I always blame my behaviour on the steroids, now I've got another excuse
since I own 4 cats!
Thanks, I found it really interesting
Mel :-)
"John H" <JohnH@[EMAIL PROTECTED]
> wrote in message
news:zuqAb.11682$ws.1092924@[EMAIL PROTECTED]
> All in the mind?
>
> New Scientist vol 176 issue 2366 - 26 October 2002, page 41
>
>
> Suspicion is growing that one of the most common human parasites in the
> world is messing with our minds. James Randerson re****ts
>
>
> HAVE you been acting out of character lately? Are you having trouble
> concentrating? Don't blame late nights or old age - you might be at the
> mercy of a mind-altering parasite. A microscopic beast lying low in your
> brain may be exercising a subtle form of thought control, turning you
into
> somebody slightly different.
>
> This might sound pretty far-fetched, but evidence is growing that
Toxoplasma
> gondii - a relative of the malaria parasite - can change the way you
think.
> And you might already be infected without knowing it.
>
> Why haven't you heard any of this before? Because medical opinion
insists
> that Toxoplasma is nearly always harmless, a cause for concern only to
> pregnant women and people with a weakened immune system. The case for
the
> mind-control hypothesis is far from proven. But if it's true, the
parasite
> will become a public health nightmare overnight.
>
> Toxoplasma - or toxo as it is informally known - is one of the most
common
> human parasites in the world, infecting between 30 and 60 per cent of
the
> global population. Any mammal can be infected, but it's only in cats
that
> toxo can ***ually reproduce. It releases eggs that are spread in cat
faeces,
> and if these end up in moist soil they can remain infective for 18
months.
A
> passing rat or mouse might pick up the infection from the contaminated
soil
> and if a cat kills and eats them the life cycle continues.
>
> Toxo's danger to pregnant women comes from the parasite's ability to
cross
> the placenta and trigger a miscarriage or damage the baby's brain. But
such
> cases are fairly rare, with only a handful a year in Britain and similar
> levels in other developed countries such as the US and Australia. So
apart
> from warning prospective mothers against emptying the cat's litter tray,
> dealing with toxo has never been a public health priority.
>
> Risk factors vary between countries; most people get toxo from eating
> undercooked meat - pigs, cattle and sheep can all carry the parasite.
You
> can also catch toxo by accidentally ingesting soil traces contaminated
with
> cat faeces. So always wash your hands after doing the gardening.
>
> In the initial phase of infection, called acute toxoplasmosis, the
parasite
> is present in the blood. Typically, it causes little more than a
headache
> and sore throat, although in rare cases it can lead to serious eye
damage.
> Even if you do visit the doctor, it is almost always dismissed as a
viral
> infection.
>
> After this initial assault, the parasite hides from the immune system by
> forming resistant cysts on muscle and nerve tissue, including the brain
-
a
> stage known as latent toxoplasmosis. For most people, this disappearing
act
> is the end of the story. Once the parasite has gone to ground it almost
> never re-emerges, unless your immune system is suppressed, if you get
AIDS,
> for example. You keep the latent infection for the rest of your life -
there
> are no drugs to cure it - but the received medical wisdom is that it is
> harmless.
>
> So why the cause for concern? Well, researchers already know that toxo
can
> manipulate rodents, its natural "intermediate host". Remarkably, rats
and
> mice behave more recklessly when they are infected (see "Fatal
attraction").
> Joanne Webster and her team at Oxford University have found that the
hapless
> rodents are more active and less scared of new things. They are even
> attracted to cat urine. And research by Jaroslav Flegr and colleagues at
> Charles University in Prague has shown that rats have slowed reaction
times.
> All this makes them much more vulnerable to a feline pounce, which is
> exactly what the parasite wants. After all, toxo needs to infect a cat
(the
> "definitive host") to complete its life cycle and spread its genes.
>
> So could humans be subject to the same parasitic puppeteering? True,
toxo
> would have little evolutionary incentive to influence our actions, as
> prehistoric humans were probably not eaten by big cats often enough to
make
> it pay off. But rat and human brains are very similar. They have many of
the
> same bits and are run by the same collection of chemicals. No one really
> knows how toxo subverts rat behaviour but it's likely that it interacts
with
> a chemical in the brain. The chances are that the same substance is in
our
> brains too, so it's perfectly feasible that humans experience side
effects.
>
> Flegr and his team decided to find out if this were actually happening.
They
> carried out a series of tests on volunteers, some of whom had a latent
> infection, as revealed by antibodies to toxo in their blood.
