Unchained Metaphor

A year and a half ago or so, I was trying to claw my way out of a major depressive episode. "Double depression," they call it when someone with dysthymia descends into a major depression. The language here, by the way, is absolutely unsatisfactory: major depression ("major depressive episode") is not, in my experience a more significant or "major" issue than dysthymia. This despite what the usual sources have to say on the matter: The Mayo Clinic calls dysthymia "a mild, but chronic, form of depression." To their credit, they do go on to say, "Although dysthymia symptoms may be less intense than those of depression, dysthymia can actually affect your life more seriously because it lasts for so long." And even that understates the destruction dysthymia causes in the lives of those who suffer from it.  More commonly, I read that dysthymia is "less severe" than major depression.  It is true that someone in a major depressive episode is more severely hobbled by the disease than is someone suffering from dysthymia. But, as the Mayo Clinic  suggests, and as my experience confirms, over the long term dysthymia is the more debilitating condition.

But I digress.
I do that sometimes.

Anyway, I was crawling out of the major depression, struggling just to return to the alienating unhappiness that seems to be my "normal," and I began thinking of depression as a parasite. Not literally, of course. But when thinking of my own experiences with depression and with dysthymia I began to see that parasitism could be a useful metaphor.

I try to explain myself after the jump. . .



As a way of explaining, in my usual roundabout way, let me start with the zombie ant fungus. You probably have heard of this.  If not, that Wiki link will provide plenty of details. Briefly, however, spores enter the ant's body and begin to affect the brain. The ant, its behavior driven by the spores, will climb up the stalk of a plant, fix its mandibles into the plant, and then die. Some days later the fungus breaks out of the ant's head, releasing spores that drift down to infect other ants on the forest floor.

Dead "Zombie ant" with spore-filled fruiting body emerging from head. Image from Questionable Evolution

Those ants will then repeat the narrative: climb up a stalk, die, and release the fungus that rains down again.

One more case: Toxoplasmosis, which is caused by a protozoan parasite that is common in cats. Of particular relevance is its effect on mice and rats: when infected, they become less fearful of cats, and in some cases are attracted to the scent of cat urine. Now, being attracted to places where cats hang out clearly is not recommended behavior for tasty little rodents; but having the rodent seek out cat urine is very good for the parasite: rodents that do this, driven by their infections, are more likely to be eaten. The cat that eats the rodent then becomes a carrier, spreading the  protozoan to offspring and through fecal contamination (Yes, that includes litterboxes; some speculation suggests the protozoan might affect the behavior of humans as well as rats, but these claims remain controversial).

In each of these cases the important idea is this: the parasite changes the behavior of the host in ways that are beneficial to the parasite and detrimental to the host. There are other examples: The hairworm infects grasshoppers,  and causes them to jump into water, where the worm reproduces. The rabies virus makes its host produce more saliva AND makes the host more aggressive: when the host bites another mammal, the virus spreads. More examples in this Scientific American paper (pdf).

OK, by now you are wondering: what does any of this have to do with depression?

Imagine a parasite, a virus perhaps or a bacteria or a protozoan—it doesn't matter— that feeds on human sadness.  There is a pretty compelling sci-fi story here for someone to take up. This parasite thrives when its host is miserable, suicidal, alone and hopeless. It devours despair. The more the host suffers, the more the parasite reproduces. Like the parasites in the examples above, this parasite has evolved to change the behavior of its host in ways that maximize despair. 

Alright, honestly, I have no idea where I'm going with this. But maybe I can sort it out in a paragraph or two.

Imagine a parasite that feeds on sadness. It creates that sadness by changing behavior. The first step for the parasite might be simple: cause a slight sadness in the person who is the host. This causes the  person to withdraw from other human contact, to be distracted from important work or studies. It might cause tension in a relationship. It might lead the person so infected to eat carb-laden food (Ben and Jerry's, anyone!). The person might no longer have the incentive or energy to exercise. All of these things are KNOWN to worsen depression. So the depression worsens. The parasite reproduces more, becomes stronger. As the despair deepens, the host maybe loses his/her job; a significant other leaves; the host begins drinking too much. Friends drift away. The person has fewer friends, no significant other, no job. Hopelessness dominates; thought processes become negative. And all this, too,  exacerbates depression. It is a vicious cycle. And escaping it can seem impossible: the depressed person needs to stay with a regimen if he/she is to escape: needs to take pills on schedule, needs to get sunlight, needs to exercise, needs to spend more time socializing. But the very depression, the very parasite, that these things can alleviate, makes it impossible to do these things. The parasite has taken total control: your entire existence has no other function other than to feed the parasite with your deepening hopelessness; and as you feed it, it only deepens the hopelessness.  You are like the ant or the mouse: driven toward a goal that serves only the parasite, a goal that is all too likely to prove fatal.

And here the metaphor breaks down: in the case of the ant, the fungus can reproduce only after the ant dies. But the depression parasite needs us to stay alive so that we can stay depressed. In this aspect the best metaphor may be other parasites: ones like malaria, that do not necessarily kill the host.  (technically speaking, if it is generally non-lethal it is a  parasite; if it must kill the host, as in the case of the zombie ant fungus, it is a parasitoid.)

Anyway, what I came here to say is: depression is like a parasite that feeds on despair and that changes human behavior in ways that maximize the despair it needs to survive. Am I making sense yet??

OK. I'll work more on this. In the meantime, here is some bonus audio-visual: a nice little clip on the zombie ant fungus, with some amazing images of species-specific varieties....