Viruses are the most abundant pathogen on Earth. Viruses are microscopic parasites, generally much smaller than bacteria. They lack the capacity to thrive and reproduce outside of a host body such as bacteria, animals, or plants. Each viral particle, or virion, consists of a single nucleic acid - RNA or DNA - surrounded by a protein coat. The shapes of these virus particles range from simple helical and icosahedral forms to more complex structures.
