Is a Cat Microbe Changing Your Behavior?

      In the March issue of the online edition of Atlantic Magazine is an article by Kathleen Mcauliffe entitled How Your Cat is Making You Crazy. It's about the work of Czech researcher Jaroslav Flegr, and his work with Toxoplasma gondii, the parasite associated with handling cat liter.

        Since the 1920s, doctors have warned pregnant women to avoid cat litter, since this protozoon, if transmitted to the fetus, can cause severe brain damage or death.  This microbe can also have severe effects on those with compromised immune systems.  But for healthy children and adults, the result of infection is a brief flu-like disease, and then the microbe becomes dormant inside our brain cells, and has no further effect. 

            But Flegr has begun to doubt whether it is completely dormant.   He believes that it continues to tweak our neural connections in ways that cause subtle behavioral changes. Stanford’s Robert Sapolsky believes he may be right.  Sapolsky points out that when this parasite infects a rat, it turns the rat’s natural fear of cats into an attraction to cats, which lures the rat into the jaws of its main predator, which puts the parasite inside the body of a cat, which is where it needs to be to complete its life cycle.

            And the rabies virus kills its victims, but just before it does so, it changes the victim’s brain circuits in such a way as to throw the victim into a rage, where it attacks and bites anything that moves.   By then, the virus has migrated into the saliva, so that whatever is bitten becomes the next host.   In the case of both microbes, the behavior patterns produced are quite complex—so complex that it is amazing that a microbe could evolve to accomplish this. 

            We humans are not part of the cat/rat/T. gondii cycle--we are accidental victims.  So if T. gondii causes any behavioral changes in humans at all, they would not be changes that would enhance the reproductive odds for the protozoa.  But though accidental, they may still be there.   About 20% of Americans carry the T. gondii protozoa, and according to Flegr, for their entire lives, these carriers (he happens to be one) will have their brains subtly changed. They will be changed by the accidental activity of protozoa doing what they evolved to do to make a rat’s brain force the rat to seek out cats.

            In humans, the changes which Flegr believes are wrought by this microbe are subtle, but still consistent for all carriers.  Except that in humans, the behavioral changes in human females are exactly opposite as the changes in human males.  Men who are infected tend to be more introverted, suspicious, anti-social, and oblivious to other people’s opinions of them. They are happy wearing rumpled old clothes, would prefer to work by themselves, and generally have fewer friends. Infected women tend to be outgoing, trusting, and image-conscious.  They are rule-abiding, meticulously dressed, and have a vast network of social connections.  At first, researchers could find no explanation why the behaviors of infected men and infected women seemed to be the exact opposite.   But they have concluded that there is a common denominator---emotional strain.  Women respond to insecurity by increased social bonding, and increased nurturing.   Men simply withdraw, and become more anti-social.   So we are simply seeing two sides of the same coin.

            Flegr’s data have shown (and this has been replicated) that infected individuals are much more likely to have traffic accidents.  When one considers the vast number of infected individuals worldwide (in France it’s nearly 55%) and also the number of traffic deaths, it’s possible that T.gondii is killing more people than malaria.  Flegr also has data showing that T.gondii may trigger schizophrenia in certain genetically susceptible individuals.

Check out this article: (Click on the highlighted words [Atlantic  Magazine]  above.)