Host–virus interactions: battles between viruses and the hosts (and nonhosts)

Coevolution and adaptation between viruses and their hosts are often portrayed as a biological arms race. Viruses are equipped with an array of mechanisms to counteract host defenses that are poised to recognize nonself and activate antiviral pathways, which in turn have driven the development of mechanisms that restrict infection in host organisms across all domains of life. Invariably, the opposing goals of the host organism and the virus have led to the dramatic diversification of viruses and host defense responses, as well as a full spectrum of different outcomes—from mutualism to parasitism, and everything in between in a wide range of symbiotic interactions. In this chapter, we examine various mechanisms developed by each side to ensure survival and briefly review the effects of viral infections on the fitness of the host, that is, its overall metabolism and performance.