Abstract: Parasites, considered here in the general sense to include anything that lives and multiplies in another host organism, are as old as life itself. Yet, at the same time, new parasites are constantly emerging and adapting to their hosts anew. What outcomes can we expect for this process?The conventional wisdom in many medical textbooks is that well-adapted parasites are harmless to their hosts. The argument is that it is disadvantageous for the parasite to kill the host it relies on for reproduction. Empirical observations, however, paint a more complex picture. Why is it that some parasites cause high levels of host damage (i.e. virulence), whereas others are relatively benign?After briefly reviewing empirical examples, I introduce Anderson and May's classic theory of the evolution of virulence following [Nowak 2006]. Then, deriving the basic reproductive ratio I discuss the evolution of virulence under different conditions. Finally, after exploring the effects of introducing superinfection, I end with recent results on the impact of imperfect vaccines on the evolution of virulence.

us02web.zoom.us/j/4082603129