>
> The results from personality tests were complicated and showed confusing
> gender differences, but men at least seemed to mimic one aspect of rat
> manipulation. Infected men tended to be more independent and inclined to
> break rules, although infected women tended to go the other way. Could
it
be
> that males are being made more reckless, like the rats, while for some
> reason the mind-control chemical has the opposite effect in females? At
this
> stage it's still unclear, and of course, there's not necessarily a
causal
> relation****p - certain personalities could simply be more prone to
picking
> up infections.
>
> But one test, measuring reaction times and attention span, gave more
> consistent results (Parasitology, vol 122, p 515). Both men and women
who
> had a latent infection took longer to press a computer key after a
prompt
> from the monitor. People without an infection took about 250
milliseconds
to
> react, but those with a latent infection reacted about 8 per cent
slower.
> What's more, toxo-positive subjects did worse as the experiment went on,
> suggesting that they have shorter attention spans. Again, the effects in
> humans seem to be mimicking those in rats.
>
> Until recently, few people have taken Flegr's results very seriously. So
> what if toxo causes a few strange lab results, what difference does that
> make in the real world? What made people sit up and take notice was
research
> published in August by Flegr's team showing that humans with a latent
> infection are 2.7 times more likely to be involved in a car accident
(BMC
> Infectious Diseases, www.biomedcentral.com/1471-2334/2/11).
>
> Dangerous driving
>
> The researchers tested blood samples from 146 people involved in car
crashes
> for which they were at least partly responsible, and 446 control
subjects.
> There were more toxo carriers in the "accident" group. It didn't matter
> whether the subject was a driver or a pedestrian, having the parasite
makes
> you more of a danger to other road users. Worryingly, there's an obvious
> link with Flegr's reaction time results. And if toxo slows our reaction
> times, what other effects is it having? Could it contribute to other
> trans****t accidents or industrial mishaps?
>
> Flegr's study has certainly raised eyebrows among the small group of
> specialists in the field, including some public health officials. For
> example, Richard Holliman, a parasite researcher at St George's Hospital
> Medical School in London, says that although the results need to be
> replicated: "The implications could be huge."
>
> Longer reaction times might not be the only neurological effect of toxo.
> Another controversial idea is that latent infection might trigger some
forms
> of schizophrenia. Fuller Torrey at the Stanley Medical Research
Institute
in
> Maryland and his team has found that schizophrenics are more likely to
be
> cat owners, and to have latent toxoplasmosis. What's more, drugs used to
> relieve schizophrenia symptoms happen to harm the parasite, at least in
the
> test-tube. Torrey believes this may be why the drugs work.
>
> So what should we do if it turns out that significant fractions of the
> population are infected with a parasite that slows reactions and
possibly
> causes serious mental health problems?
>
> Holliman, for one, says that we would have to consider which professions
we
> allow infected people to enter. Would we want someone with slowed
reactions
> working as an airline pilot, for example, or driving a lorry? On the
other
> hand, if we banned all infected people from jobs where fast reactions
are
> im****tant, we could lose a third of our workforce or more.
>
> In any event, toxo is unlikely to be a problem for airline pilots. The
> licensing process usually involves rigorous aptitude testing, which is
> designed to weed out anyone with chronic impairments. Tony Evans, deputy
> chief medical officer at the UK Civil Aviation Authority says: "If
you're
> performing below par, you're not going to get through the course."
>
> But what about all the other professions where reaction times matter? If
it
> turns out that latent toxoplasmosis really slows you down should bus
drivers
> or machinery operators be screened for the parasite? And if insurance
> companies decide that toxo-positive drivers are a greater risk, will
they
be
> justified in charging them higher premiums?
>
> Cutting the number of people who become infected with toxo in the first
> place is clearly an im****tant way forward. Unfortunately, the only
animal
> species for which a vaccine is available is sheep, because acute
infection
> has serious consequences for farmers. So-called "abortion storms", when
up
> to 50 per cent of ewes in a flock miscarry, occur because they're
exposed
to
> the parasite.
>
> But progress towards a human vaccine has been frustratingly slow.
> Researchers have identified components of the parasite that provide some
> protection against infection when injected into mice. But this early
work
> has stalled through lack of funding. There is not much interest in the
area
> because, although toxo is an im****tant parasite, it doesn't kill, says
> Fausto Araujo at the Palo Alto Medical Foundation in California who was
> involved in the mice studies. Perhaps if the Czech findings are
> substantiated, vaccine research will acquire a new urgency. In the
meantime,
> the only option seems to be reducing the parasite's spread through basic
> public health measures.
