How Your Cat Is Making You Crazy
(トキソプラズマ)(弓形蟲感染症)
Jaroslav Flegr is no kook. And yet, for years, he suspected his mind had
been taken over by parasites that had invaded his brain. So the
prolific biologist took his science-fiction hunch into the lab. What
he’s now discovering will startle you. Could tiny organisms carried by
house cats be creeping into our brains, causing everything from car
wrecks to schizophrenia?
N
o one would accuse
Jaroslav Flegr of being a conformist. A self-described “sloppy
dresser,” the 53-year-old Czech scientist has the contemplative air of
someone habitually lost in thought, and his still-youthful, square-jawed
face is framed by frizzy red hair that encircles his head like a ring
of fire.
Certainly
Flegr’s thinking is jarringly unconventional. Starting in the early
1990s, he began to suspect that a single-celled parasite in the
protozoan family was subtly manipulating his personality, causing him to
behave in strange, often self-destructive ways. And if it was messing
with his mind, he reasoned, it was probably doing the same to others.
The parasite, which is excreted by cats in their feces, is called
Toxoplasma gondii (T. gondii or Toxo
for short) and is the microbe that causes toxoplasmosis—the reason
pregnant women are told to avoid cats’ litter boxes. Since the 1920s,
doctors have recognized that a woman who becomes infected during
pregnancy can transmit the disease to the fetus, in some cases resulting
in severe
brain damage or death.
T. gondii is also a major threat to people with weakened immunity: in the early days of the AIDS
epidemic, before good antiretroviral drugs were developed, it was to
blame for the dementia that afflicted many patients at the disease’s end
stage. Healthy children and adults, however, usually experience nothing
worse than brief flu-like symptoms before quickly fighting off the
protozoan, which thereafter lies dormant inside brain cells—or at least
that’s the standard medical wisdom.
But
if Flegr is right, the “latent” parasite may be quietly tweaking the
connections between our neurons, changing our response to frightening
situations, our trust in others, how outgoing we are, and even our
preference for certain scents. And that’s not all. He also believes that
the organism contributes to car crashes, suicides, and mental disorders
such as schizophrenia. When you add up all the different ways it can
harm us, says Flegr, “Toxoplasma might even kill as many people as malaria, or at least a million people a year.”
An
evolutionary biologist at Charles University in Prague, Flegr has
pursued this theory for decades in relative obscurity. Because he
struggles with English and is not much of a conversationalist even in
his native tongue, he rarely travels to scientific conferences. That
“may be one of the reasons my theory is not better known,” he says. And,
he believes, his views may invite deep-seated opposition. “There is
strong psychological resistance to the possibility that human behavior
can be influenced by some stupid parasite,” he says. “Nobody likes to
feel like a puppet. Reviewers [of my scientific papers] may have been
offended.” Another more obvious reason for resistance, of course, is
that Flegr’s notions sound an awful lot like fringe science, right up
there with UFO sightings and claims of dolphins telepathically
communicating with humans.
But
after years of being ignored or discounted, Flegr is starting to gain
respectability. Psychedelic as his claims may sound, many researchers,
including such big names in neuroscience as Stanford’s Robert Sapolsky,
think he could well be onto something. Flegr’s “studies are well
conducted, and I can see no reason to doubt them,” Sapolsky tells me.
Indeed, recent findings from Sapolsky’s lab and British groups suggest
that the parasite is capable of extraordinary shenanigans. T. gondii,
reports Sapolsky, can turn a rat’s strong innate aversion to cats into
an attraction, luring it into the jaws of its No. 1 predator. Even more
amazing is how it does this: the organism rewires circuits in parts of
the brain that deal with such primal emotions as fear, anxiety, and
sexual arousal. “Overall,” says Sapolsky, “this is wild, bizarre
neurobiology.” Another academic heavyweight who takes Flegr seriously is
the schizophrenia expert E. Fuller Torrey, director of the Stanley
Medical Research Institute, in Maryland. “I admire Jaroslav for doing
[this research],” he says. “It’s obviously not politically correct, in
the sense that not many labs are doing it. He’s done it mostly on his
own, with very little support. I think it bears looking at. I find it
completely credible.”
