On Andrew Sullivan’s blog there’s been a thread on this question. I’ll track back and read it from the beginning, but the question is interesting. In the Death and Immortality course we’ve touched on suicide here and there, mostly when considering whether death is a harm.
Warning! The discussion is on the creepy side. Below is a comment from a reader.
There is good evidence that Toxoplasma gondii — the parasite often found in cat feces that poses a risk to human fetuses — spreads by affecting the behavior of its rodent hosts. Infected rodents show decreased fear-responses to cats, which is thought to increase the likelihood that the cats will then eat the rodents, allowing the protozoa to complete the next phase of their reproductive cycle in a feline host.
Your reader wrote, “Can you image something like that in humans? Scary.” There is a growing body of evidence, which is somewhat controversial, that toxoplasmosis may induce behavioral alterations in infected humans as well.