I did find another article online however, that does give more information about this particular parasite in a human context. Apparently it does create minor character changes in humans, but nothing fatal to the average person. According to the article from Discover, research suggests the following character changes in people infected by T. gondii.
Carriers tend to show long-term personality changes that are small but statistically significant. Women tend to be more intelligent, affectionate, social and more likely to stick to rules. Men on the other hand tend to be less intelligent, but are more loyal, frugal and mild-tempered. The one trait that carriers of both genders share is a higher level of neuroticism – they are more prone to guilt, self-doubt and insecurity.
A second article, also from Discover (although two years older than the previous article), quotes a different research says the following effect T. gondii has on humans.
Those infected, he found, show a small, but statistically significant, tendency to be more self-reproaching and insecure. Paradoxically, infected women, on average, tend to be more outgoing and warmhearted than controls, while infected men tend to be more jealous and suspicious.
It might seem that such character traits are very minuscule and not worth alot of research time and effort but the first article goes on to say that in certain parts of the world, there is a huge portion of the population infected (67% in Brazil). This would raise a very important question on the meaning of how we look at cultures and people's characters. T. gondii has a prefered climate where it does spread in vast numbers. A small character change to the human population in such a region would certainly have an effect on national character traits and the historic cultural evolution of the region.
Nonetheless, the results are striking and one implicaiton is that climate could have a larger effect on culture than previously thought. Toxoplasma gondii‘s eggs live longer in humid, low regions so variations in climate could influence the global distribution of cultural traits. Perhaps, this could explain why men and women perform more distinct roles in society in countries in warmer climates. Other factors can also affect the risk of infection, including cat ownership and national cuisines that include undercooked meat.
We like to think of culture as something governed by the collective actions of free-thinking and free-acting humans. But Lafferty’s analysis shows us that if environmental factors like parasites can affect our thoughts and actions, no matter how subtly, they can have a strong effect on national cultures. In many cases, these effects could be much stronger than the agents that we normally believe to drive cultural trends. After all, more people around the world are infected with Toxoplasma than are connected to the internet.
On a further note in relation to human judgment (but not so much the involvement of external parasites), this old story seems very relevant. A sex offender in 2002 turned out to have a brain tumor that has been responsible for his perverted habits. Apparently after the tumor was removed he returned to his usual self until around a year later when the tumor returned and he restarted his habit of collecting pornography and harassing women!
Really, what all this tells us is that the brain is such a complex organ and it should never be very easy for us to make hasty judgments on anyone - even though I'm very guilty of it myself.