What’s more, many experts think T. gondii
may be far from the only microscopic puppeteer capable of pulling our
strings. “My guess is that there are scads more examples of this going
on in mammals, with parasites we’ve never even heard of,” says Sapolsky.
Familiar
to most of us, of course, is the rabies virus. On the verge of killing a
dog, bat, or other warm-blooded host, it stirs the animal into a rage
while simultaneously migrating from the nervous system to the creature’s
saliva, ensuring that when the host bites, the virus will live on in a
new carrier. But aside from rabies, stories of parasites commandeering
the behavior of large-brained mammals are rare. The far more common
victims of parasitic mind control—at least the ones we know about—are
fish, crustaceans, and legions of insects, according to Janice Moore, a
behavioral biologist at Colorado State University. “Flies, ants,
caterpillars, wasps, you name it—there are truckloads of them behaving
weirdly as a result of parasites,” she says.
Consider Polysphincta gutfreundi,
a parasitic wasp that grabs hold of an orb spider and attaches a tiny
egg to its belly. A wormlike larva emerges from the egg, and then
releases chemicals that prompt the spider to abandon weaving its
familiar spiral web and instead spin its silk thread into a special
pattern that will hold the cocoon in which the larva matures. The
“possessed” spider even crochets a specific geometric design in the net,
camouflaging the cocoon from the wasp’s predators.
Flegr himself
traces his life’s work to another master of mind control. Almost 30
years ago, as he was reading a book by the British evolutionary
biologist Richard Dawkins, Flegr was captivated by a passage describing
how a flatworm turns an ant into its slave by invading the ant’s nervous
system. A drop in temperature normally causes ants to head underground,
but the infected insect instead climbs to the top of a blade of grass
and clamps down on it, becoming easy prey for a grazing sheep. “Its
mandibles actually become locked in that position, so there’s nothing
the ant can do except hang there in the air,” says Flegr. The sheep
grazes on the grass and eats the ant; the worm gains entrance into the
ungulate’s gut, which is exactly where it needs to be in order to
complete—as the Lion King song goes—the circle of life. “It was
the first I learned about this kind of manipulation, so it made a big
impression on me,” Flegr says.
After
he read the book, Flegr began to make a connection that, he readily
admits, others might find crazy: his behavior, he noticed, shared
similarities with that of the reckless ant. For example, he says, he
thought nothing of crossing the street in the middle of dense traffic,
“and if cars honked at me, I didn’t jump out of the way.” He also made
no effort to hide his scorn for the Communists who ruled Czechoslovakia
for most of his early adulthood. “It was very risky to openly speak your
mind at that time,” he says. “I was lucky I wasn’t imprisoned.” And
during a research stint in eastern Turkey, when the strife-torn region
frequently erupted in gunfire, he recalls being “very calm.” In
contrast, he says, “my colleagues were terrified. I wondered what was
wrong with myself.”
His
bewilderment continued until 1990, when he joined the biology faculty
of Charles University. As it happened, the 650-year-old institution had
long been a world leader in documenting the health effects of
T. gondii,
as well as developing methods for detecting the parasite. In fact, just
as Flegr was arriving, his colleagues were searching for infected
individuals on whom to test their improved diagnostic kits, which is how
he came to be asked one day to roll up his sleeve and donate blood. He
discovered that he had the parasite—and just possibly, he thought, the
key to his baffling self-destructive streak.
He delved into T. gondii’s
life cycle. After an infected cat defecates, Flegr learned, the
parasite is typically picked up from the soil by scavenging or grazing
animals—notably rodents, pigs, and cattle—all of which then harbor it in
their brain and other body tissues. Humans, on the other hand, are
exposed not only by coming into contact with litter boxes, but also, he
found, by drinking water contaminated with cat feces, eating unwashed
vegetables, or, especially in Europe, by consuming raw or undercooked
meat. Hence the French, according to Flegr, with their love of steak
prepared
saignant—literally, “bleeding”—can have infection rates
as high as 55 percent. (Americans will be happy to hear that the
parasite resides in far fewer of them, though a still substantial
portion: 10 to 20 percent.) Once inside an animal or human host, the
parasite then needs to get back into the cat, the only place where it
can sexually reproduce—and this is when, Flegr believed, behavioral
manipulation might come into play.
