Common Parasite May Trigger Suicide Attempts

[Sir Patrick Crocodile]

Originally Posted by Glob

What do you mean?

I mean, that there are problems which could make them unhappy in the first place. Get rid of these problems first. If they are just plain depressed, quite possibly such a parasite could induce depression. I presume this is what the article is trying to get at, though I haven't read the whole thing.

Originally Posted by Glob

I'd certainly eat my words in a second if this was achieved.

Hence the word "probably" here. Having had experience at the attempts level, I'd certainly be surprised if that would work as well.

[Glob]

Originally Posted by Crocodile

I mean, that there are problems which could make them unhappy in the first place. Get rid of these problems first.

This is what I am suggesting.

Originally Posted by Crocodile

If they are just plain depressed, quite possibly such a parasite could induce depression. I presume this is what the article is trying to get at, though I haven't read the whole thing.

I think it highly unlikely that there is a causal relationship between T. gondii and suicidal tendencies. I think that a suicidal person will, in almost all (or all) cases, be suicidal regardless of whether or not they have the parasite.

If they can at least show that the suicidal tendencies start some time after the parasite enters the body, I will think again.

[Xeno]

In relation to this, I am recollecting the utter certainty with which it was accepted by modern science, and I mean in the last fifty years, that stomach ulcers were stress related and needed dietary and lifestyle changes, rather than something to kill the actual causative thing. After the new understanding of cause, all sorts of old views about causes and relationships collapsed. Thinking changed.

Of course I recognise that here we are talking about a contributory or partial factor rather than an entire cause. I am not dismissing the new information lightly though. We may need to think somewhat differently about depression rather than simply saying, "yes, but all the old information still stands".

[Darwinsbulldog]

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001661/

Toxoplasmosis is already known to affect mental states, including confusion, and with immunocompromised people, can cause death. Infected people have 7 times the likelhood of experiencing suicidal ideation is an empirical fact, according to this study:-

In our study we found that if you are positive for the parasite, you are seven times more likely to attempt suicide."

Thus Toxo cannot be ruled out as a contributory cause with the information we have so far. Correlation does not prove causation. Nevertheless, the is enough of a smoking gun for more scientific studies.

And whether or not Toxo causes or contributes towards suicide, the other known effects of infection indicate that treatment to remove the parasite is a good idea.

[Neospora]

Hmm, might need to change my avatar byline then? Nah, I retain my friendliness

(Neospora is the canine/bovine equivalent of the feline/ovine Toxoplasma. There are subtle genetic differences, but there are many who believe that they should be classified as different species within the same genus, Toxoplasma)


As has been mentioned, this study has noted a correlation, and doesn't infer a causal relationship. However, I think it is quite feasible that infections with this parasite (which has a predilection for encysting in the brain) has an effect on brain chemistry that might influence a person's susceptibility to act on suicidal ideation. Toxo has been shown to influence behaviour in humans, and is known to alter the behaviour of rats and mice. Toxo infected rats and mice do not recognise cat urine as a deterrent, start to emerge in daylight, amongst other behavioural changes. This is 'engineered' by the parasite to make it more likely for the rodent to be caught by a cat, and eaten, thus completing the lifecycle in the feline definitive host. Infected humans apparently become more promiscuous and indulge in risk-taking behaviours: http://www.abc.net.au/catalyst/stories/s2050191.htm (linky to a friend's research that was featured on Catalyst) also here for a trashier version.

The problem with 'ridding' a person of the parasite is that it encysts in the brain, where many drugs cannot effectively reach it. Inside the cysts are dormant 'bradyzoites'. It is a eukaryotic organism, and is obligately intracellular so there aren't as many drugs that will be parasiticidal that won't also have nasty side effects for the human cells. Current therapy involves sulfadiazine and pyrimethamine, or atovaquone, or clindamycin. These are aimed at mopping up active 'tachyzoites', parasites that spontaneously emerge from ruptured cysts, before they can cause too much damage. The parasite is also fond of skeletal and cardiac muscle, and the spinal cord. The immune system in a healthy human can usually stop the tachyzoites from dividing out of control, but in immunocompromised hosts this doesn't happen, so drug prophylaxis is required for the rest of their lives. In the past in HIV patients, Toxoplasma encephalitis was a common cause of death.

Basically, once you have it, you've got it for life. If testing people with depression for the presence of Toxoplasma can identify those more at risk of suicide, then perhaps making the patient aware of the link could help take the risk back to the same as an uninfected person? I don't think many people, suicidal or not, would like to think that a parasite in their brain is controlling their behaviour. Cognitive behaviour therapy already uses awareness and self analysis for treatment, so there is precendent.

Off for a proper read, wondering if schizophrenia is identified as a factor. Delusional parasitosis with a basis in fact maybe?

[Darwinsbulldog]

Nice to have a published biologist comment on this subject, thanks Neospora!

[AndyP]

Originally Posted by Glob

This is bullshit IMO. People attempt suicide because they are unhappy, not because they have some inflammation of the brain due to a parasite. If you want to find out whether people are at risk of suicide, find out how unhappy they are. If you want to help prevent them from taking their lives, help them to get happy; don't waste time trying to rid them of some parasite.

I have had 4 mates commit suicide. 3 local showed no signs of unhappiness. The other was Mackay (I am in Brisbane) so I cant comment on her state of mind

[BlueDevil]

The article shows a correlation between Toxoplasma gondiis and suicide. This of course doesn’t prove one causes the other. However when you consider the two main options it does certainly raise the possibility that Toxo may be involved in causing suicide. So maybe Toxo causes suicidal ideation, or suicidal ideation causes Toxo to be present. The latter seems quite unlikely. Maybe there are other explanations for the reason these two factors co-exist?

The fact that Toxo results in inflammation which is thought to be the cause of brain cell damage is also quite plausible. Inflammation has been found to be a major causative factor in a number of medical conditions. The link between inflammation and asthma has been recognised for some time now, but in years gone by wasn’t even considered as a factor. More recently it has been realised that inflammation plays a significant role in coronary artery disease. If you had suggested that heart attacks were caused by inflammation in the past people probably would have thought you were a nutter. Then of course there was the discovery by two Australian doctors that peptic ulcers were most commonly caused by a bacterial infection that lead to inflammation. Prior to that it was thought that ulcers were caused by stress and dietary factors like acidic or spicy foods. The guys who proposed this idea were laughed at, but had the last laugh when they were awarded the Nobel Prize for their work in this area. I have no doubt that inflammation will be implicated in many more medical conditions.

Originally Posted by Glob

This is bullshit IMO. People attempt suicide because they are unhappy, not because they have some inflammation of the brain due to a parasite. If you want to find out whether people are at risk of suicide, find out how unhappy they are. If you want to help prevent them from taking their lives, help them to get happy; don't waste time trying to rid them of some parasite.

This research sounds interesting and to me seems quite plausible. It is obviously too early to claim a definite link but it certainly warrants further research. It certainly raises the possibility of treatment strategies if it does turn out that Toxo is one of the causes of suicidal ideation.

[Darwinsbulldog]

In my Endnotes database I have plenty of papers linking parasites to altered behaviour in their hosts. Not specifically about the Toxo-Homo link, but in many other taxa. I will dig them out when I have a spare moment.

There seems to be a conspiricy, even amoungst some evolutionary biologists, to down-play the effects of parasites on their hosts. And yet profound effects from behaviour modification to speciation and parthenogenesis is well documented.

[Sir Patrick Crocodile]

Like Cordyceps fungus, DBD?

I would think it has more to do with a chemical which alters behaviour, generated by the parasite.