Viral attack. Three-dimensional computer graphic representation of spiked viruses (at top) on the attack. The microscopic surface of a cell is depicted at bottom. Viruses are tiny infectious agents. They cause ailments ranging from warts, the common cold and influenza, to serious diseases like rabies, Lassa fever and AIDS. The rounded viruses (multicoloured) consist of a protein coat that houses genetic material. Spikes on the coat allow these viruses to bind to the surface of host cells before infection. Spiked viruses include HIV which causes AIDS, and the influenza virus. Viral spikes may change structure to form a new viral strain which can spread as an epidemic.