The Influence of Latent
Toxoplasmosis on Human Personality
Jaroslav Flegr, Department of Parasitology, Charles University,
Prague, Czech Republic
The
most frequent form of human toxoplasmosis is an acquired latent toxoplasmosis.
Its prevalence varies in different countries usually between 20 to 60%.
Latent toxoplasmosis is usually considered to be an asymptomatic
parasitosis. Most of infected
subjects never realize that they have been infected with T. gondii and
harbor dormant stages of the parasite (cysts I nervous and muscle tissues) for
the rest of their life. T.
gondii is known to specifically influence the behavior of its animal
intermediate hosts. Presently, the
behavioral effects of latent toxoplasmosis is mostly considered to be an
evolutionary adaptation of the parasite aimed to increase the probability of
transmission of the infection from an intermediate host (usually rodent) to a
definitive host (cat) by predation. Experimental
data show that the mechanism of manipulation involves the induction of changes
of level of some neurotransmitter (possibly dopamine) in the brain of infected
hosts. In human host, such changes
in the neurotransmitter levels could be expected to result in changes in
personality profile. Therefore,
since early 90s, we have been looking for changes in personality profiles of
subjects with latent toxoplasmosis. The
aim of first group of studies (10 independent data sets) was to find out whether
the personality profile of subjects with latent toxoplasmosis differ from those
of Toxoplasmo-negative controls. In
these double-blind studies the subjects completed a personality questionnaire
and then were serologically examined for latent toxoplasmosis.
Aim of the second group of studies (3 independent data sets) was to find
out whether the shift in personality profile increases or decreases with the
duration of infection. Two of these
studies involved subjects who were treated for acquired acute toxoplasmosis in
different Prague hospitals during past 14 years. The duration of infection was not known for subjects involved
in the third study and was only indirectly estimated on the basis of level of
specific antibodies. The possible
influence of age of infected subjects and other potential confounding factors
were statistically filtered out and the results were corrected for multiple
tests. The results of particular
studies are shown in the Table. Generally,
statistically significant influence of latent toxoplasmosis on human personality
was observed in all studies. The direction of personality shifts was more or less similar
in all studies. However, it
remarkably differed between men and women.
The personality of infected men was mostly shifted towards low superego
strength and high protension
(factors G and L of Cattell’s 16PF), i.e. the men had tendency to disregard
rules, were more expedient, suspecting, jealous, dogmatic.
They had also lover Self-directiveness a Cooperativeness (measured with
Cloninger TCI test). Infected women
had higher affectothymia and superego strength (A and G), which means they were
more warm-hearted, outgoing, easygoing and more conscientious, persistent,
moralistic and staid. Both men and
women had higher guilt proneness (O), which means that they were more
apprehensive, self-reproaching, insecure. The
intensity of personality factor changes increased with the duration of
toxoplasmosis suggesting that slow commutative effects of latent toxoplasmosis,
rather than one-step and transient effect of acute toxoplasmosis is responsible
for the observed changes. Our
results suggest that the latent toxoplasmosis might be in fact a very serious
and highly underappreciated public health problem in most of developed
countries.
|
Set
|
Test
|
N
|
Toxo
preval.
|
Changes in personality profiles
|
|
Biologists
Men1,2
|
Cattell 16 PF
|
243
|
28%
|
Decr. G (superego strength) p=0.05, incr. L (protension) p=0.015,
Incr. O (guilt proneness) p=0.041
|
|
Biologist
Women1,2
|
Cattell 16 PF
|
200
|
22%
|
Incr. A (affectothymia) p=0.004
|
|
Patients men2
|
Cattell 16 PF
|
164
|
100%
|
Decr. G (superego strength )p=0.017, decr. B (intelligence) p-0.062
|
|
Patients women3
|
Cattell 16 PF
|
243
|
100%
|
Incr. G (superego strength) p=0.010, incr. Q3 (strength of self sentiment) p=0.062
|
|
Mothers4
|
Cattell 16 PF
|
191
|
28%
|
Incr. B (intelligence) p=0.03, incr. O (guilt proneness) p=0.02
|
|
Mothers
Toxo-posit3
|
Cattell 16 PF
|
191
|
28%
|
Incr. A (affectothymia) p=0.003, incr. G (superego strength) p-0.013
|
|
Blood donors
Men
|
Cattell 16 PF
|
31
|
61%
|
Decr. G (superego strength ) p=0.043, decr. N (shrewdness)
|
|
Blood donors
Women
|
Cattell 16 PF
|
24
|
49%
|
Incr. A (affectothymia) p=0.013, incr. N (shrewdness)
|
|
Conscripts
|
Cloninger TCI
|
252
|
25%
|
No significant change
|
|
Conscripts
(drivers)
|
WMT
|
128
|
27%
|
Decr. IQ p=0.009
|
Table
1. The influence of latent toxoplasmosis on human personality.
A list of all experimental sets studied between 1992-2000.
1)
Flegr J., Zitková Š., Kodym P., Frynta D.; 1996: Induction of changes in human
behaviour by the parasitic protozoan Toxoplasma
gondii.
Parasitology, 113, p. 49 – 54. 2) Flegr, J., Hrdá, Š. a Havlíček,
J. Rozdíly v osobnostním profilu biologů nakažených a nenakažených
T. gondii
Remedia – Klinická Mikrobiologie, 3: 268-273. 3) Flegr,
J. Kodym, P. and Tolarová V. Correlation of duration of latent Toxoplasma gondii infection with personality changes in women.
Biological Psychology 53: 57-68. 4) Flegr
J., Havlíček J. 1999 Changes in the personality profile of young women
with latent toxoplasmosis. Folia
Parasitologica, 46: 22-28.
OF SLIDES 23-25