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Summary
Benjamin Franklin should have included infectious disease as a third certainty of life alongside death and taxes. We will always be plagued by pests and pathogens because they generally have shorter life cycles than their hosts, allowing them to evolve rapidly to avoid host defenses. The use of antibiotics, for example, may select for drug-resistant strains of bacteria and, in agriculture, the widespread cultivation of a disease-resistant crop is often followed by the appearance of resistance-breaking strains of the pathogen. Whenever a host acquires a novel defense, the pest will, eventually, evolve a corresponding counter-defense system. On page 118 of this issue, Weiberg et al. (1) describe a strategy in which a fungal parasite uses RNA to block a host's defense system