Wednesday, June 21, 2006

Cats Reconsidered

Ok, ok; after reading this I have to confess to feeling conflicted. I'm still a cat lover but Toxoplasma gondii seems just too intelligent by half.

On paper, Toxoplasma gondii looks as if it ought to be the most famous parasite on earth. This single-celled pathogen infects over half the world's population, including an estimated 50 million Americans. Each of Toxoplasma's victims carries thousands of the parasites, many residing in the brain. As if that were not enough of an accomplishment, Toxoplasma is equally adept at infecting all other warm-blooded animals, as disparate as chickens and kangaroos…Cats play a major role in the parasite's success. They can carry it in their intestines, where they can produce egglike cysts called oocysts. A single infected cat can shed 100 million oocysts in its droppings. The oocysts can survive in the soil for over a year and can contaminate drinking water… Once Toxoplasma enters a host, it spreads quickly. Within hours it can be detected in the heart and other organs. It is even able to infect the brain, which is protected from most pathogens by a tight barrier.

Mercifully the article notes that: “For the vast majority of people, Toxoplasma causes no serious effects.”*

So I guess the cat stays in tonight after all.

However, I’m still somewhat concerned:

For decades, most scientists believed that people with healthy immune systems had no effects from Toxoplasma. But some studies in recent years have hinted that the parasite can exert surprising effects on behavior, at least in animals. In 2000, British scientists demonstrated that rats infected with Toxoplasma lost their fear of cats. They proposed that this strategy increased the parasite's chances of getting into its final host.

I wonder if Toxoplasma leaves a certain other species of mammal altogether too inclined to forgive their cat's faults…

*Toxoplasma can be dangerous to the immuno-compromised and to unborn foetuses.

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