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toxoplasma gondii & human behavior manipulation!!!

V.Z.Nuri vznuri at yahoo.com
Fri Jan 4 11:11:27 EST 2002

summary: warning!! toxoplasma gondii parasite 
may be altering *mass*human*behavior* in widespread, malicious,
dangerous, possibly even *suicidal* ways!!! (references at bottom)

hi all. recently I read the book "parasite rex"
by carl zimmer. very excellent info on parasites,
but also very eye opening as far as new perspectives
on evolution & the environment relative to
parasites. the scientific community is going through
various paradigm shifts re: parasites as
documented in this book.

one very important chapter covers the manipulation
of host behavior by parasites via infiltration into
the nervous system of the host. this happens in
several identified cases in extremely sophisticated
ways. its also clear some parasites can taylor its strategy
for multiple intermediate hosts.. in a sense they
"know" which host in their chain they are in and
can affect each one accordingly.

what shocked me about the book was info on the
parasite *toxoplasma*gondii*, treated somewhat nonchalantly 
by the author & scientists, but that has me extremely
concerned when I did further research and
looked into "connecting the dots". t.gondii is in *billions*
of humans by some estimates (30-50% of *all*humans* 
by some estimates). 

t.gondii is the reason pregnant
women are advised not to clean cat litter boxes. cats
are referred to as a "definitive host" where the
parasite can complete its cycle and 
can reproduce *sexually*. however the
parasite can reproduce *asexually* in other species
such as rats. 

rat behavior manipulation!!

in rats, the parasite alters behavior such that the
rats become less "novelty fearing" and may even
*seek out* cat smells. i.e. a "rodent kamakazes"
with suicidal urges. this makes *predation* by a
cat host more likely, and the parasite jumps from
the killed rat to the predatory cat during the "carnivorism".

what is really concerning me is how little is
known about toxoplasma gondii in *humans*. its
not very much studied possibly largely because there
seems to be a conventional wisdom that it is
harmless/benign and the cat is the "preferred host".
but I am very skeptical!! I find it unlikely
billions of infected humans are a mere *coincidence*
and that the human is a "dead end" (more conventional
wisdom) for the parasite.

only within the last few years was the "rodent kamakaze"
discovery made!!! it was big media news in 2000, you
can find these articles on the web. I have sent
email to joanne webster and j.flegr, two key 
scientists in the area. webster worked with the
rat experiments. both have written articles suggesting
that the parasite needs to be taken more seriously
by the scientific community because of its implications
to human epidemiology!!

human behavioral manipulation!!

j.flegr is possibly one of only a few scientists in
the world looking at psychological effects in the
*human* by t.gondii. his papers in the mid 90s
did find a *manipulation* of human behavior, slightly
different in females than males. human females become 
more social, males become more expedient/less moral.
(along with other subtle shifts).

currently these behavioral changes in 
humans are postulated as mere side
effects of t.gondii mechanisms for manipulating
rats. I dont believe it!! especially after reading
zimmer, it is clear that some parasites have highly
specific behaviors tailored to each host.

apparently t.gondii can be spread in a *congenital*
form from human mother to embryo. imho this needs to
be seen for what it is: a *reproduction* 
and *transmission* of the
parasite to a new host, i.e. another human!!

note!! scientists are also recently
implicating toxoplasma gondii in human mental 
disorders such as schizophrenia
and bipolar disorders!!

the hypothesis: humans as a key intermediate host, *not* a dead end!!

here I want to propose something very radical, that
existing t.gondii scientists are highly dismissive of, and
probably too conservative to even consider or mention.
a scientific hypothesis that the human is not
merely a "incidental" host for t.gondii but in
fact an important *intermediate* host, such that
t.gondii has a means of moving among humans or
out of humans into the other carriers (rats, cats, ..?)

the present scientists consider such a scenario not
only unlikely but laughable!! flegr has a slide of
a big jungle cat attacking a hunter with a gun, and
both he and webster write about how "carnivorism of humans by cats
is rare". 

I smell a rat!! a blind spot!! where is
the scientific evidence that humans are a dead end???
what is the possibility that we may not have yet mapped
out all of t.gondii's transmission pathways, and that
there are ways for it to move out of humans & continue
its cycle??

my main conjecture (apparently not being proposed or
pursued by *anyone* currently studying t.gondii, from
my recent search): that t.gondii can get out of
humans back into its main cycle.. somehow..!!

it is apparently known/established that t.gondii *cannot* 
be transmitted in human waste, one of its mechanisms of
exiting the cat. however I am not aware of any scientific
evidence that suggests there are no pathways whatsoever out
of the human into other species. even if impossible, as
is apparently the assumption, this needs to be 
proved/established/ruled out scientifically!!

extrapolation: human behavior alteration *enhances*transmission*!!

it is natural to next consider that the human behavioral
alterations help *enhance*transmission* of the parasite, the
next key hypothesis. I dont want to be too specific, but
let's consider some possible scenarios not totally ridiculous
based on current knowledge.

