Toxoplasma: An Alzheimer’s-linked Parasite That Causes Rats to Be Attracted to Cats

Toxoplasma gondii is the most mind-blowing parasite that I have ever read or heard about. I was driving home when I heard this story on WBUR radio Boston and it really blew my mind. It sounded like an April Fools' science fiction joke. Now, if this doesn't disturb you, you are disturbed. Just kidding!

So here is the story as presented by WBUR Boston. The 'toxo' parasite I referenced above has a two phased life cycle. A sexual and an asexual part. The sexual part of the life cycle can only take place in the intestines of domestic or wild cats. (Felidae family). The asexual part can take place inside any warm-blooded mammals, including humans. It is the sexual part of the life cycle that gets interesting.

Typically the virus is commonly found in cat feces. When a rat eats the feces, it becomes infected (its a little disturbing that rats eat this stuff). The parasite undergoes this asexual part of its reproduction while inside the rat. Somehow in order to guarantee its survival, the parasite travels up the rat's bloodstream and into the brain. It infects the rat's amygdala (part of the brain that affects memory and emotional reactions in humans). Amazingly, this infection causes the rat to be attracted to the smell of cats. The rat basically goes looking for cats, and the lucky cat does what cats do and it gets infected. Now the 'toxo' can complete this stage of its life cycle and life goes on. I would not have believed this were it not for the reliable source. Actual scientists reported this phenomenon.

Another disturbing finding put forth by two independent teams of scientists is that infected humans are 3 to 4 times more likely to die in a car accident. On the serious side of things the virus can cause fetal deaths in humans and pregnant women are usually advised to avoid cats. The parasite is also linked to Alzheimer's disease and scientists are studying whether the domestication of the cat caused the escalation of incidence of the disease in the 19th century.