Mind Control Parasites in Half of All Humans

iiii writes "According to a Yahoo News story, half of the world's human population is infected with Toxoplasma, a parasite shown to alter the brain function of rats, inducing them into behavior that benefits the parasite but is suicidal for the rat. So what affect does it have on humans? Article comes complete with Heinlein 'Puppet Masters' reference. I call dibs on using Toxoplasma as a name for my rock band."

Comments

Re:Welcome...

[packeteer]

http://www.guardian.co.uk/life/thisweek/story/0,12 977,1048642,00.html

Dated Thursday September 25, 2003

Ive read that these parasited are more common in the UK or perhaps we only know of more cases there becuase people are looking harder. Im not exactly an expert on the topic but i know this has been "news" for years now.

Re:Welcome...

[alicenextdoor]

Toxoplasma gondii is a protozoan which has cats as its definitive host. It has a wide range of intermediate hosts, and is capable of infecting all warm-blooded vertebrates, including humans. Toxoplasma lives inside the epithelial cells lining the intestine of its feline host. Eggs are shed with the faeces, and can survive in soil for several months. Toxoplasma cells can also penetrate work their way out of the intestine and infect almost any other cell type, eventually forming cysts in the host's brain, liver and muscles. Intermediate hosts are infected either by eating food or water contaminated with infected cat faeces; by eating undercooked meat from other intermediate hosts containing Toxoplasma cysts; or, in the case of some unfortunates, via the placenta from an infected mother.

Back to the rats. Rats are easily infected with Toxoplasma, and have been the subject of a lot of experimentation. Infection tends to lead to the establishment of Toxoplasma cysts in the brain, and alteration of the rat's behaviour. Infected rats tend to be more active and less afraid of novelty, both of which behaviours are likely to place the rat at increased risk of predation by cats. The changes go further than that, however. Rats are inherently, and understandably, afraid of the odour of cats. Even lab rats which have not been exposed to cats for generations will avoid areas marked with cat urine. Toxoplasma infected rats do not, however, share this aversion; in fact, rats tested in pens marked with different types of scent (rat urine, cat urine, rabbit urine and water) actually seemed to be suicidally attracted to the cat-scented areas . The infected rats appeared to be completely healthy in all other ways .

The implications of this research are enough to send a frisson of fear down the spine of anyone, devoted parasitologist or otherwise. Toxoplasma infection is common amongst humans. It has been estimated that 30% of the global human population may be infected, with prevalence in specific countries ranging from 22% in the UK to 84% in France. Can the parasite affect human behaviour in the way in which it affects that of rats? The answer appears to be "yes". One manner in which this happens is via direct damage to the host's brain and central nervous system. Babies born to mothers infected with Toxoplasma early in fetal development can suffer from widespread disease, including mental retardation . Infection later in development can lead to a persistant infection with no apparent symptoms, with the parasite forming cysts in the brain. With any luck the immune system can keep the parasite under control; depression of the immune system, however, can result in its reactivation, with consequent neurological or psychiatric effects.

It has also been suggested that prenatal exposure to toxoplasmosis can increase an individual's susceptibility to schizophrenia , but because of the difficulty of experimenting in this area, there is little supporting evidence , although it is interesting to note that several of the drugs used in the treatment of schizophrenia and bipolar disorder inhibit the replication of Toxoplasma . Does the manipulation hypothesis hold in humans? If it does, it must be only as a non-adaptive side effect of the ability to manipuate hosts such as mice and rats, since, as Joanne Webster points out in a fascinating review article on the subject , humans are rarely preyed upon by cats. There does appear to be some evidence that human personality traits are affected by Toxoplasma infection, but the one study that has specifically looked for an effect is less than wholly convincing. Flegr and Hrdý, found that men with chronic Toxoplasma infections had a greater tendency to disregard rules and were more suspecting, jealous and dogmatic than non-infected controls . However, the number of males tested was only 195, of whom 56 were infected, and the effect disappeared entirely if the male and female subjects were analyzed together. This research provides a fascinating, if somewhat disturbing, hint of an effect, but it seems safe to say that most of us are more than mere parasite-controlled robots.