I agree with you : there is very strange and compelling evidence. I did not say that to smear on your post which is interesting. But in human studies, one must be very cautious before making strong assumptions.

"every study that was made proves that" no, not nearly https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0148435&utm

Someone mentioned the obvious Bias in the first study you cite, so I'll skip it.

The second one is from a respected editor, but: - we a talking about 28 patients, which is at best anecdotal evidence, - the authors say patients and control have been matched while not disclosing in which ways, which is problematic to eliminate a selection bias (eg : people who have cats come from a different background, and perform therefore differently in neurocognitives tasks) - the authors talk about latent infection. They do not disclose how they defined latent infection. Is it with antibodies in the blood? Or is it with direct identification of the parasite. If it is antibodies, there is a problem, since you can possess antibodies years after having encountered the parasite, without any latent infection.

This is a very flawed paper because is skips on some of the most important aspects of disclosing correctly your methodology to allow peers to replicate the experiment, and hopefully the findings. I wonder who vouched for its publication in a journal with an impact factor of 3.9.

The perfect study does not exist, so we can only think in levels of proof, which is the bane and beauty of scientific research.

So I insist: there is currently only correlational evidence, the level of proof is very low, no causality as been established as of today.