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Toxoplasmosis is the name of a syndrome caused by a particularly clever protozoan parasite toxoplasma gondii that although it can affect many mammals including humans, it can only sexually reproduce in the guts of cats. However, as part of its life cycle it grows as tiny, infertile cyst cultures in the brains and nerve tissues of other mammals, producing degenerative damage. Now, for a long time it was assumed that the degenerative damage was non-adaptive, but recent findings have shown that evolutionary pressures have produced strains of toxoplasma gondii that cause infected rats to lose their fear of cats. Similarly, it causes infected cats to kill these rats and eat their brains. A convenient method for transmitting the cysts from the rat brains into the cat's guts, where they reproduce and their spores are then excreted in cat poo, to be picked up inadvertently by passing mammals, producing either direct infection, or infection through undercooked beef (using cattle as a secondary vector).
For the immunocompetent majority, it is believed to be harmless, and symptoms are usually diagnosed as a viral infection, including chills, fever, headaches and fatigue. Following these early signs, the parasite proceeds to hide from the immune system in muscle and nerve tissue causing a latent form of toxoplasmosis.
There's also the particularly nasty possibility that the parasite passes through the placenta to infect a developing human foetus. This produces mental retardation, eye disease, and hearing loss, and afflicts several tens of thousands of people annually.
People have speculated for a while on what if any behavioural effects a latent toxoplasma gondii infection would have on humans.
The manipulation hypothesis states a parasite may alter host behaviour for its own benefit, often by enhancing its transmission rate through the food chain. This paper reviews studies on the potential impact of one parasite, Toxoplasma gondii, on host behaviour, both on rodents, where altered responses may be proposed to benefit the parasite, and humans, where altered responses may arise as a side-effect of infection with no current adaptive significance.
It's pretty well established that such infections decrease reaction times, produce lethargy, and lead to an increase in traffic accidents. The authors of an Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study have a great deal to say on this topic.
The parasite Toxoplasma gondii infects 30–60% of humans worldwide. Latent toxoplasmosis, i.e., the life-long presence of Toxoplasma cysts in neural and muscular tissues, leads to prolongation of reaction times in infected subjects ... subjects with latent toxoplasmosis have significantly increased risk of traffic accidents than the non-infected subjects. Because of its high prevalence and therefore extremely high attributable mortality, latent toxoplasmosis, the mildest form of T. gondii infection, might in fact represent a serious and highly underestimated economic and public health problem.
But there's a couple of possibly nastier outcomes from the widespread, cat-induced slow plague spreading through humanity...
For nearly 30 years Dr Fuller Torrey, director of the Stanley Medical Research Institute, Maryland, USA, and his colleague Dr Robert Yolken, a Neurovirologist Professor at John Hopkins University, Baltimore, USA, have maintained that an infectious disease is the cause of schizophrenia and manic-depressive illnesses ... Early evidence for the consideration of cats as the prime cause of the disease has shown that in areas of the world where cats are common such as Germany, Ireland and Scandinavia, there is a comparatively high prevalence of schizophrenia compared to areas where they are less common, such as Papua New Guinea ... It has also been reported that individuals with first-onset schizophrenia have increased levels of antibodies to toxoplasmosis in their blood, and were readily exposed to cats during their childhood.
But perhaps the most contentious suggestion of mass-scale toxoplasma gondii human behaviour modification is the "slut theory", first hinted at in Flegr's classic page turner of operationalised psychology Changes in the personality profile of young women with latent toxoplasmosis.
Two years later, in 1999, Flegr carried out more tests, this time on a range of young women, and intended to discover exactly what the changes were. He concluded that there was a definite difference in personality profiles between the infected and uninfected individuals that he’d tested). Surprisingly, he concluded that those with latent toxoplasmosis had higher intelligence and lower guilt proneness.
the personality profiles of infected subjects differ from those of uninfected controls. These results, however, were obtained on non-standard populations (biologists or former acute toxoplasmosis patients). Here we studied the personality profiles of 191 young women tested for anti-Toxoplasma immunity during gravidity. The results showed that the differences between Toxoplasma-negative and Toxoplasma-positive subjects exits also in this sample of healthy women.
the personality profiles of women with latent toxoplasmosis differ in certain factors from those of women without toxoplasmosis. Toxoplasma-positive women have higher intelligence, guilt proneness (are more apprehensive, self-reproaching, insecure), possibly also higher ergic tension and radicalism.
The ability of toxoplasma gondii to infect a broad spectrum of mammal hosts is a very recent evolutionary development, stemming from a single lucky gene shuffling from two parental strains less than 10 KYear ago. And the adoption of the domestic cat is very recent, dating back around 10 KYear in isolated portions of the Middle East while the earliest domestic cats were seen in Europe around 400 CE. It seems that the toxoplasma gondii infection in humans is still working through its permutations.
