Cat-to-rat-and-back parasite directly changes human brain chemistry

Common human brain parasite Toxoplasma gondii doesn’t just make rats like cats-

It works like this. The protozoan Toxoplasma comes to maturity inside a cat and the cysts are expelled in cat feces. Any cat that lives part of the time outside may be infected. The parasite doesn’t hurt the cat, however.

A rat or a mouse comes along and contacts the cat scat and the little protazoans climb aboard and migrate to the rodent’s brain but they do little damage there. The amazing thing, however, is the parasite directly manipulates their neurotransmitters (brain chemicals), especially dopamine, to cause the rat to love the smell of cats, especially their urine.

The rat hangs around in what it thinks is a wonderful place and, of course, is likely to make a nearby cat a fine meal. The parasite comes to maturity in the cat and is excreted. It makes me think of alien mind control, but that is not the end of the matter.

Many other mammals can acquire the parasite, but they are not part of the cycle. They get “secondary infections” — infections that cannot progress to completion. The effects of a secondary infection are various and not well studied, but important to wildlife, causing sickness, death and other changes.  Most of the medical attention is on infected humans who might number as many as a billion people. It doesn’t usually make people very sick. They don’t know they have it.

In humans the parasite might migrate to the eyes, the skin, or most interestingly, the brain. Toxoplasmosis is best known as a threat to pregnant women because it often causes miscarriage or birth defects. Women are told to keep away from cats, raw meat or outside gardening. Less well known is that the parasite strongly biases women to bear male babies.

It was very recently learned that in the human brain the parasite directly changes neurotransmitters like in the rat. A Stanley Medical Research Institute and Dunhill Medical Trust  research team found that the parasite causes production and release of many times the normal amount of dopamine in infected brain cells.  Dopamine helps run our brains’  pleasure center, and it affects emotions (fear, for example). Lack of dopamine production is the direct cause of Parkinson’s Disease.

It is not known if it makes people like cats, want to bring them home, adopt kitties, etc.  However, this hypothesis is reasonable, and it needs to be tested. Such behavior is certainly beneficial for the parasite’s survival.  Some tests have been done and there is a correlation between infection and certain behavioral tendencies such a jealousy in men and moralistic behavior in women. Toxoplasmosis infection is also correlated with having schizophrenia, although the direction of causation could be either direction.

Secondary infections by many kinds of parasites are often severe. In terms of Wildlife News, anti-wolf groups have instilled fear of a secondary of infection of the dog tapeworm, hydatid tapeworms, in humans. It is present the the feces of many foxes, coyotes and wolves, although these people key on the relatively rare wolf, rather than the coyote, fox or dog. Fortunately the disgusting parasite seems not to be very infectious to non-canids. Cases are few and seem not to have appeared in people who trap or professionally handle wild canids.

Photos said to be hydatid larva inside the lungs of elk might not even be correct — more likely lungworms than tapeworm larva

The message to people who worry about these things is not to kill cats, wolves, elk. It is to wash your hands when you have handled any animal or soil.  That so many do not do this is the truly amazing thing.

Print Friendly