'Cat Box Disease' May
Change Human Personality
And Lower IQ
By Roger Highfield - The Daily Telegraph
LONDON - Scientists have discovered a parasite that inhabits rats and makes them feel a suicidal attraction for cats. The parasite, which infects as many as one in five rats, can also affect humans.
The parasite, nicknamed the love bug but scientifically known as Toxoplasma gondii, an intracellular protozoan, infects the rodent's brain, inducing an effect similar to Prozac so it becomes less fearful of cats.
Once the infected rat is eaten by the cat, the parasite is successfully transmitted to its definitive host, which ensures the completion of the parasite's life cycle.
Humans may also be influenced by the parasite, which is transmitted through eating raw infected meat or contact with cat feces, according to the latest issue of Royal Society's Proceedings: Biological Sciences.
"We believe that these results may explain the reports of altered personality and IQ levels in some humans," said Dr. Manuel Berdoy, who made the discovery along with Joanne Webster, a doctor, and David Macdonald, a professor.
"Although we clearly represent a dead-end host for the parasite, these symptoms represent the outcome of a parasite evolved to manipulate the behaviour of another mammal," Dr. Berdoy said.
In Britain, 22% of the population have been found to be host to the parasite. The problem is worse in France, where the infection rate is up to four times higher.
Although speculative, Dr. Webster said other work had linked the parasite to decreased IQ, hyperactivity and altered personality profiles.
"Perhaps you can see a side effect in other hosts," Dr. Webster said, adding it was not known if the bug encouraged people to be fond of their felines.
Nature contains other bizarre examples of mind control by parasitic invaders. Dr. William Eberhard, of the Smithsonian Tropical Research Institute in Costa Rica, described a wasp living inside a spider.
The parasitic wasp larva spends two weeks inside the live spider, feeding on its body fluids. When the wasp is ready to pupate, the spider builds a web consisting of a few lines that support a central platform from which the wasp will eventually hang in a cocoon. Dr. Eberhard believes the larva produces a drug inducing its host to weave the supportive web, before killing and eating the spider.
One classic example of this kind of mind control concerns Dicrocoelium dendriticum, the lancet liver fluke parasite that inhabits the bile duct of cattle.
The parasite's eggs are released in cattle feces, where they are ingested by a land snail. Once inside a snail, the parasite then develops into a stage called cercaria, eventually released in mucus "slime balls" on vegetation.
There the parasite gains entry into a second host, the ant Formica fusca, which dines on slime balls. Within the ant, most of the parasites head for the abdomen but a few make for the head, where they tinker with the ant's behaviour, causing it to commit suicide.
When the temperature drops as evening approaches, infected ants do not return to their nests. Instead, they climb atop grass blades and other vegetation.
The ants wait to be eaten by browsing cattle, which prefer to eat late in the evening or in the early morning. Then the parasite's life cycle is completed.

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