VIRUSES

Found in all living things, from bacteria and fungi to plants and animals, viruses are by far the smallest microbes. They can appear as spirals, 20-sided figures, or assume more complex forms.

Viruses consist mainly of genetic material—DNA or RNA—which may occur in a single or double strand, depending on the species. They are not cells, however, and cannot carry out life functions on their own. They live in the cells of other species, using the host cells to grow and produce new viral particles. As they take over genetic material in order to reproduce, the host cells often die.

There are many viruses that are dangerous to humans. However, a virus that attacks non-human cells, such as bacterium in animals or plants, poses no threat to our health.

A Common Cold Virus

Adenoviruses affect most children around the world by the age of six. They can cause the common cold, as well as other respiratory illnesses, pink eye, and diarrhea. Differences in the proteins that surround the viruses' genetic material determine which disease the virus causes.