetic material

  • The Capsid is made of proteins and glycoproteins

  • There is a membranous envelope surrounding the Capsid

  • The tail region is a protein structure that helps in binding to the surface of the host cell

  • They have spikes that help attach to the host cell

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Helpful Vs. Harmful

For the most part viruses are harmful. They can cause disease in humans, animals, and plants. These diseases include the common cold, Rabies and Tobacco Mosaic in plants.

Even thought viruses are harmful they can be turned into vaccinations that we can use to protect us from those viruses. We first started getting vaccinations for Cowpox and it is the reason that we continue to get them.

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Yellow Fever

Yellow Fever, which was know as "American Plague" at the time, first occurred in the late 1690's. About 100 years in the summer of 1793 refugees from a yellow fever epidemic in the Caribbean fled to Philadelphia. Within weeks of them arriving people started having symptoms. By October there where approximately 100 people dying a day. During this the local city government collapsed and federal authority's evacuated the city to face the epidemic. Eventually a cold front came wiping out most of the mosquitos which are the cause of Yellow Fever. By the end more then 5,000 people had died. 20,000 people still die every year from this disease.

Yellow Fever is cause by mosquitoes, similar to Malaria. Yellow Fever begins with a fever and muscle pains. Then your liver and Kidney slowly stop working. People often become delirious before dying.


Because viruses live inside cells they are harder to treat. Antibiotics do not work because they move through the bloodstream and viruses are in the cells.
Flu Attack! How A Virus Invades Your Body


True or False

  1. A Virus can only replicate outside of the cell of the host organism. _____________

  2. Viruses can be considered living or non-living. _____________

  3. Yellow Fever was also know as the "European Plague". _______________

  4. Viruses can not cause diseases in Plants._______________

  5. Viruses have spikes used to attach to the host cell. ______________