Probable neuroimmunological link between Toxoplasma and cytomegalovirus infections and personality changes in the human host
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Novotná, M., Hanusova, J, Klose J., Preiss, M., Havlicek, J., Roubalová, K., Flegr, J.
BMC Infectious Diseases 2005; 5: 54
Novotná, M., Hanusova, J, Klose J., Preiss, M., Havlicek, J., Roubalová, K., Flegr, J.
BMC Infectious Diseases 2005; 5: 54
Click for abstract
Background:
Recently, a negative
association between
Toxoplasma
-infection and novelty s
eeking was reported. The
authors suggested that changes of pers
onality trait were caused by manipula
tion activity of the parasite, aimed at
increasing the probability of tr
ansmission of the parasite from an intermedia
te to a definitive host
. They also suggested
that low novelty seeking indicated an in
creased level of the neurot
ransmitter dopamine in the
brain of infected subjects,
a phenomenon already observ
ed in experimentally infected ro
dents. However, the changes in
personality can also be just
a byproduct of any neurotropic infection
. Moreover, the association between a pe
rsonality trait and
the toxoplasmosis
can even be caused by an independent
correlation of both the probability of
Toxoplasma
-infection and the personality
trait with the third factor, namely with th
e size of living place of a subject. To
test these two alternative hypotheses, we
studied the influence of another neurotropic pathogen, the cyto
megalovirus, on the personali
ty of infected subjects, and
reanalyzed the original data after the
effect of the potential confounder, the si
ze of living plac
e, was controlled.
Methods:
In the case-control study, 533 conscr
ipts were tested for to
xoplasmosis and presence
of anti-cytomegalovirus
antibodies and their novelty se
eking was examined with Cloninger's TCI questionnaire. Possible association between the
two infections and TCI dimensions was analyzed.
Results:
The decrease of novelty seeking is as
sociated also with cytomegalovirus infe
ction. After the size of living place
was controlled, the effect of to
xoplasmosis on novelty seeking increased. Si
gnificant difference in novelty seeking was
observed only in the largest city, Prague.
Conclusion:
Toxoplasma
and cytomegalovirus probably induce a decrease
of novelty seeking.
As the cytomegalovirus
spreads in population by direct contact (not by predation as with
Toxoplasma
), the observed changes are the byproduct
of brain infections rather than
the result of manipulation activity of a parasite
. Four independent line
s of indirect evidence,
namely direct measurement of neurotransmi
tter concentration in mice, the nature of
behavioral changes in rodents, the
nature of personality changes in humans, and the observed
association between schizophren
ia and toxoplasmosis, suggest
that the changes of dopamine concentration in brain coul
d play a role in behavioral changes of infected hosts.