Researchers had already observed a few peculiarities about rodents with
T. gondii
that bolstered Flegr’s theory. The infected rodents were much more
active in running wheels than uninfected rodents were, suggesting that
they would be more-attractive targets for cats, which are drawn to
fast-moving objects. They also were less wary of predators in exposed
spaces. Little, however, was known about how the latent infection might
influence humans, because we and other large mammals were widely
presumed to be accidental hosts, or, as scientists are fond of putting
it, a “dead end” for the parasite. But even if we were never part of the
parasite’s life cycle, Flegr reasoned, mammals from mouse to man share
the vast majority of their genes, so we might, in a case of mistaken
identity, still be vulnerable to manipulations by the parasite.
In
the Soviet-stunted economy, animal studies were way beyond Flegr’s
research budget. But fortunately for him, 30 to 40 percent of Czechs had
the latent form of the disease, so plenty of students were available
“to serve as very cheap experimental animals.” He began by giving them
and their parasite-free peers standardized personality tests—an
inexpensive, if somewhat crude, method of measuring differences between
the groups. In addition, he used a computer-based test to assess the
reaction times of participants, who were instructed to press a button as
soon as a white square popped up anywhere against the dark background
of the monitor.
The
subjects who tested positive for the parasite had significantly delayed
reaction times. Flegr was especially surprised to learn, though, that
the protozoan appeared to cause many sex-specific changes in
personality. Compared with uninfected men, males who had the parasite
were more introverted, suspicious, oblivious to other people’s opinions
of them, and inclined to disregard rules. Infected women, on the other
hand, presented in exactly the opposite way: they were more outgoing,
trusting, image-conscious, and rule-abiding than uninfected women.
The
findings were so bizarre that Flegr initially assumed his data must be
flawed. So he tested other groups—civilian and military populations.
Again, the same results. Then, in search of more corroborating evidence,
he brought subjects in for further observation and a battery of tests,
in which they were rated by someone ignorant of their infection status.
To assess whether participants valued the opinions of others, the rater
judged how well dressed they appeared to be. As a measure of
gregariousness, participants were asked about the number of friends
they’d interacted with over the past two weeks. To test whether they
were prone to being suspicious, they were asked, among other things, to
drink an unidentified liquid.
The results meshed well with the
questionnaire findings. Compared with uninfected people of the same sex,
infected men were more likely to wear rumpled old clothes; infected
women tended to be more meticulously attired, many showing up for the
study in expensive, designer-brand clothing. Infected men tended to have
fewer friends, while infected women tended to have more. And when it
came to downing the mystery fluid, reports Flegr, “the infected males
were much more hesitant than uninfected men. They wanted to know why
they had to do it. Would it harm them?” In contrast, the infected women
were the most trusting of all subjects. “They just did what they were
told,” he says.
Why men
and women reacted so differently to the parasite still mystified him.
After consulting the psychological literature, he started to suspect
that heightened anxiety might be the common denominator underlying their
responses. When under emotional strain, he read, women seek solace
through social bonding and nurturing. In the lingo of psychologists,
they’re inclined to “tend and befriend.” Anxious men, on the other hand,
typically respond by withdrawing and becoming hostile or antisocial.
Perhaps he was looking at flip sides of the same coin.
Closer
inspection of Flegr’s reaction-time results revealed that infected
subjects became less attentive and slowed down a minute or so into the
test. This suggested to him that Toxoplasma might have an adverse
impact on driving, where constant vigilance and fast reflexes are
critical. He launched two major epidemiological studies in the Czech
Republic, one of men and women in the general population and another of
mostly male drivers in the military. Those who tested positive for the
parasite, both studies showed, were about two and a half times as likely
to be in a traffic accident as their uninfected peers.
When I met Flegr
for the first time, last September, at his office on the third floor of
Charles University’s Biological Sciences building, I was expecting
something of a wild man. But once you get past the riotous red hair, his
style is understated. Thin and slight of build, he’s soft-spoken,
precise with his facts, and—true to his Toxo status—clad in old
sneakers, faded bell-bottom jeans, and a loose-fitting button-up shirt.
