Millions of Americans alone, not to mention many more people worldwide, might be infected with a parasitic single celled protozoan called Toxoplasma gondii.
Most people will be asymptomatic, though some people might experience fascinating behavior and personality modification, generally in ways detrimental to our survival. An untold number of vehicular accidents might be due, in part, to T Gondii, to give an example.
It’s been known for some time that there are parasites that modify the behavior of insects. The possibility that T Gondii might cause subtle changes in the personality of a human host is an intriguing concept. The article suggests that even healthy and basically symptom-less people might be adversely affected. For example:
Those who tested positive for the parasite, both studies showed, were about two and a half times as likely to be in a traffic accident as their uninfected peers.
More intriguing, the parasite affects men and women differently; it affects emotions such as fear and anxiety; it affects personality traits such as introversion/extraversion; it even alters how we perceive the smell of cat urine.
Other parasites cause similar and equally fascinating behavior change, at least in some species:
Consider Polysphincta gutfreundi, a parasitic wasp that grabs hold of an orb spider and attaches a tiny egg to its belly. A wormlike larva emerges from the egg, and then releases chemicals that prompt the spider to abandon weaving its familiar spiral web and instead spin its silk thread into a special pattern that will hold the cocoon in which the larva matures. The “possessed” spider even crochets a specific geometric design in the net, camouflaging the cocoon from the wasp’s predators.