Spillover: Animal Infections and the Next Human Pandemic

by David Quammen

Across the outer surface of the envelope, the virion may be festooned with a large number of spiky molecular protuberances, like the detonator stubs on an old-fashioned naval mine. Those spikes serve a crucial function. They’re specific to each kind of virus, with a keylike structure that fits molecular locks on the outer surface of a target cell; they allow the virion to attach itself, docking like one spaceship to another, and they open the way in. The specificity of the spikes not only constrains which kinds of host a given virus can infect but also which sorts of cell—nerve cells, stomach cells, cells of the respiratory lining—the virus can most effectively penetrate, and therefore what sort of disease it may cause. Useful as they are to a virus, though, the spikes also represent points of vulnerability. They are the primary targets of immune response by an infected host. Antibodies, produced by white blood cells, are molecules that glom onto the spikes and prevent a virion from grabbing a cell.