As our conversation proceeds, I discover that his latest findings have
become—to quote Alice in Wonderland—“curiouser and curiouser,”
which may explain why his forehead has the deep ruts of a chronic
worrier, or someone perpetually perplexed.
He’s published some
data, he tells me, that suggest infected males might have elevated
testosterone levels. Possibly for that reason, women shown photos of
these men rate them as more masculine than pictures of uninfected men.
“I want to investigate this more closely to see if it’s true,” he says.
“Also, it could be women find infected men more attractive. That’s
something else we hope to test.”
Meanwhile, two Turkish studies have replicated his studies linking Toxoplasma to traffic accidents. With up to one-third of the world infected with the parasite, Flegr now calculates that T. gondii
is a likely factor in several hundred thousand road deaths each year.
In addition, reanalysis of his personality-questionnaire data revealed
that, just like him, many other people who have the latent infection
feel intrepid in dangerous situations. “Maybe,” he says, “that’s another
reason they get into traffic accidents. They don’t have a normal fear
response.”
It’s almost impossible to hear about Flegr’s research
without wondering whether you’re infected—especially if, like me, you’re
a cat owner, favor very rare meat, and identify even a little bit with
your Toxo sex stereotype. So before coming to Prague, I’d gotten
tested for the parasite, but I didn’t yet know the results. It seemed a
good time to see what his intuition would tell me. “Can you guess from
observing someone whether they have the parasite—myself, for example?,” I
ask.
“No,”
he says, “the parasite’s effects on personality are very subtle.” If,
as a woman, you were introverted before being infected, he says, the
parasite won’t turn you into a raving extrovert. It might just make you a
little less introverted. “I’m very typical of Toxoplasma males,”
he continues. “But I don’t know whether my personality traits have
anything to do with the infection. It’s impossible to say for any one
individual. You usually need about 50 people who are infected and 50 who
are not, in order to see a statistically significant difference. The
vast majority of people will have no idea they’re infected.”
Still,
he concedes, the parasite could be very bad news for a small percentage
of people—and not just those who might be at greater risk for car
accidents. Many schizophrenia patients show shrinkage in parts of their
cerebral cortex, and Flegr thinks the protozoan may be to blame for
that. He hands me a recently published paper on the topic that he
co-authored with colleagues at Charles University, including a
psychiatrist named Jiri Horacek. Twelve of 44 schizophrenia patients who
underwent MRI scans, the team found, had reduced gray matter in the
brain—and the decrease occurred almost exclusively in those who tested
positive for T. gondii. After reading the abstract, I must look
stunned, because Flegr smiles and says, “Jiri had the same response. I
don’t think he believed it could be true.” When I later speak with
Horacek, he admits to having been skeptical about Flegr’s theory at the
outset. When they merged the MRI results with the infection data,
however, he went from being a doubter to being a believer. “I was amazed
at how pronounced the effect was,” he says. “To me that suggests the
parasite may trigger schizophrenia in genetically susceptible people.”
One
might be tempted to dismiss the bulk of Flegr’s work as hokum—the
fanciful imaginings of a lone, eccentric scholar—were it not for the
pioneering research of Joanne Webster, a parasitologist at Imperial
College London. Just as Flegr was embarking on his human trials,
Webster, then a freshly minted Ph.D., was launching studies of Toxo-infected
rodents, reasoning, just as Flegr did, that as hosts of the parasite,
they would be likely targets for behavioral manipulation.
She
quickly confirmed, as previous researchers had shown, that infected rats
were more active and less cautious in areas where predators lurk. But
then, in a simple, elegant experiment, she and her colleagues
demonstrated that the parasite did something much more remarkable. They
treated one corner of each rat’s enclosure with the animal’s own odor, a
second with water, a third with cat urine, and the last corner with the
urine of a rabbit, a creature that does not prey on rodents. “We
thought the parasite might reduce the rats’ aversion to cat odor,” she
told me. “Not only did it do that, but it actually increased their
attraction. They spent more time in the cat-treated areas.” She and
other scientists repeated the experiment with the urine of dogs and
minks, which also prey on rodents. The effect was so specific to cat
urine, she says, that “we call it ‘fatal feline attraction.’”
