What does an memetic infection look like? Well, you would encounter something (probably on the internet) that seems very compelling. You think intensely about it for a while, and it spurs you to do something - probably to post something related on the internet. After a while, the meme may not seem that compelling to you anymore, and you wonder why you invested that time and energy. The meme has reproduced itself. For example, Bruce Sterling's response to the 'New Aesthetic' is a paradigmatic example of memetic infection: he encountered it, he found it compelling, he wrote about it, I read about it and now I know about it. (Note that the word 'infection' has a stigma to it, but I don't mean it to be necessarily a bad thing. I will use 'disease' to mean 'infection with bad consequences'.)

Now, let me jump to an apparently unrelated concept - Viral Eukaryogenesis. If I understand correctly, Viral Eukaryogenesis is the theory that eukaryotes (including you and me) are inheritors of a bargain between two kinds of life - metabolic life and viral life, something like the way lichens are a bargain between fungi and algae. The nucleus that characterizes eukaryotes is supposed to be descended from a virus protein shell, and the membrane-fusion proteins that we use for gamete fusion (crucial for sex) are supposed to be descended from viral infection proteins. I am not a biologist, but my understanding of the state of biology is that it is an interesting hypothesis, as yet neither proven nor disproven. However, I'm going to talk as if it were true, because I'm actually trying to make an analogy with memes.