Good Morning all and welcome to Grand Rounds here at Blogmocracy General Hospital. Today’s Grand Rounds are brought to you by the Neurology Department who remind you to mental floss at least 3 times a week.
First, let’s revisit and earlier lecture on Toxoplasma gondii which can be found at this link . Please review the previous lecture before proceeding into this lecture as we will not be re-posting redundant info such as life cycle of Toxoplasma gondii. I shall re-post the executive summary here:
Is the Crazy Cat Lady born, or do the parasites MAKE her that way?
That may seem to be more of a joke than a question. However, given new evidence about Toxoplasma gondii and mental illness actually does beg that question. You see, I have a little theory. In X amount of cases, the parasite Toxoplasma gondii may actually cause an otherwise sane female to become a Crazy Cat Lady (I know of no Crazy Cat Men, so this will be a one sided discussion), and here is how. Female buys a cat, so she is already predisposed in her mental make up to like cats. Ok, so far, so good. No problems. Lets say that this person might have just a touch of mental illness, perhaps some schizophrenia or something. But just a small non-clinical aspect of her personality that does not need to be treated and is not that important in daily living. Let’s face it, everyone is a little goofy once in awhile; that doesn’t make you mentally ill. We all have our quirks. Perhaps the parasite brings out these quirks either by chance or by design. It would be in the best interest of the parasite to have many many cats in the same place living in close proximity. This would maximize the chance of reproduction of the parasite, would it not?
Now, we shall continue with new studies and new evidence:
A microscopic parasite that breeds in cats has been found to make chimpanzees less fearful of predators in what scientists believe is further evidence that the microbe can also affect human behaviour when it infects people.
A study of Toxoplasma gondii, which is estimated to be infecting around 1,000 people every day in Britain, has found that it makes chimpanzees more attracted to the smell of leopards, their main predators in the wild.
Previous studies have shown that when the feline parasite infects mice, the rodents lose their natural fear of cats. Now the same kind of behavioural changes appear when T. gondii infects chimpanzees, the closest living relatives of humans, which usually harbour a natural fear of leopards.
The findings of the study support the controversial view that T. gondii may also influence the behaviour of infected people, possibly when it is carried in the bloodstream to the brain where it can form cysts in the amygdala, the brain region involved in fear, researchers said.
Several studies in the past have indicated that the Toxoplasma parasite can affect people’s personality by slowing down their reaction times or making them more likely to take risks. Some studies have linked the cat parasite with psychotic disturbances in humans such as self-harm and suicide, and even serious psychiatric illnesses such as schizophrenia….
“Feline species become parasitized by eating a parasitized prey. Avoidance behaviour of prey such as rodents toward feline species thus represents a natural barrier for the parasite,” Dr Poirette said.
“It has been shown, however, that T. gondii can induce behavioural change in parasitized rodents, making them more attracted to cat urine, thus benefiting parasite transmission,” she said.
“For the first time, we’ve shown that such parasite manipulation occurs in a primate, in a very specific way. We found that in our closest relative, the chimpanzee, Toxoplasma-infected animals lost their innate aversion towards leopard urine, their only natural predator,” she added.
It had been thought that if Toxoplasma, a single-cell “protozoan” parasite similar to malaria, does have an effect on human behaviour it must be a side-effect of its ability to manipulate the behaviour of other “dead end” host species such as rodents. However, the discovery that it can affect other primate species suggests a more ancient evolutionary link with humans, Dr Poirotte said.
“Our study rather supports the hypothesis that manipulative abilities of T. gondii have evolved in the human lineage when our ancestors were still under feline predation. Behavioural modifications in humans could thus be an ancestral legacy of our evolutionary past,” she said.
“Latent toxoplasmosis was commonly assumed to be asymptomatic in humans, except in pregnant women….Recent studies have shown that it could represent a risk factor for some mental disease such as schizophrenia, but more studies are needed to understand all the impacts on human health,” she added.
So, more causal links have been uncovered and are moving toward an avenue that can allow Toxoplasma gondii to find another vector in which to replicate; that vector is, in my theory, Crazy Cat Lady.
From the Original theory post some 4 years ago:
What we have here is a parasite that can manipulate the brains of rats to become less neophobic so they get eaten by the cats. This completes the life cycle of the parasite. Why couldn’t the parasite from manipulate the neural structure and chemistry of the human brain to also continue the parasite’s life cycle? I will bet that near 100% of Crazy Cat Ladies are positive for T. gondii . How many of them are acting on free will and how many are truly ill? Just something to think about next time you see a news story about a Crazy Cat Lady, perhaps she is being driven by the parasite?
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