What would make a rat think it could take on cat? Scientists have discovered that a certain microbe, Toxoplasma gondii (tocks-oh-plaz-ma gone-dee-ee), causes rats to lose their typical fear and avoidance behavior. It also makes them act hyperactive, which makes it more likely that they’ll attract a passing cat's attention.
Infected rats make easy cat snacks
Why would a microbe cause its host to act suicidal?
T. gondii is a parasitic protozoan. Parasites are basically creatures that mooch off others. Parasite protozoa are microscopic moochers. They often have very complex lives, moving among many hosts and environments. In the case of T. gondii, the cat is its ultimate host. That is, the only place the parasite can reproduce sexually is in cats’ guts. T. gondii does not seem to cause any illness or harm to cats.
On the other hand, rats, other mammals and birds are in-between hosts. The protozoan reproduces in these hosts by repeatedly dividing in two. T. gondii can cause illness if the host’s immune defenses are weakened.
This is the life cycle of T. gondii. It reproduces sexually inside a cat's body. Early-stage cells called oocysts (oh-oh-sists) are formed and passed out of the cat’s body with its feces. The oocysts develop into mature cells. Animals such as mice or pigs pick up the mature cells when they touch, sniff or eat tiny bits of cat feces. The protozoan cells invade the animals’ cells and rapidly multiply by repeatedly dividing in two. The protozoan returns to cats when the hungry felines eat infected animals, usually mice or rats.
People can become infected by T. gondii if they eat undercooked meat from infected animals, although this isn't common. Litterboxes are another source of infection. People may unwittingly breathe in oocysts on dust churned up by the process of changing used litter. Makes you get a little squeamish, doesn’t it? Fortunately, healthy people usually fight off T. gondii infections very well. Some surveys have suggested that up to 40 percent of people have been infected with T. gondii and didn't even know it. Nor does being infected by T. gondii make us want to pick fights with cats.
However T. gondii can cause serious infections in infants in the womb. That’s why pregnant women are often urged to avoid any contact with litterboxes.
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