T. gondii reproduces sexually only in cat intestines, so it manipulates intermediate hosts: infected rats lose innate aversion to cat odor, some develop fatal attraction, dose-dependently. Mechanisms under active study: the parasite produces tyrosine hydroxylase, a dopamine-pathway enzyme, and infected rodents show altered dopamine; extracellular vesicles carrying miRNAs alter neuronal gene pathways; testosterone rises. Roughly a third of humans carry latent, lifelong cysts, mostly asymptomatic. Human studies are early: altered reward modulation documented in 2017; a 2026 University of Florida preprint found infected participants showed greater cat affection, 87 percent of trial time engaging cats versus 75 percent, on a sample of two seropositive people.
The popular leap: cat ladies are parasite farms, schizophrenia links, entrepreneurship correlations, traffic-accident risk, all reported with varying strength and heavy confounding. The honest scientific position: manipulation in humans is plausible but undemonstrated at scale, and the parasite's human niche may be accidental, cats are the target, we are the collateral. The folklore version skipped the nuance years ago.
The claim: toxoplasma is the proof-of-concept that behavior can be remote-edited without the host noticing, no fever, no symptoms, just shifted preferences experienced as personality, which dissolves the last clean boundary between self and infection: your tastes may have an author that is not you. Verdict: in rodents this is simply true. In humans it is the most important unproven hypothesis in behavioral biology. The archive's note: the cat does not know about the parasite either. Both of you are the life cycle.
If a single-cell organism can edit prey behavior, what is editing yours?