[Behavioural Changes Caused by Parasites: The Parasite Manipulation Hypothesis].

Area of Science:

• Microbiology
• Parasitology
• Neuroscience

Background:

• The human microbiome includes bacteria, archaea, fungi, and viruses, crucial for ecosystem symbiosis.
• Parasites, comprising 40% of Earth's biodiversity, rely on hosts for their life cycle completion.
• The parasitic manipulation hypothesis suggests parasites alter host behavior, observed primarily in invertebrates.

Purpose of the Study:

• To explore mechanisms by which parasites utilize hosts and involved signaling pathways.
• To critically evaluate the evidence for adaptive parasitic manipulation in humans, using toxoplasmosis and malaria as examples.
• To discuss alternative explanations for observed host behavior changes during parasitic infections.

Main Methods:

• Review of existing literature on parasite-host interactions and signaling pathways.
• Analysis of the parasitic manipulation hypothesis, focusing on the requirements for proving adaptive manipulation.
• Examination of alternative explanations, such as host inflammatory and immunological responses.

Main Results:

• The adaptive manipulation of humans by Toxoplasma gondii lacks definitive proof of a cause-effect relationship.
• Inflammatory and immunological host processes offer alternative explanations for altered neuronal signaling during infection.
• Observed associations between parasitic infections and host behavior warrant further investigation.

Conclusions:

• While direct evidence for human parasitic manipulation is lacking, the phenomenon is well-documented in invertebrates.
• Host-side immune responses may underlie observed behavioral changes, rather than direct parasite-driven manipulation.
• Investigating these associations could lead to novel diagnostic and therapeutic approaches, potentially for conditions like schizophrenia.