Now Flegr's latest research (Correlation of duration of latent Toxoplasma gondii infection with personality changes in women and Decreased level of psychobiological factor novelty seeking and lower intelligence in men latently infected with the protozoan parasite Toxoplasma gondii) contends that latent toxoplasmosis effects in humans are gendered: female bodies feel a different range of physiological and psychological effects than male bodies. Something to do with dopamine sensitivities... Anyway, males tend to become withdrawn and aggressive, while females become energised, reckless, and giddy. The actual study, of course, is rather dry, so maybe it's better to let the tabloids speak for themselves...
Britain's estimated nine million domestic cats are being blamed by scientists for infecting up to half the population with a parasite that can alter people’s personalities. The figures emerge from studies into toxoplasma gondii, a parasite carried by almost all the UK's feline population and maybe elsewhere in the world. They show that half of Britain's human population carry the parasite in their brains, and that infected people may undergo slow but crucial changes in their behaviour. Infected men, suggests one new study, tend to become more aggressive, scruffy, antisocial and are less attractive. Women, on the other hand, appear to exhibit the 'sex kitten' effect, becoming less trustworthy, more desirable, fun-loving and possibly more promiscuous.
It can make women behave like "sex kittens" and men like "alley cats," the London Daily Mirror said. Women who are affected spend more on clothes and are consistently rated as more attractive, an international study has shown. They are more confident and less willing to conform to accepted moral standards. Researcher Jaroslav Flegr said: "We found they were more easy-going, more warmhearted, had more friends and cared more about how they looked. "However, they were also less trustworthy and had more relationships with men," he said. In contrast, infected men become more anti-social, suspicious and jealous, more aggressive, scruffier and less attractive to women.
Famous moggy owners include stunning Hollywood star Demi Moore, 40, who is having a passionate affair with Ashton Kutcher, 25, and pop babe Dannii Minogue, though there is no suggestion they have the bug.
Uh-huh. This is what happens when you encourage evolutionary biologists to blather on to journalists...
The apparent influence of T. gondii on the personality of human males was unexpected and pronounced. The nature of the shift in human personality following Toxoplasma infection can hardly be considered desirable. It might seem anecdotal that in a group of 29 Toxoplasma negative professors from our experimental set there are 10 present or past decision-makers (heads of department, vicedeans and deans) while among 14 Toxoplasma positive professors there is only a single head of department.
Toxoplasmosis is the name of a syndrome caused by a particularly clever protozoan parasite toxoplasma gondii that although it can affect many mammals including humans, it can only sexually reproduce in the guts of cats. However, as part of its life cycle it grows as tiny, infertile cyst cultures in the brains and nerve tissues of other mammals, producing degenerative damage. Now, for a long time it was assumed that the degenerative damage was non-adaptive, but recent findings have shown that evolutionary pressures have produced strains of toxoplasma gondii that cause infected rats to lose their fear of cats. Similarly, it causes infected cats to kill these rats and eat their brains. A convenient method for transmitting the cysts from the rat brains into the cat's guts, where they reproduce and their spores are then excreted in cat poo, to be picked up inadvertently by passing mammals, producing either direct infection, or infection through undercooked beef (using cattle as a secondary vector).
For the immunocompetent majority, it is believed to be harmless, and symptoms are usually diagnosed as a viral infection, including chills, fever, headaches and fatigue. Following these early signs, the parasite proceeds to hide from the immune system in muscle and nerve tissue causing a latent form of toxoplasmosis.
There's also the particularly nasty possibility that the parasite passes through the placenta to infect a developing human foetus. This produces mental retardation, eye disease, and hearing loss, and afflicts several tens of thousands of people annually.
People have speculated for a while on what if any behavioural effects a latent toxoplasma gondii infection would have on humans.
The manipulation hypothesis states a parasite may alter host behaviour for its own benefit, often by enhancing its transmission rate through the food chain. This paper reviews studies on the potential impact of one parasite, Toxoplasma gondii, on host behaviour, both on rodents, where altered responses may be proposed to benefit the parasite, and humans, where altered responses may arise as a side-effect of infection with no current adaptive significance.
It's pretty well established that such infections decrease reaction times, produce lethargy, and lead to an increase in traffic accidents. The authors of an Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study have a great deal to say on this topic.
The parasite Toxoplasma gondii infects 30–60% of humans worldwide. Latent toxoplasmosis, i.e., the life-long presence of Toxoplasma cysts in neural and muscular tissues, leads to prolongation of reaction times in infected subjects ... subjects with latent toxoplasmosis have significantly increased risk of traffic accidents than the non-infected subjects. Because of its high prevalence and therefore extremely high attributable mortality, latent toxoplasmosis, the mildest form of T. gondii infection, might in fact represent a serious and highly underestimated economic and public health problem.
