Virus

tiny invaders · biology · disease · microscopic

Smaller than bacteria. Viruses are so incredibly tiny that you need a special electron microscope to see them. They're actually smaller than the bacteria that viruses can infect.

Copy machines for cells. Viruses can't survive or make copies of themselves on their own. They have to break into a living cell and use the cell's own machinery to reproduce.

Everywhere on Earth. Viruses infect every single living thing, from animals and plants to bacteria and even the tiniest microorganisms. They're the most common biological entities on the planet.

First one discovered. Scientists first discovered the tobacco mosaic virus in the 1890s by noticing it made tobacco plant leaves get spotted and sick. This discovery started the whole science of studying viruses.

Millions exist. Scientists have carefully described more than 16,000 different virus species so far, but scientists think there are millions of viruses yet to be discovered.