Viruses may be small, but their influence is huge. These simple organisms are just a nucleic acid-coated in protein, but they can result in a wide variety of illnesses. Some can be deadly; others can be beneficial and an important part of your immune response.
For centuries doctors could see the results of viruses—illnesses such as polio, rabies, herpes, mono, and smallpox—but the particles working behind the scenes weren’t detected until the dawn of the 20th century. That’s when scientists discovered a bacteria-like being with a unique feature: It couldn’t reproduce without another being’s cells.