But there's a couple of possibly nastier outcomes from the widespread, cat-induced slow plague spreading through humanity...
For nearly 30 years Dr Fuller Torrey, director of the Stanley Medical Research Institute, Maryland, USA, and his colleague Dr Robert Yolken, a Neurovirologist Professor at John Hopkins University, Baltimore, USA, have maintained that an infectious disease is the cause of schizophrenia and manic-depressive illnesses ... Early evidence for the consideration of cats as the prime cause of the disease has shown that in areas of the world where cats are common such as Germany, Ireland and Scandinavia, there is a comparatively high prevalence of schizophrenia compared to areas where they are less common, such as Papua New Guinea ... It has also been reported that individuals with first-onset schizophrenia have increased levels of antibodies to toxoplasmosis in their blood, and were readily exposed to cats during their childhood.
But perhaps the most contentious suggestion of mass-scale toxoplasma gondii human behaviour modification is the "slut theory", first hinted at in Flegr's classic page turner of operationalised psychology Changes in the personality profile of young women with latent toxoplasmosis.
Two years later, in 1999, Flegr carried out more tests, this time on a range of young women, and intended to discover exactly what the changes were. He concluded that there was a definite difference in personality profiles between the infected and uninfected individuals that he’d tested). Surprisingly, he concluded that those with latent toxoplasmosis had higher intelligence and lower guilt proneness.
the personality profiles of infected subjects differ from those of uninfected controls. These results, however, were obtained on non-standard populations (biologists or former acute toxoplasmosis patients). Here we studied the personality profiles of 191 young women tested for anti-Toxoplasma immunity during gravidity. The results showed that the differences between Toxoplasma-negative and Toxoplasma-positive subjects exits also in this sample of healthy women.
the personality profiles of women with latent toxoplasmosis differ in certain factors from those of women without toxoplasmosis. Toxoplasma-positive women have higher intelligence, guilt proneness (are more apprehensive, self-reproaching, insecure), possibly also higher ergic tension and radicalism.
The ability of toxoplasma gondii to infect a broad spectrum of mammal hosts is a very recent evolutionary development, stemming from a single lucky gene shuffling from two parental strains less than 10 KYear ago. And the adoption of the domestic cat is very recent, dating back around 10 KYear in isolated portions of the Middle East while the earliest domestic cats were seen in Europe around 400 CE. It seems that the toxoplasma gondii infection in humans is still working through its permutations.
Now Flegr's latest research (Correlation of duration of latent Toxoplasma gondii infection with personality changes in women and Decreased level of psychobiological factor novelty seeking and lower intelligence in men latently infected with the protozoan parasite Toxoplasma gondii) contends that latent toxoplasmosis effects in humans are gendered: female bodies feel a different range of physiological and psychological effects than male bodies. Something to do with dopamine sensitivities... Anyway, males tend to become withdrawn and aggressive, while females become energised, reckless, and giddy. The actual study, of course, is rather dry, so maybe it's better to let the tabloids speak for themselves...
Britain's estimated nine million domestic cats are being blamed by scientists for infecting up to half the population with a parasite that can alter people’s personalities. The figures emerge from studies into toxoplasma gondii, a parasite carried by almost all the UK's feline population and maybe elsewhere in the world. They show that half of Britain's human population carry the parasite in their brains, and that infected people may undergo slow but crucial changes in their behaviour. Infected men, suggests one new study, tend to become more aggressive, scruffy, antisocial and are less attractive. Women, on the other hand, appear to exhibit the 'sex kitten' effect, becoming less trustworthy, more desirable, fun-loving and possibly more promiscuous.
It can make women behave like "sex kittens" and men like "alley cats," the London Daily Mirror said. Women who are affected spend more on clothes and are consistently rated as more attractive, an international study has shown. They are more confident and less willing to conform to accepted moral standards. Researcher Jaroslav Flegr said: "We found they were more easy-going, more warmhearted, had more friends and cared more about how they looked. "However, they were also less trustworthy and had more relationships with men," he said. In contrast, infected men become more anti-social, suspicious and jealous, more aggressive, scruffier and less attractive to women.
Famous moggy owners include stunning Hollywood star Demi Moore, 40, who is having a passionate affair with Ashton Kutcher, 25, and pop babe Dannii Minogue, though there is no suggestion they have the bug.
Uh-huh. This is what happens when you encourage evolutionary biologists to blather on to journalists...
The apparent influence of T. gondii on the personality of human males was unexpected and pronounced. The nature of the shift in human personality following Toxoplasma infection can hardly be considered desirable. It might seem anecdotal that in a group of 29 Toxoplasma negative professors from our experimental set there are 10 present or past decision-makers (heads of department, vicedeans and deans) while among 14 Toxoplasma positive professors there is only a single head of department.
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