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Disciplines such as business and economics often rely on the assumption of rationality when explaining complex human behaviours. However, growing evidence suggests that behaviour may concurrently be influenced by infectious microorganisms. The protozoan Toxoplasma gondii infects an estimated 2 billion people worldwide and has been linked to behavioural alterations in humans and other vertebrates. Here we integrate primary data from college students and business professionals with national-level information on cultural attitudes towards business to test the hypothesis that T. gondii infection influences individual- as well as societal-scale entrepreneurship activities. Using a saliva-based assay, we found that students (n = 1495) who tested IgG positive for T. gondii exposure were 1.4× more likely to major in business and 1.7× more likely to have an emphasis in 'management and entrepreneurship' over other business-related emphases. Among professionals attending entrepreneurship events, T. gondii-positive individuals were 1.8× more likely to have started their own business compared with other attendees (n = 197). Finally, after synthesizing and combining country-level databases on T. gondii infection from the past 25 years with the Global Entrepreneurship Monitor of entrepreneurial activity, we found that infection prevalence was a consistent, positive predictor of entrepreneurial activity and intentions at the national scale, regardless of whether previously identified economic covariates were included. Nations with higher infection also had a lower fraction of respondents citing 'fear of failure' in inhibiting new business ventures. While correlational, these results highlight the linkage between parasitic infection and complex human behaviours, including those relevant to business, entrepreneurship and economic productivity.
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Cite this article: Johnson SK, Fitza MA,
Lerner DA, Calhoun DM, Beldon MA, Chan ET,
Johnson PTJ. 2018 Risky business: linking
Toxoplasma gondii infection and
entrepreneurship behaviours across individuals
and countries. Proc. R. Soc. B 285: 20180822.
Received: 13 April 2018
Accepted: 28 June 2018
Subject Category:
Subject Areas:
health and disease and epidemiology,
environmental science, behaviour
Toxoplasma gondii, entrepreneurship, parasite
manipulation, disease ecology, human
behaviour, emerging infectious disease
Author for correspondence:
Stefanie K. Johnson
Electronic supplementary material is available
online at
Risky business: linking Toxoplasma gondii
infection and entrepreneurship behaviours
across individuals and countries
Stefanie K. Johnson1, Markus A. Fitza3, Daniel A. Lerner4, Dana M. Calhoun2,
Marissa A. Beldon1, Elsa T. Chan5and Pieter T. J. Johnson2
Leeds School of Business, and
Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
Frankfurt School of Finance and Management, Frankfurt, Germany and Nord University Business School, Bodø,
Deusto Business School, University of Deusto, Bilbao, Spain
Department of Management, College of Business, City University of Hong Kong, Kowloon Tong, Hong Kong
PTJJ, 0000-0002-7997-5390
Disciplines such as business and economics often rely on the assumption of
rationality when explaining complex human behaviours. However, growing
evidence suggests that behaviour may concurrently be influenced by
infectious microorganisms. The protozoan Toxoplasma gondii infects an esti-
mated 2 billion people worldwide and has been linked to behavioural
alterations in humans and other vertebrates. Here we integrate primary
data from college students and business professionals with national-level
information on cultural attitudes towards business to test the hypothesis
that T. gondii infection influences individual- as well as societal-scale entre-
preneurship activities. Using a saliva-based assay, we found that students
(n¼1495) who tested IgG positive for T. gondii exposure were 1.4more
likely to major in business and 1.7more likely to have an emphasis in
‘management and entrepreneurship’ over other business-related emphases.
Among professionals attending entrepreneurship events, T. gondii-positive
individuals were 1.8more likely to have started their own business com-
pared with other attendees (n¼197). Finally, after synthesizing and
combining country-level databases on T. gondii infection from the past 25
years with the Global Entrepreneurship Monitor of entrepreneurial activity,
we found that infection prevalence was a consistent, positive predictor of
entrepreneurial activity and intentions at the national scale, regardless of
whether previously identified economic covariates were included. Nations
with higher infection also had a lower fraction of respondents citing ‘fear
of failure’ in inhibiting new business ventures. While correlational, these
results highlight the linkage between parasitic infection and complex
human behaviours, including those relevant to business, entrepreneurship
and economic productivity.
Significance statement
Toxoplasma gondii is a protozoan parasite estimated to infect over 2 billion people
worldwide. While rarely associated with acute pathology, latent infections have
increasingly been linked to subclinical outcomes such as caraccidents, neuroticism
and suicides through their potential influence on personality and risk-taking beha-
viours. Whether such effects extend to business-related behaviours among
individuals and across populations remains conjectural. By combining data
from university students, business professionals and global databases, we high-
light the consistent and positive link between T. gondii exposure and
entrepreneurial behaviour at both local and international scales. These findings
emphasize the ‘hidden’ role of parasites as potential drivers of complex human
behaviour and economic outcomes.
&2018 The Author(s) Published by the Royal Society. All rights reserved.
on August 7, 2018 from
1. Introduction
When explaining complex human behaviours, disciplines
such as business and economics often rely heavily on the
assumption of rationality—that individuals consider the
costs, benefits, risks and probabilities of a decision and then
behave in a way to maximize their own outcomes [1].