>
> Many people pick up toxo from undercooked meat, so better kitchen
hygiene
> and thorough cooking should go a long way to lowering infection rates.
In
a
> recent survey, Tanya Aspinall and colleagues at the University of
Manchester
> Institute of Science and Technology found that 27 of 71 meat products
from
> British supermarkets harboured toxo DNA, although they don't know if the
> parasites were viable.
>
> Holliman is adamant that tackling the parasite in meat is the best
option
> for reducing human infection. "There's no good reason why food should be
> sold with viable Toxoplasma in it," he says. On that score, keeping cat
> faeces away from animal feed is fundamental.
>
> In Britain, attitudes to the toxo public health threat vary from concern
to
> indifference, often depending on how well informed the speaker is. A
> spokesman for the British government's Department for Environment, Food
and
> Rural Affairs said officials were unaware of the studies on human
behaviour.
> But the government-funded Toxoplasma Reference Laboratory in Swansea has
> been monitoring this research. Clinical scientist Edward Guy says the
> findings aren't yet strong enough to justify action, and he is keen to
avoid
> public panic of the sort that surrounded unsubstantiated research
linking
> the MMR vaccine to autism.
>
> Down on the farm
>
> The issue has also been discussed by the government's Advisory Committee
on
> Zoonoses, which reviews the dangers posed by animal diseases that can be
> passed to humans. It is already considering what new policies would be
> needed if toxo turns out to be more dangerous than we think, or if the
> public becomes more concerned about it. One option is tighter controls
on
> farms to prevent animals picking up the parasite.
>
> The public health implications of toxo seem to be a higher priority in
> America. The US Department of Agriculture has recently commissioned a
> three-year study of beef, chicken and ****k going into the food chain to
> *****s the risk to the consumer. The researchers will analyse 6000 meat
> samples. "The study will provide the first risk *****sment of the
likelihood
> of exposure to Toxoplasma by ingesting raw or undercooked meat," a
> department spokesman says.
>
> Pigs have traditionally been thought of as the most likely animals to
pick
> up a toxo infection so the USDA is being advised by Elizabeth Wagstrom,
> director of veterinary science at the US National ****k Board, which
> represents producers. She says that US ****k infection levels are falling
> because of more intensive, indoor farming, which keeps pigs away from
cats.
> But such gains could be reversed if organic farming becomes more common.
> "It's a lot more difficult to control the parasitic disease with animals
> outside," says Wagstrom.
>
> Ultimately we'll have to wait and see if the latest findings are backed
up
> by more research. No one is suggesting drastic policy changes on the
back
of
> a handful of studies. But toxo researchers complain that the field is
being
> held back by dogma. It's hard to get funding because of the entrenched
> belief that latent toxoplasmosis is harmless. Holliman says that
alternative
> theories are seen as "too off-the-wall".
>
> Yet no one can give a good scientific reason why these effects couldn't
> occur. After all, toxo profoundly changes rodent behaviour, so why not
us
as
> well? As Joanna Webster says: "I definitely think there is something
there.
> There's no reason to think that the parasite could not manipulate
humans."
>
> Fatal attraction
>
> If you're a rat, and you like being alive, it goes without saying that
you
> don't go near cats. So it's not surprising that most rodents do a very
> effective vani****ng trick at the faintest feline whiff. But not rats
> infected with the parasite Toxoplasma gondii. In toxo-rats, the parasite
is
> calling the shots.
>
> Mice and rats pick up toxo from food that's been in contact with
> contaminated soil. But winding up in a rat is a dead end for the
microscopic
> parasite because it can only complete its ***ual cycle in a cat's guts.
> Joanne Webster and her team at Oxford University have found that toxo
has
> some tricks up its sleeve. Toxo somehow changes its host's behaviour,
making
> it more likely to finish up in a cat's stomach.
>
> Webster's team trapped wild rats - some of which were naturally infected
> with toxo - and videoed their nocturnal movements in outdoor cages. The
> infected animals were more active than the others and also more willing
to
> approach food masked with a novel smell. Both changes are hard to put
down
> simply to the rats being weakened by the infection, says Webster.
>
> But the real clincher came when the researchers offered the rats a
choice
of
> bedding - their own, or bedding laced with water, cat urine or rabbit
urine.
> Cat urine, is usually a big turn-off for rats, but the toxo-rats
actually
> preferred it.
>
> Toxo can infect every species of mammal. So can we be confident that the
> rodents are the only ones with a death wish? Although our brains are
much
> bigger, they are fundamentally very similar to a rat's. So if the
> micro-manipulators are pulling the strings there, why not in us as well?
> James Randerson
>
>
>
>
>
|
