Microbes May Alter Human Behavior
‘Cat Box Disease’ May Alter Human Personality
By Roger Highfield – The Daily Telegraph 8-8-2000
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, [cat scratch fever, crazy cat lady syndrome],” but is 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 an 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 behavior 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 feline friends.
Assimilating a Host
Self-perpetuating Life-cycles
Nature contains 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 behavior, 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.
Altered Hosts
A parasite can cause various effects on it’s host, some of which are not Fully Understood.
Reproductive changes?
A recent study has indicated Toxoplasmosis correlates strongly with an increase in boy births in humans. According to the researchers, depending on the antibody concentration, the probability of the birth of a boy can increase up to a value of 0.72 … which means that for every 260 boys born, 100 girls are born. The study also notes a mean rate of 0.60 to 0.65 (as opposed to the normal 0.51) for Toxoplasma positive mothers.
Behavioral changes
It has been found that the parasite has the ability to change the behavior of its host: infected rats and mice are less fearful of cats — in fact, some of the infected rats seek out cat-urine-marked areas. This effect is advantageous to the parasite, which will be able to sexually reproduce if its host is eaten by a cat. The mechanism for this change is not completely understood, but there is evidence that toxoplasmosis infection raises dopamine levels and concentrates in the amygdala in infected mice.
The findings of behavioral alteration in rats and mice have led some scientists to speculate that toxoplasma may have similar effects in humans, even in the latent phase that had previously been considered asymptomatic. Toxoplasma is one of a number of parasites that may alter their host’s behaviour as a part of their life cycle.
The behaviors observed, if caused by the parasite, are likely due to infection and low-grade encephalitis, which is marked by the presence of cysts in the brain, which may produce or induce production of a neurotransmitter, possibly dopamine, therefore acting similarly to dopamine reuptake inhibitor type antidepressants and stimulants.
Toxoplasma’s role in psychosis?
The possibility that toxoplasmosis is one cause of schizophrenia has been studied by scientists since at least 1953. These studies had attracted little attention from U.S. researchers until they were publicized through the work of prominent psychiatrist and advocate E. Fuller Torrey. In 2003, Torrey published a review of this literature, reporting that almost all the studies had found that schizophrenics have elevated rates of toxoplasma infection. A 2006 paper has even suggested that prevalence of toxoplasmosis has large-scale effects on national culture. These types of studies are suggestive but cannot confirm a causal relationship (because of the possibility, for example, that schizophrenia increases the likelihood of toxoplasma infection, rather than the other way around).
Acute Toxoplasma infection sometimes leads to psychotic symptoms not unlike schizophrenia. Some anti-psychotic medications that are used to treat schizophrenia, such as Haloperidol, also stop the growth of Toxoplasma in cell cultures. Several studies have found significantly higher levels of Toxoplasma antibodies in schizophrenia patients compared to the general population. Toxoplasma infection causes damage to astrocytes in the brain, and such damage is also seen in schizophrenia.
- Decreased novelty-seeking behaviour
- Slower reactions
- mental illness
- Drug abuse
- Suicide
- Lower rule-consciousness and jealousy (in men)
- More warmth and conscientiousness (in women)
- Majoring in business
- Starting a business
- A growing list of other possible issues
Not Entirely Scientific Method
There have been no randomized clinical trials studying the effects of toxoplasma on human behavior. Although some researchers have found potentially important associations with toxoplasma, it is possible that these associations merely reflect factors that predispose certain types of people to infection (e.g., people who exhibit risk-taking behaviors may be more likely to take the risk of eating undercooked meat). The evidence for behavioral effects on humans is relatively weak. Although dubious, studies continue to produce results published in various journals, and disseminated into the public at large.
Ongoing Studies
Other studies continue suggest that the parasite may influence personality. There are claims of toxoplasma causing antisocial attitudes in men and promiscuity (or even “signs of higher intelligence”) in women, and greater susceptibility to schizophrenia and manic depression in all infected persons. A 2004 study found that toxoplasma “probably induce[s] a decrease of novelty seeking.”