She
began tagging the parasite with fluorescent markers and tracking its
progress in the rats’ bodies. Given the surgically precise way the
microbe alters behavior, Webster anticipated that it would end up in
localized regions of the brain. But the results defied expectations. “We
were quite surprised to find the cysts—the parasite’s dormant form—all
over the brain in what otherwise appeared to be a happy, healthy rat,”
she says. Nonetheless, the cysts were most abundant in a part of the
brain that deals with pleasure (in human terms, we’re talking sex,
drugs, and rock and roll) and in another area that’s involved in fear
and anxiety (post-traumatic stress disorder affects this region of the
brain). Perhaps, she thought, T. gondii uses a scattershot approach, disseminating cysts far and wide, enabling a few of them to zero in on the right targets.
To
gain more clarity on the matter, she sought the aid of the
parasitologist Glenn McConkey, whose team at the University of Leeds was
probing the protozoan’s genome for signs of what it might be doing. The
approach brought to light a striking talent of the parasite: it has two
genes that allow it to crank up production of the neurotransmitter
dopamine in the host brain. “We never cease to be amazed by the
sophistication of these parasites,” Webster says.
Their
findings, reported last summer, created immediate buzz. Dopamine is a
critical signaling molecule involved in fear, pleasure, and attention.
Furthermore, the neurotransmitter is known to be jacked up in people
with schizophrenia—another one of those strange observations about the
disease, like its tendency to erode gray matter, that have long puzzled
medical researchers. Antipsychotic medicine designed to quell
schizophrenic delusions apparently blocks the action of dopamine, which
had suggested to Webster that what it might really be doing is thwarting
the parasite. Scientists had already shown that adding the medicine to a
petri dish where T. gondii is happily dividing will stunt the
organism’s growth. So Webster decided to feed the antipsychotic drug to
newly infected rats to see how they reacted. Lo and behold, they didn’t
develop fatal feline attraction. Suddenly, attributing behavioral
changes to the microbe seemed much more plausible.
As
the scientific community digested the British team’s dopamine
discoveries, Robert Sapolsky’s lab at Stanford announced still more
attention-grabbing news. The neuroscientist and his colleagues found
that T. gondii disconnects fear circuits in the brain, which
might help to explain why infected rats lose their aversion to cat odor.
Just as startling, reports Sapolsky, the parasite simultaneously is
“able to hijack some of the circuitry related to sexual arousal” in the
male rat—probably, he theorizes, by boosting dopamine levels in the
reward-processing part of the brain. So when the animal catches a whiff
of cat scent, the fear center fails to fully light up, as it would in a
normal rat, and instead the area governing sexual pleasure begins to
glow. “In other words,” he says, “Toxo makes cat odor smell sexy to male rats.”
The
neurobiologist Ajai Vyas, after working with Sapolsky on this study as a
postdoctoral student, decided to inspect infected rats’ testicles for
signs of cysts. Sure enough, he found them there—as well as in the
animals’ semen. And when the rat copulates, Vyas discovered, the
protozoan moves into the female’s womb, typically infecting 60 percent
of her pups, before traveling on up to her own brain—creating still more
vehicles for ferrying the parasite back into the belly of a cat.
Could T. gondii
be a sexually transmitted disease in humans too? “That’s what we hope
to find out,” says Vyas, who now works at Nanyang Technological
University, in Singapore. The researchers also discovered that infected
male rats suddenly become much more attractive to females. “It’s a very
strong effect,” says Vyas. “Seventy-five percent of the females would
rather spend time with the infected male.”
After I return from
Prague, Flegr informs me that he’s just had a paper accepted for
publication that, he claims, “proves fatal feline attraction in humans.”
By that he means that infected men like the smell of cat pee—or at
least they rank its scent much more favorably than uninfected men do.
Displaying the characteristic sex differences that define many Toxo traits,
infected women have the reverse response, ranking the scent even more
offensive than do women free of the parasite. The sniff test was done
blind and also included urine collected from a dog, horse, hyena, and
tiger. Infection did not affect how subjects rated these other samples.
“Is
it possible cat urine may be an aphrodisiac for infected men?,” I ask.
