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saku-yu · 14 days ago

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Do you ever just,, think about the parasite that when observed in humans, has been associated with an increased risk of attempting suicide and being involved in traffic accidents?

Introducing my current (figurative) brainworm: Toxoplasma Gondii.

c/w: constant mention of suicide, some mention of parasite-induced depression, parasites

Disclaimer: I am absolutely in no way a professional in this field. This post in no way aims to act as a comprehensive medical guide, but only as a summary of some reading I have done. Some statements made may draw upon my own theories and suggestions, though I aim to keep the information mainly based around reading I have done from research papers (and I will link all sources used at the end). Some information may be incorrect, as I am no expert!

What is it?

Toxoplasma Gondii is a highly common parasite, and most of the human population are infected by it at some point in their lives.

You might’ve heard of it before, as it’s the parasite that when it infects mice, causes them to become less fearful and avoidant of the smell of a cat’s urine, and perhaps even attracted to it. This leads to the mouse approaching the cat despite the fact that doing so will get it killed. This is improtant for the parasite, as the only host in which it can sexually reproduce is the cat (or any species in the felid family). Therefore, the only way it can complete its life cycle is by infecting the cat, and to do this, can override the mouse’s whole evolutionary experience: to stay away from cats. In other words, this parasite can interfere with the mouse’s primary goal in life: to survive and carry on the mouse population, in order to favour the parasite’s own survival and life cycle!!! Over the mouse’s evolutionary characteristics!!!

Now though, get this.

In humans, infection of an individual by this parasite has been associated with a higher chance of attempting suicide!! Although this isn’t the primary symptom (so don’t worry) (infection in healthy individuals is usually asymptomatic), the thought that a parasite could induce depression and even suicidal attempts in the host is seriously so insane to me!! Though, I will discuss this later in this rant.

Another thing to mention is that the suicidal effect of infection by this parasite may only occur for a limited time. This is seen as in primary research observations, the increased risk for suicide attempts was only correlated with individuals who had the igG antibody for this parasite in their blood plasma, and was not correlated with individuals with only the igM antibody in their blood plasma.

For reference, an igG antibody is an antibody produced during an ongoing infection, whereas an igM antibody is an antibody produced during very early stages of infection.

Therefore, that suggests that the infection of an individual by this parasite only increases the individual’s risk for suicide attempts during the parasite’s ‘active state’. And its effects may diminish once the parasite reaches its ‘dormant state’. (Though this is really really tentative due to a lack of research.)

But why does it do this?

Now this is something that I can’t quite figure out, since if the parasite’s main goal (thinking using the assumption that this goal is to survive and reproduce) is only fulfilled if it can infect a feline species, how does infecting a human and increasing risk for suicide in that human aid it in fulfilling that goal?

My only idea is that perhaps this infection is an unintentional infection? As in the mechanisms and characteristics selected to aid this parasite’s survival via evolution do not aim to primarily infect and induce this effect in a human host. Now, this is a very tentative suggestion, since again, I am no professional in this field.

Following on from that idea, the fact that it is a common parasite in humans that usually causes very mild/no symptoms at all leads me to believe that it may be that this parasite and the human are two species that have faced exposure to each other over a really really long period of time, as pathogens only cause severe symptoms in a host if the two are not well acquainted, and have not adapted to show symbiosis.

How does it increase risk for suicide in an infected individual?

Aaaaaa now here’s where the results of my reading slowed considerably: there hasn’t been enough research done as of yet!!

However, it maaay be due to decreasing tryptophan (an amino acid) levels in the bloodstream of infected individuals by breaking it down to form kyneurenine. Tryptophan is a molecule required in the synthesis of serotonin, so a lack of it could potentially lead to depressive symptoms?

Again, there doesn’t really seem to be enough evidence and information yet to be able to give a fuller picture of the way it works.. so perhaps more research is needed in this field?

This may also be a good place to note that infection by this parasite is only associated with increased risk for suicide attempts, not suicide ideation, which is pretty interesting.

What implications does this have for society?

Hm, so. This leads to my main thought and the main thing that has been circling through my brain due to this topic.

Previously, I had always assumed parasite/pathogen infections to only induce physical symptoms in the host. But if mental health can potentially be directly negatively impacted by PARASITES, to me, this seems to open up many many possibilities regarding the way mental health conditions could be potentially treated and identified in the future.

This is especially notable, as some individuals with toxoplasma-induced depression do not experience an improvement in their mental health after antidepressants, but do experience an improvement after the administration of antibiotics.

Overall thoughts

Aaa this has been a reeeally long rant about the brainworm that has been making me go insane for the entirety of my today.

TLDR: Individuals infected by this parasite are more likely to attempt suicide. The exact mechanisms for this aren’t widely known.

Does this suggest more treatment options in the future and causes for mental health disorders that are not currently widely known/talked about?

Rant over, have a great day :3

References

And just better things to read if you’re interested:

The book ‘GUT’ by Julia Enders

#the bio enthusiast has a brainworm #actually going insane

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