I have an n=1 anecdata report on this topic, that some might be interested to know about.

I'd long experienced mild/moderate mental illness, including anxiety, depression, obsessiveness, sluggish cognition, possibly some ASD symptoms and possibly some personality disorder symptoms.

After my research led me to a possible link between inflammation/immunity/chronic infections and mental illness, I started attempting to influence this by adopting anti-inflammatory diets (paleo etc) and other approaches to supporting the immune system and fighting off chronic infection.

I found that at certain points, my physiological symptoms of inflammation/infection (most notably gum/tongue inflammation, digestive symptoms and tinnitus, all of which I'd had since early adolescence) would rapidly resolve, and this would be accompanied by a profound change in my mental health and sense of wellbeing: anxiety/depression would be replaced by confidence and optimism; lethargy and mental sluggishness would be replaced by physical energy, creativity, productivity and accomplishment; anger and resentment towards people in my life would be replaced by kindness and compassion; my chaotic, shambolic lifestyle would be replaced by orderliness.

However, these states of wellbeing would be accompanied by a nagging sense of fear and dread, that this version of myself wasn't the "real me", that it was unsafe for me to be in this state of health, and that I needed to go back to being my anxious, depressed, sluggish old self.

Sure enough, every time, within a few days I was back to where I was before.

It was a cycle that repeated several times over several years, during which I was torn between frustration and optimism, knowing that it was possible for me to get into a really good state of physical and mental health, but not knowing how to stay there long term.

The turning point came when I discovered and adopted a set of emotional healing practices that seek to identify and resolve deeply-held traumas and fears. I've been undertaking these practices consistently for about 6 years, and slowly but surely, my mental and physiological symptoms are steadily resolving, and all in a way that makes me feel very comfortable at every step of the process.

They're not all fully resolved yet; many of the symptoms I described above are still there to some degree, but with much less severity than when I was at my worst, and there's been a consistent enough improvement since I started this approach, that it feels like it's just a matter of time.

I'm well aware that it will take for me to achieve that state - for all symptoms of inflammation AND all symptoms of mental illness to be resolved - for my experience to be evidence of anything meaningful.

The hypothesis (which is not my own, it is from the scientist and writer whose ideas inspired me to try this approach) is that the immune system is heavily influenced by chronically held, unresolved emotions and unprocessed bad experiences.

Thus, if one is chronically stuck in a state of trauma, fear, or other negative emotion, the immune system will function in such a way that allows chronic infections to develop, leading to inflammation, which then leads to cascading effects on bodily systems including the nervous system, the hormonal system (particularly the HPA axis), the mitochondrial system and many others.

It may be because the body is devoting resources to being in a fight-or-flight state, and leaving immunity as a lower-order priority.

Or it may be that the mind/body deliberately lowers the immune system and allows these effects to happen, as a form of self-punishment (in the case of profound guilt) or to keep the self out of harm's way (a kind of trauma-induced hibernation).

I'd be unsurprised to find that either mechanism could apply depending on the preconditions, as could many others.

I raise it in the context of this article as I think it's relevant to the question of causality with respect to infections and mental health.

Given what I've experienced, it's no surprise to me to read the story of Isak McCune at the beginning of the article, in which the contraction of an infection seemed to be a trigger for serious mental illness.

But one still needs to explain why only some people who contract this infection end up with the mental illness (in Isak's case, there's no mention that the brother who'd had four bouts of strep infections had any comparable mental illness symptoms).

Equally, for many people who end up in a state of mental illness, it comes after a severe trauma or a sequence of traumatic events (one can find many studies linking PTSD with infections and inflammation). There's no need to postulate an infection as a primary cause, as we can observe the events that led the person into their state of mental illness

It makes sense to me, in theory and based on my own experience-to-date, that it is a combination of genetic preconditions, experiences, emotional states, infection exposures, immune/inflammatory responses and others, that can all conspire to result in a state of mental illness.