Parasite that control the minds of their hosts:
Toxoplasma gondii is a parasite that normally infects cats and rats. Among other things, it seems to make rats less sensitive to the scent of cat urine, meaning that if they smell it, they don't immediately run away. This makes them easier targets for cats. The thing is, lots of people have cats. And this means that lots of people have also been infected by T gondii. From Wikipedia:
Looking at humans, studies using the Cattell’s 16 Personality Factor questionnaire found that infected men scored lower on Factor G (superego strength/rule consciousness) and higher on Factor L (vigilance) while the opposite pattern was observed for infected women. This means that men were more likely to disregard rule and were more expedient, suspicious and jealous. On the other hand, women were more warm hearted, outgoing, conscientious and moralistic. Mice infected with T. gondii have a worse motor performance than non-infected mice. Thus, a computerized simple reaction test was given to both infected and non-infected adults. It was found that the infected adults performed much more poorly and lost their concentration more quickly than the control group. But, the effect of the infection only explains less than 10% of the variability in performance (i.e., there could be other confounding factors). Correlation has also been observed between seroprevalence of T. gondii in humans and increased risk of traffic accidents. Infected subjects have a 2.65 times higher risk of getting into a traffic accident. A similar study done in Turkey showed that there is a higher incidence of Toxoplasma gondii antibodies among drivers who have been involved in traffic accidents. Furthermore, this parasite has been associated with many neurological disorders such as schizophrenia. In a meta-analysis of 23 studies that met inclusion criteria, the seroprevalence of antibodies to T. gondii in people with schizophrenia is significantly higher than in control populations (OR=2.73, P<0 .000001="" a="" href="https://en.wikipedia.org/wiki/Toxoplasma_gondii#cite_note-TorreyMeta-80">0>More recent studies found that suicide attempters has significantly higher IgG antibody levels to T. gondii than patients without a suicide attempt. Infection was also shown to be associated with suicide in women over the age of 60. (P<0 .005="" a="" href="https://en.wikipedia.org/wiki/Toxoplasma_gondii#cite_note-Ling2011-82">0>So crazy cat ladies? The behaviors may be caused by parasites.
There are a lot of tabloid-esce posts on the subject of parasites that affect human behavior. Here is a relatively measured post from Discovery Magazine that looks at a few parasites, including rabies.
Wikipedia has a good introduction to a wide range of parasites that affect the behavior of their normal hosts. One they describe is the horse hair worm that, after eating the insides of their insect prey, cause it to leap into water and drown. I have personally seen such parasites in South Korea and in Canada. Both photos below were taken in Korea:
I sure made the ten-year-old boys who carried this worm in their bare hands wash their hands repeatedly and thoroughly!
One science-based comic I read often offered this comparison of how a parasitic fungus of ants might similarly affect humans:
Follow the link to see the end -not really punchline - of this comic. Click on the red dot below the comic for an extra panel.
This is probably my most horrific post based on Hallowe'en. Lighter fare coming!