This excerpt from a textbook discusses the various mechanisms that pathogens use to cause disease. It explores the concept of virulence factors, which are molecules produced by pathogens that enable them to adhere to host cells, invade tissues, evade the immune system, and cause damage. The text focuses on bacteria, viruses, fungi, and parasites, highlighting specific examples of virulence factors and their effects on the host. It provides detailed descriptions of toxins, exoenzymes, capsules, antigenic variation, and other strategies employed by pathogens to overcome host defenses.