Toxoplasma Gondii is a parasite that has infected between 20% and 80% of humans depending on the country (around 60 million in the US). Infection typically occurs through contact with cats or eating undercooked meat, with the emphasis on cats being due to the parasite only being able to reproduce in the feline gut. T. gondii can also be transmitted by an infected pregnant host onto her offspring, or by blood transfusion (note this also means sexual transmission is possible through an infected male host if the receiver is cut, or through the anal wall).
It has been demonstrated that T. gondii manipulates infected rats into 'seeking out' cats, which in turn causes the parasite to infect the cat once the rat is eaten. The method it achieves this is by making the rat sexually attracted to the scent of cat urine. As this scientific journal suggests, since the parasite does not know whether it is in a rat or not (and all non-feline hosts are "dead-ends") it is likely that the parasite reacts in the same manner to being in a non-feline host, regardless of what type of host it is.
Why should you care?
The above journal describes the personality differences between T. gondii infected people and non-infected people, according to the Cattell model. For infected men, they scored significantly higher on traits vigilance and apprehension and lower on rule consciousness, perfectionism and on an additional variable "Relationships" (analagous to warmth on Cattell), whereas for infected women, they scored higher on warmth, apprehension, rule consciousness and "Relationships" (see previous link for meanings of terms). The journal also notes the association between T. gondii infection and schizophrenia, lower coordination skill (2.65 times higher risk of traffic accidents) and loss of concentration. Note for the "infected" individuals the infection was latent, meaning the effects are permanent since infection cannot be undone (as far as I can tell).
It is suggested that the parasite has these influences through various means, including brain inflammations and cysts, regulating dopamine levels and increased testosterone. The increased testosterone also accounts for the increased sex ratio (more male births), increased height in men and longer pregnancies. It is also thought that this may be advantageous for the parasite in order for the host's immune system to be weakened to increase its chance of surviving in the host.
Also according to Anon (scroll down to the first post with sources listed underneath), in human hosts the parasite makes them more sexually attracted to men. The possibility of sexual transmission, combined with this would mean homosexuality is (at least partially) a result of infectious disease. This makes all those stories of gay individuals who had their first 'sexual experience' at a young age a lot more sinister (think Milo and George Takei).
To recap: many cats are infected with T. gondii and infect their owners. T. gondii changes the personality of their hosts permanently to make them more suspicious, oppositional, guilt-prone, insecure and have lower coordination and concentration. In men it also makes them more self-indulgent, undisciplined and worse at relationships (yet taller). For women however, it makes them more warm, dutiful, moralistic, but more likely to have male children who are infected. It may also be a cause of homosexuality in men.
tl;dr - don't get a cat
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[–] SocialJusticePanda ago
Or you could just not spoon your cat.