“Yes. It’s possible. Why not?” says Flegr. I think he’s smiling at the
other end of the phone line, but I’m not sure, which leaves me wondering
whether I’ve stumbled onto a topic ripe for a Saturday Night Live
skit, or a matter worthy of medical concern. When I ask Sapolsky about
Flegr’s most recent research, he says the effects Flegr is reporting
“are incredibly cool. However, I’m not too worried, in that the effects
on humans are not gigantic. If you want to reduce serious car accidents,
and you had to choose between curing people of Toxo infections versus getting people not to drive drunk or while texting, go for the latter in terms of impact.”
In fact, Sapolsky thinks that Toxo’s
inventiveness might even offer us some benefits. If we can figure out
how the parasite makes animals less fearful, he says, it might give us
insights into how to devise treatments for people plagued by
social-anxiety disorder, phobias, PTSD, and the like. “But frankly,” he
adds, “this mostly falls into the ‘Get a load of this, can you believe what nature has come up with?’ category.”
Webster
is more circumspect, if not downright troubled. “I don’t want to cause
any panic,” she tells me. “In the vast majority of people, there will be
no ill effects, and those who are affected will mostly demonstrate
subtle shifts of behavior. But in a small number of cases, [Toxo
infection] may be linked to schizophrenia and other disturbances
associated with altered dopamine levels—for example,
obsessive-compulsive disorder, attention-deficit hyperactivity disorder,
and mood disorders. The rat may live two or three years, while humans
can be infected for many decades, which is why we may be seeing these
severe side effects in people. We should be cautious of dismissing such a
prevalent parasite.”
The psychiatrist E. Fuller Torrey
agrees—though he came to this viewpoint from a completely different
angle than either Webster or Flegr. His opinion stems from decades of
research into the root causes of schizophrenia. “Textbooks today still
make silly statements that schizophrenia has always been around, it’s
about the same incidence all over the world, and it’s existed since time
immemorial,” he says. “The epidemiology literature contradicts that
completely.” In fact, he says, schizophrenia did not rise in prevalence
until the latter half of the 18th century, when for the first time
people in Paris and London started keeping cats as pets. The so-called
cat craze began among “poets and left-wing avant-garde Greenwich Village
types,” says Torrey, but the trend spread rapidly—and coinciding with
that development, the incidence of schizophrenia soared.
Since the 1950s, he notes, about 70 epidemiology studies have explored a link between schizophrenia and T. gondii.
When he and his colleague Robert Yolken, a neurovirologist at Johns
Hopkins University, surveyed a subset of these papers that met rigorous
scientific standards, their conclusion complemented the Prague group’s
discovery that schizophrenic patients with Toxo are missing gray
matter in their brains. Torrey and Yolken found that the mental illness
is two to three times as common in people who have the parasite as in
controls from the same region.
Human-genome studies, both
scientists believe, are also in keeping with that finding—and might
explain why schizophrenia runs in families. The most replicated result
from that line of investigation, they say, suggests that the genes most
commonly associated with schizophrenia relate to the immune system and
how it reacts to infectious agents. So in many cases where the disease
appears to be hereditary, they theorize, what may in fact be passed down
is an aberrant or deficient immune response to invaders like T. gondii.
Epstein-Barr
virus, mumps, rubella, and other infectious agents, they point out,
have also been linked to schizophrenia—and there are probably more as
yet unidentified triggers, including many that have nothing to do with
pathogens. But for now, they say, Toxo remains the strongest
environmental factor implicated in the disorder. “If I had to guess,”
says Torrey, “I’d say 75 percent of cases of schizophrenia are
associated with infectious agents, and Toxo would be involved in a significant subset of those.”
Just
as worrisome, says Torrey, the parasite may also increase the risk of
suicide.
