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There seems to be quite a few examples of parasites taking over the behavior of insects in a way that leads to the death of the host. A couple of examples include:

  • Spinochordodes tellinii: A nematomorph hairworm that causes crickets and grasshoppers to jump into water, and likely drown, as part of their life cycle.
  • Ophiocordyceps unilateralis: A fungus that causes ants to leave their desired habitat for the habitat required for the fungus to reproduce while consuming the ants internal organs.

In mammals, a common example is:

  • Toxoplasma gondii: A single celled parasite that appears to make rats attracted to cat pee in an attempt to continue its life cycle within the cat. Additionally, humans can be infected with Toxoplasma gondii via contaminated meat, vegetables, and cat feces. In fact, there is a study of Danish medical records from 45,788 women in which the rate of self harm increased 50% for women suffering from chronic toxoplasmosis and the rate of attempted suicide was 80% higher. However, direct correlation between the increases could not be linked to the these higher rates due to the possibility of other factors such as depression.

So it seems that there is some widespread evidence of parasites causing a host to act in a potentially lethal way, but the evidence that I could find for humans seems to be minimal and yet to be proven. Are there any examples of parasites causing humans to act in a risky, potentially deadly, manner?

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There is a link established between Candida and Aspergillus fungal infections and mental illness of schizophrenia and depresssion. Over prescriptions of antibiotics and use of antibiotics in cattle ranching, subject people to excessive antibiotics. This causes a die off of natural gut flora and consequent fungal overgrowth. Fungal metabolites (aflatoxins) have been linked to anorexia,depression and schizophrenia. Pubchem lists lists behavioral acute anorexia for aflatoxin G1. Research published in Journal of Antimicrobial Therapy, suggest that some SSRI antidepressants have an antifungal effect. Ethyl alcohol (alcoholic beverage) is a fungal metabollite of brewers yeast that is well known to impair human behaviour in a negative way. I have been unable to find any research into using antifungal agents to treat mental illness.

A fungus that thrives in soil, contaminates grain, is distilled into a beverage that causes drunk driving and death, and returns the host to the soil has also completed its life cycle. Similar to the ant example in your question.

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