Toxoplasma infections lead to changes depending on the sex of the infected person. According to Sydney University of Technology infectious disease researcher Nicky Boulter in an article that appeared in the January/February 2007 edition of Australasian Science magazine.
The study suggests that male carriers:
- Have lower IQs
- Tend to achieve a lower level of education
- Have shorter attention spans
- Greater likelihood of breaking rules and taking risks
- Are more independent, anti-social, suspicious, jealous and morose
- It also suggests that these men are deemed less attractive to women
Women carriers are suggested to be:
- Higher intelligence
- More outgoing
- More friendly
- More promiscuous
- Are considered more attractive to men compared with non-infected controls
More Car Accidents?
Studies have found that toxoplasmosis is associated with an increased car accident rate, roughly doubling or tripling the chance of an accident relative to uninfected people. This may be due to the slowed reaction times that are associated with infection. “If our data are true then about a million people a year die just because they are infected with toxoplasma,” the researcher Jaroslav Flegr told The Guardian. The data shows that the risk decreases with time after infection, but is not due to age. Ruth Gilbert, medical coordinator of the European Multicentre Study on Congenital Toxoplasmosis, told BBC News Online these findings could be due to chance, or due to social and cultural factors associated with toxoplasma infection. However there is also evidence of a delayed effect which increases reaction times.
More than 60 million people in the United States may carry the parasite, the centers for disease control said, often after contact with raw meat or cat feces.
Cat feces parasite may alter human brains to reduce fear
The bravery needed to start that business might he buried in a cat’s litterbox. A parasite found in cat feces may alter human minds to make us less fearful,“ a new study has found.
The parasite, Toxoplasma gondii, infects an estimated 2 billion people worldwide. It also appears to shift the behavior of rodents, making them unafraid of cats, University of Colorado researchers theorized the bug” may affect humans similarly, making them more open to risk in business, for example.
White more research is needed, they did find relations. People at entrepreneurial events who carried the parasite were nearly twice as likely as other attendees to have started their own businesses, while college students who picked up the bug were 4 times more likely to major in business. The study, led by associate professor Stefanie Johnson, was published recently in the Proceedings of the Royal Society.
T. gondii has been tied to increased risks of “car accidents, mental illness, neuroticism, drug abuse and suicide,” the researchers wrote, according to NBC ’ News. Past studies suggest it alters brain chemistry and behavior, particularly around dopamine; the chemical linked to pleasure.
More than 60 niillion people in the United States may carry the parasite, the Centers for Disease Control said, often after contact with raw meat or cat feces. It’s often unnoticeable, as human immune systems usually ward off symptoms.
In rodents with the parasite, the lack of fear around cats makes them more likely to be eaten. That works out well for the parasite, which reproduces once inside the cat. So what might it do in humans? Researchers tested about 1,500 students and about 200 attendees of entrepreneurial events to find Whether they had carried. T. gondii. 22% (Twenty-two percent) tested positive in all, NBC 7 News notes. Researchers also dove into databases from 42 different countries, per Sky News, Comparing infection data with entrepreneurial activity, they concluded that “infection prevalence was a consistent, positive predictor of entrepreneurial activity” at the national level.
Clearly much of this research is speculative if not sensationalist journalism which may all suffer from confirmation bias in extremes. Foremost in question is the concept that that there is even such a thing as normal behavior, to finally asking what definitive and absolute influence the parasite actually does have on human behavior or that of any other type of hosts. Keeping in mind other correlations such as running a business, studying psychology, marketing and art has also been contended by certain studies to require inherently sociopathic tendencies. Studies such as these will probably go on until a vaccine and treatment for toxoplasmosis or human behavior is discovered. Of course, be warned taking measures to avoid infection especially by any parasite is advisable, where even without changing behavior as a factor this disease and others can be dangerous, if not potentially deadly, for some.