In a 2011 study of 20 European countries, the national suicide
rate among women increased in direct proportion to the prevalence of the
latent Toxo infection in each nation’s female population. According to
Teodor Postolache, a psychiatrist and the director of the Mood and
Anxiety Program at the University of Maryland School of Medicine, a
flurry of other studies, several conducted by his own team, offers
further support of T. gondii’s link to higher rates of suicidal
behavior. These include investigations of general populations as well as
groups made up of patients with bipolar disorder, severe depression,
and schizophrenia, and in places as diverse as Turkey, Germany, and the
Baltimore/Washington area. Exactly how the parasite may push vulnerable
people over the edge is yet to be determined. Postolache theorizes that
what disrupts mood and the ability to control violent impulses may not
be the organism per se, but rather neurochemical changes associated with
the body’s immune response to it. “As far-fetched as these ideas may
sound,” says Postolache, “the American Foundation for Suicide Prevention
was willing to put money behind this research.”
Given all the nasty science swirling around this parasite, is it time for cat lovers to switch their allegiance to other animals?
Even
Flegr would advise against that. Indoor cats pose no threat, he says,
because they don’t carry the parasite. As for outdoor cats, they shed
the parasite for only three weeks of their life, typically when they’re
young and have just begun hunting. During that brief period, Flegr
simply recommends taking care to keep kitchen counters and tables wiped
clean. (He practices what he preaches: he and his wife have two
school-age children, and two outdoor cats that have free roam of their
home.) Much more important for preventing exposure, he says, is to scrub
vegetables thoroughly and avoid drinking water that has not been
properly purified, especially in the developing world, where infection
rates can reach 95 percent in some places. Also, he advises eating meat
on the well-done side—or, if that’s not to your taste, freezing it
before cooking, to kill the cysts.
As concerns about the latent
infection mount, however, experts have begun thinking about
more-aggressive steps to counter the parasite’s spread. Inoculating cats
or livestock against T. gondii might be one way to interrupt its
life cycle, offers Johns Hopkins’ Robert Yolken. Moving beyond
prevention to treatment is a taller order. Once the parasite becomes
deeply ensconced in brain cells, routing it out of the body is virtually
impossible: the thick-walled cysts are impregnable to antibiotics.
Because T. gondii and the malaria protozoan are related, however,
Yolken and other researchers are looking among antimalarial agents for
more-effective drugs to attack the cysts. But for now, medicine has no
therapy to offer people who want to rid themselves of the latent
infection; and until solid proof exists that Toxo is as dangerous as some scientists now fear, pharmaceutical companies don’t have much incentive to develop anti-Toxo drugs.
Yolken hopes that will change. “To explain where we are in Toxo
research today,” he says, “the analogy I always give is the ulcer
bacteria. We first needed to find ways of treating the organism and
showing that the disease went away when you did that. We will have to
show that when we very effectively treat Toxoplasma, some portion of psychiatric illness goes away.”
But T. gondii
is just one of an untold number of infectious agents that prey on us.
And if the rest of the animal kingdom is anything to go by, says
Colorado State University’s Janice Moore, plenty of them may be capable
of tinkering with our minds. For example, she and Chris Reiber, a
biomedical anthropologist at Binghamton University, in New York,
strongly suspected that the flu virus might boost our desire to
socialize. Why? Because it spreads through close physical contact, often
before symptoms emerge—meaning that it must find a new host quickly. To
explore this hunch, Moore and Reiber tracked 36 subjects who received a
flu vaccine, reasoning that it contains many of the same chemical
components as the live virus and would thus cause the subjects’ immune
systems to react as if they’d encountered the real pathogen.
The
difference in the subjects’ behavior before and after vaccination was
pronounced: the flu shot had the effect of nearly doubling the number of
people with whom the participants came in close contact during the
brief window when the live virus was maximally contagious. “People who
had very limited or simple social lives were suddenly deciding that they
needed to go out to bars or parties, or invite a bunch of people over,”
says Reiber. “This happened with lots of our subjects. It wasn’t just
one or two outliers.”
Reiber has her eye trained on other human
pathogens that she thinks may well be playing similar games, if only
science could prove it. For example, she says, many people at the end
stages of AIDS and
syphilis express an intense craving for sex. So, too, do individuals at
the beginning of a herpes outbreak. These may just be anecdotal
accounts, she concedes, but based on her own findings, she wouldn’t be
surprised if these urges come from the pathogen making known its will to
survive.
