Every so often news about a viral outbreak goes viral and catches widespread public attention in the media. Human immunodeficiency virus (HIV), West Nile virus, avian influenza (bird flu), Ebola, Middle East respiratory virus, and Zika virus have each become, in a flurry of headlines and broadcasts and interviews, the focus of the media’s spotlight. And then, like other crises, they fade from view leaving the public with a new health concern to worry about but little knowledge of the actual factors involved in the problem. Behind the scenes, however, scientists are continually at work trying to understand and defend against these insidious infectious agents.

Viruses are perfect parasites. It has been known for decades that once a virus gets inside a cell, it hijacks the cellular processes to produce virally encoded protein that will replicate the virus’s genetic material. Viral mechanisms are capable of translocating proteins and genetic material from the cell and assembling them into new virus particles. Contemporary research has revealed specific mechanisms viruses use to get inside cells and infect them. An individual viral particle, called a virion, is a far simpler structure than a bacterium. It has often been questioned whether a virus is alive. It is certainly not living in the everyday sense of the word. Virions consist of genetic material—DNA or RNA enclosed in a protein coating. Many viruses, called enveloped viruses, have an additional outer membrane that encloses the protein coat. This membrane envelope is material co-opted from the cell’s own membrane. As the new virion buds out from an infected host cell, it is wrapped by the cell’s bilayer membrane and carries with it any protein that happens to be embedded in the membrane at the budding site. Enveloped viruses are then free to begin a new cycle of infection by fusing their cell-derived envelope with the cellular membrane of an uninfected cell.