How Long Has This Been Studied
This kind of study has only been started very recently to try and find a connection to parasites that attack insects and animals, and how they effect humans.
How This Effects People and Society
These parasite can have an effect on how people and animals behave, which, if it isn't known the parasite was inside a person, it could lead to people panicking, especially if the person was violent.
How Its Related To Chemistry
In most cases, the infecting parasite can change the behavior of its host by controlling their dopamine levels. Dopamine, the chemical in the brain which controls pleasure, at low levels can cause a person to become depressed, sad, or even violent. While at high levels it causes happiness.
The study of these parasites has been primarily focused on how they effect insect and animals, because the only way to see their full effect on humans would be to infect a group of people, which would never be aloud.
The Future of Neuroparasitology
It is estimated that millions of people in just the U.S. are infected with one or more parasitic organisms and those numbers are though to only increase in the future. But with the number of very few number of people trying to study these parasites and their effects, the number of infections and diseases are only going to increase.
Neuroparasitology is science fiction, the things some parasites are able to do seems something out of a movie, and that's what's scary. We don't want to watch The Thing and think that it could happen. But the fact is that there are creature that can fully control their hosts, and that's almost all we know.