“We’ve found all kinds of excuses for why we do the
things we do,” observes Moore. “‘My genes made me do it.’ ‘My parents
are to blame.’ I’m afraid we may have reached the point where parasites
may have to be added to the laundry list of excuses.”
She has a point. In fact, I’ve been wondering whether T. gondii
might in some small way be contributing to my extreme extroversion—why I
can’t resist striking up conversations everywhere I go, even when I’m
short of time or with strangers I’ll never see again. Then it occurs to
me that cysts in my brain might be behind my seesaw moods or even my
splurges on expensive clothes. Maybe, I think with mounting conviction,
the real me would have displayed better self-control, had I not been
forced to swim upstream against the will of an insidious parasite. With
my feline pal Pixie on my lap (for the record, she’s an outdoor cat), I
call to get the results of my Toxo test. Negative. I don’t have the latent infection.
I
call to tell Flegr the good news. Even though I’m relieved, I know my
voice sounds flat. “It’s strange to admit,” I say, “but I think I’m a
little disappointed.” He laughs. “People who have cats often feel that
way, because they think the parasite explains why they behave this way
or that,” he says. “But,” I protest, “you thought the same way.” Then it
hits me. I may have dodged
T. gondii, but given our knack for
fooling ourselves—
plus all those parasites out there that may also be
playing tricks on our minds—can anyone really know who’s running the
show?
https://www.theatlantic.com/magazine/archive/2012/03/how-your-cat-is-making-you-crazy/308873/
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How do Parasites Hijack their Host's Brains? The Neuroscience of Toxoplasmosis(弓形蟲感染症)
https://faculty.washington.edu/chudler/toxo.html
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トキソプラズマが人の脳を操る仕組み
http://natgeo.nikkeibp.co.jp/nng/article/news/14/7449/
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起業したい人は猫のウ●コ食べればできるかも！（良い子は真似しないように、危険です）
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[大阪]野良猫への餌やりから口論となり、同じマンションに住む男性をカッターで切りつけ。(2015/06)
[東京]野良猫に餌をあげ、隣人に注意された事に怒り果物ナイフで切りつけ。(2015/05)
[福岡]「野良猫に餌をやるな」と注意されて激怒し、57歳男性の顔面を殴る。(2014/11)
[静岡]よく公園で餌やりしていた犯人が、市主導で野良猫駆除を行っていた男性の胸倉を掴みカッターで脅す。(2011/03)
[船橋]女性から野良猫の餌やりを注意され、その帰宅を待ち伏せして包丁で刺殺。(2009/08)
[川崎]アパートの大家に餌やりを注意され逆上、大家を刺殺し義理の娘にも重症を負わせる。(2008/06)
[大阪]猫被害の苦情を言いに来たアパートの隣人を包丁で刺す。(2007/07)
[尼崎]猫の餌付けに苦情を言った人の部屋へ包丁を持って押し込み乱闘に。(2005/04)
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猫オタのロリコン勝又拓哉が2005年栃木県今市市で下校途中の７歳の女児を車で拉致して
わいせつ行為をしたあとに胸をメッタ刺しにして殺害して雑木林に遺棄した残虐な事件
勝又拓哉の飼っていた希少種の猫の毛が女児の遺体の付着していたことが逮捕の決め手
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猫オタが起こした猟奇殺人事件「神戸小1女児バラバラ殺害事件」
猫オタのロリコン君野康弘が2014.年に神戸市長田区で6歳の女児を家に連れ込んで
殺害してわいせつ行為をした後に遺体をバラバラにしてビニール袋に入れて遺棄した残虐な事件
君野康弘は飼ってる猫を餌に猫好き女児を家に連れ込んでいた 勝又被告、控訴審も有罪 今市事件で東京高裁
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2005年12月、日光市（旧今市市）大沢小1年だった吉田有希ちゃん=当時（7）=が殺害された
今市事件で、殺人罪に問われた鹿沼市西沢町、無職勝又拓哉被告（36）の控訴審判決公判が
3日午前、東京高裁で開かれた。藤井敏明裁判長は、無期懲役を言い渡した一審宇都宮地裁の
裁判員裁判判決を破棄したが、被告に無期懲役を言い渡した。
https://headlines.yahoo.co.jp/hl?a=20180803-03057321-soon-l09