one possibility is the behavior changes in humans mean
they are more likely to adopt cats!! there is some support for
this in flegr's studies; this requires some way for 
cats to be infected from humans.  (it is easy to argue the
direction goes from cat to human and never vice versa). 
 such a pathway is not currently known, but again, 
I dont believe it can be ruled out either.

suppose that human women who are infected are more likely
to have sex, or more likely to have babies. if the t.gondii
can be propagated this way, then it is to its advantage
to actually cause this host behavior manipulation!!

another idea that has occured to me while considering
this line of inquiry. scientists are baffled why the parasite
would have opposite effects on human male vs. female
psychology, and use this divergence as evidence that the
behavior modification may be meaningless in the human.

however, consider (along the above line of thinking)
that the parasite may be propagated to
*different hosts* based on whether it is in human males
or females. it is natural to assume the baby is the next
carrier for females, but what about males?

the battlefield possibility!!

one possibility, I dont think can be scoffed at: consider
that maybe t.gondii can be carried into rats via their
eating *human*corpses*!! the modern hygienic standards of
carefully quarantining human bodies has not persisted
throughout our human history. in particular, it is natural
to wonder if rats pick up the parasite from *human*graveyards*
via contact with the corpses!!

this led me to wonder: what about *human*battlefields*?
our history teaches us these have been vastly
common occurrences, *vast* graveyard of death, 
even for most of the 20th century..
could rats be picking up the parasite from dead human soldiers???

and think.. human soldiers are almost *uniformly*male*.
so... maybe the parasite is subtly altering human *male* 
behavior to twist them towards soldier-like mentality, 
i.e. battlefield-rat-fodder???

crazy??? maybe. (which--me, or human history??)
flegr's psychological results show that
males become *less*moral* and *more*expedient*. the studies
show decreased IQ among toxoplasma positive humans in

so-- human males nudged into dumb, violent killing machines??? in
addition to rodent kamakazes, could it be helping make 
*human* kamakazes as well? with possibly
up to *half* the world population affected, what would
be the cumulative effect on human culture if this parasite did *not*
inhabit our brains??? would it be different?? is it an
explanation for some of our collective, suicidal tendencies as
a race???

one straightforward way to study the question of 
t.gondii behavior manipulation on mass human behavior: look at 
incidence of infection among different occupational segments
(including the military!!) this study would probably furnish
useful information regardless of the results (such as higher-risk
occupations etc).


I've proposed some radical ideas above that no respectable
scientist would, which many will probably laugh at or
even attack if they even hear about them. 
but from what I can tell, these suggestions, some bordering
on wild, cannot be ruled out by existing knowledge of t.gondii, 
which is very minimal relative to its nature particularly
in humans. 

due to the miracle of cyberspace, I can post these musings
here for you instantaneously, almost simultaneously as
I write them. take them for what they are worth.

my basic suggestion is that humans may not be an incidental
or "dead end" host for t.gondii, but an important intermediary host. that
is a rather bizarre suggestion by current conventional 
wisdom, but as far as I know not ruled out by existing knowledge.

once the realization that humans may not be an incidental
or "dead end" host is taken seriously, this leads to other
ideas, implications, ramifications.  purposeful behavior manipulation
by the parasite is not so outlandish if any new human-exiting 
transmission pathways are discovered.

I've included a few suggestions, ranging into the admittedly
bizarre, along the lines of possible meanings of the 
human behavior manipulations. maybe they are incorrect. or maybe
t.gondii is doing something even more outlandish than even I can
conceive of!!

I can see the scientific establishment's gears 
are slowly turning on all this, but on the other hand,
only a few scientists in the world are studying t.gondii and
even fewer its full implications in humans.  I do believe we 
will have answers to questions raised here.. I am posting this in 
the hope they will come "sooner" rather than "later"!!!


carl zimmers book on parasitology, (c) 2000.. see especially
the chapter on parasite-host behavior manipulation. very
little on t.gondii in this book, all filed under the assumption 
it is innocuous in humans.


this news article on zimmers site mentions flegr's 
and websters research into t.gondii, the "alter host behavior"


bbc news article focuses on websters rat alteration findings


lingua franca article linking up t.gondii to schizophrenia


huge slide show on t.gondii from conference in 2000, 
partly focused on the schizophrenia angle but very
interdisciplinary.. warning, hundreds of images, you
need a fast internet connection for this


jaroslav flegr, papers on effect of t.gondii on human behavior


joanne webster, expert on t.gondii & effect on rat psychology.
webster has a nice survey article on t.gondii that I have
an electronic version of, published in 2001.


more on rodent kamakazes, manuel berdoy quoted 
that humans are a "dead end" for the parasite


section on parasites altering their hosts appearance
and/or behavior, from a radio show on parasites. 
webster, berdoy, smith comment on toxoplasma gondii.


example of the scientific paradigm shift currently going on
over parasites, i.e. idea that many human ills stem
from them.. t.gondii mentioned in passing


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