A common parasite hosted by mammals that reproduces specifically in felines,
Toxoplasma gondii, has been shown through tests to primarily congregate in the amygdala(center of brain controlling fear responses, among other things) in mice. The parasite's mode of travel seems to involve hijacking mobile immune cells(dendritic cells), and inducing them to hyperactive movement by an unknown mechanism.
Normal mice would respond to the smell of cat urine with fear. However, infected mice are known to lose this response, and instead be somewhat attracted to the smell. All other tested fear responses were still intact, showing that the parasite works with great precision. This leads mice to put themselves in positions where they would be eaten by cats. And eventually the parasites find way to their breeding ground, the feline intestine.
As a relevant side-note,
Toxoplasma gondii infects humans, usually through exposure to infected cat feces. While normally harmless, if the host's immune system is compromised, it can lead to brain-damage and schizophrenia-like symptoms, giving depth to the phrase, "crazy cat-lady"...
Short, NewScientist article:
http://www.newscientist.com/article....ine-news_rss20
Extended, NY Times article with introduction to
Toxoplasma gondii:
http://www.nytimes.com/2006/06/20/sc...pagewanted=all
