- 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
- 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
- "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
- "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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