Epistatic

Hi! I'm a Graduate student specificially studying Toxoplasma's behavioral modification abilities in mice! I think I'm qualified to answer this.

The data is very, very solid on Toxo's manipulation of rodents to become attracted to cats. This has been well-replicated, although a mechanism is still elusive.

In humans, research has linked Toxoplasma infection to a lot of things. The results of decreased reaction time and personality changes mostly come out of a lab in the Czech Republic, conducted via the "gather a hundred undergrads and make them do things" method, or by screening of army recruits. I'm not very confident in those results, because the experimenters screened for a LOT of things, and the significance of the differences seen was not great. This is the same author who at one point used the phrase "results in X approached significance" in an abstract of his paper.

Toxoplasma has been linked in a number of studies to schizophrenia: many authors describe that schizophrenics are 2 to 3fold more likely to be harboring Toxoplasma than the general population. Whether this is correlative or causative is unclear, however. It could be that lower hygiene and ability to self-care in people afflicted by schizophrenia, as well as elevated risk behavior, could lead to the higher infection rates seen.

If Toxoplasma did have a causative relationship with schizophrenia, you would expect rates of schizophrenia to correlate with rates of Toxoplasma infection from country to country. However, seropositivity of Toxoplasma varies from 10-30% in North America/ Europe, to as high as 80% in Central America. However, incidence of schizophrenia is completely flat worldwide.

The primary hypothesis of Toxoplasma's behavioral manipulation is that the parasite uses parasite-encoded tyrosine hydroxylases, the rate-limiting step in dopamine synthesis in neurons, to modulate neurotransmitter firing in rodents.

However, it was recently (within the last few months) demonstrated that rodents infected with a defective Toxoplasma strain that is incapable of remaining encysted in the host, still causes rodents to demonstrate cat-attraction behavior, many months after no trace of parasite remains in the rat. Which suggests remodelling of the rodent brain at some point during active infection instead.

That's as far as science knows, for now. Once I finish my thesis I'll toss you guys an update!

Sorry to hijack your AMA, but I can't help but love what I do and talking about it.

I've been filling them in as I see them! There are a lot though, and quite a few repeats. Thanks! Science-five!

One third of people around the world have Toxoplasma in their brain. Think of your two best friends. If one of them is crazy, you're probably fine!

Other parasites that affect host behavior include:

the horsehair worm, which drives insects to drown themselves in bodies of water, delivering the worm back to its breeding ground.

the trematode Euhaplorchis californiensis, whose life cycle goes from shorebirds to snails to krillifish and back into shorebirds. Infected krillifish become more likely to swim close to the surface of the water, jerk around, and swim sideways, exposing their sides to catch the sun, attracting the birds that eat them.

the Emerald Cockroach wasp Ampulex compressa, which uses its stinger to specifically destroy the structure in a cockroach's brain that controls its escape reflex, resulting in a zombified cockroach incapable of reacting to dangerous threat, which gets helplessly led, like sheep to the slaughter, into the wasp's nest to serve as fresh, live food for the wasp's larvae.

http://newyork.cbslocal.com/2014/02/06/report-officials-distribute-100000-condoms-in-olympic-villages/

The Olympic Village in 2012 gave out 100, 000 condoms. And this supply, among other things, was quickly exhausted.