Although research in behavioural economics has increasingly
acknowledged and explored the factors that contribute to
deviations from rationality, these often focus on standard
cognitive biases [2,3]. Comparatively little research has
addressed the influence of biological factors generally, and
of infectious microorganisms in particular, on the cornerstone
assumption of rational decision-making [4,5] and overall
patterns of impulsivity, including risk-taking behaviour
[6]. Emerging research in the biological sciences highlights
the importance of transmissible agents—ranging from
viruses to worms—in collectively shaping host immunity,
mental health and even mate attraction [79]. The goal of
this study was to investigate how infection by a globally
distributed parasite—through its potential influence on
individual human behaviour—is associated with local to
large-scale cultural and business-related outcomes, specifically
The protozoan parasite Toxoplasma gondii infects an esti-
mated 2 billion people worldwide [10,11]. Although over
100 species of vertebrates can become infected with
T. gondii, the parasite reproduces sexually only within wild
and domestic cats [11,12]. Thus, adaptations by the parasite
that increase predation risk by cats should be selectively
favoured from an evolutionary standpoint [9,12,13]. Exper-
imental studies from non-human systems indicate that
T. gondii infection is associated with increased risk-taking
behaviours, including an attraction towards cat urine, greater
exploration of novel areas in mazes and reduced avoidance of
open spaces [14– 16]. Similar forms of both subtle and dra-
matic behavioural modification have been hypothesized in
humans [17]: T. gondii hasbeenlinkedtooutcomessuch
as a greater risk of car accidents, mental illness, neuroticism,
drug abuse and suicide [13,1821]. The infection-associated
changes in the brain that precipitate increased impulsivity
are complex and not fully understood [22] although changes
in the production, metabolism, or synthesis of both hormones
(e.g. testosterone) and neurotransmitters (e.g. serotonin,
dopamine and norepinephrine) have been explored [23].
Increases in testosterone, for instance, which have been
linked to T. gondii infection [24], can enhance risk-taking
behaviour, aggression and impulsivity in humans [17,25].
The psycho-behavioural linkages between T. gondii and
human behaviour raise an intriguing question: to what
extent do the effects of infection on behaviour affect indi-
vidual- and population-level patterns in the success of
new business ventures. Infection and the associated hor-
monal and neurological changes have the potential to
amplify impulsivity, sensation-seeking, and risk-taking
behaviours, as well as an individual’s focus on ego, ambi-
tion, material possessions and self-achievement (at least in
men)—characteristics often associated with entrepreneurial
activity [17,20,26]. Studies of entrepreneurship at both the indi-
vidual and societal levels have repeatedly emphasized the
importance of specific traits, such as risk tolerance and lower
fear of failure in determining entrepreneurship outcomes
[27]. Alongside its effects on individuals, T. gondii infection
has also been hypothesized to affect national-level cultural
and economic outcomes [13,28]. There is strong global vari-
ation in T. gondii prevalence—from 9% in Norway to 60%
in Brazil—which correlates positively with aggregate neur-
oticism [13] and negatively with institutional quality and
economic performance by country [28].
Here we examined how infection by Toxoplasma gondii
underlies heterogeneity in entrepreneurship attitudes and
activity, first among individuals in university and pro-
fessional populations, and then extending these results to
global patterns in entrepreneurship. Specifically, we evaluate
whether infection—through its hypothesized link to risk-
taking behaviour—reduces the ‘fear of failure’ that often
limits the entrepreneurial tendencies of individuals, thereby
shaping larger-scale entrepreneurship activity and culture.
Using a saliva-based assay of IgG antibodies, we tested the
degree to which infection status predicted university
students’ tendency to major in business- and entrepreneurship-
related disciplines, and professionals’ success at starting
their own business. To assess whether such individual-level
patterns translated into national-scale outcomes, we coupled
country-level databases on T. gondii infection from the past
25 years with results from the Global Entrepreneurship
Monitor (GEM) of entrepreneurial activity, both with and
without relevant covariates. By identifying how T. gondii
infection at multiple scales predicts entrepreneurial activity
and intent, these findings highlight the potential role of infec-
tious organisms in shaping patterns of entrepreneurship
behaviour and, by extension, the global economy.
2. Material and methods
(a) Study 1: infection patterns in university students
Data on major field of study and T. gondii antibody prevalence
were collected from 1495 undergraduate students in general
biology and business classes at a large US university. Students
apply for admission to one of the colleges on campus which
include Arts and Sciences, Business, and Engineering. Once
admitted to a college, students select a major emphasis of
study within that college. Within Business, students can major
in finance, accounting, marketing or management and entrepre-
neurship. Within Arts and Sciences, students can major in
biology, psychology, physics, chemistry, among others.
While past research has often used serum samples, recent
advances have facilitated the use of saliva as a less-invasive
alternative to assess T. gondii infection [29]. Here, we used and
validated an indirect competition immunoenzymatic (ELISA)
saliva-based assay to test for T. gondii IgG antibodies. Subjects
chewed on a sponge (SalivettesTM) for 120 s, after which each
sample was run in duplicate alongside five manufacturer IgG
seropositive controls (provided by Accurun
135), three saliva-
positive controls (from known T. gondii-positive subjects), five
saliva negative controls (from known T. gondii-negative subjects)
and five blanks (samples with no saliva to baseline-correct the
optical density (OD) per plate). Positive and negative saliva
controls were tested using a quantitative immunoenzymatic
assay for Toxoplasma IgG (Immuno-Biological Laboratory (IBL);
Hamburg, Germany) and verified through a secondary reference
laboratory (Quest DiagnosticsTM; San Juan, California) using a
sandwich competitive ELISA. Subject samples were considered
positive if the observed OD values were at least two standard
deviations greater than the average negative control value from
the corresponding plate. We validated this classification
approach by calculating method sensitivity and specificity, as Proc. R. Soc. B 285: 20180822
on August 7, 2018 from
well as comparisons with receiver operator characteristic curves
based on threshold values (see electronic supplementary
material, SI [30]). Ambiguous subjects in which the duplicate
samples gave conflicting results were re-run. Results from anti-
body testing were linked to each student’s indicated major, for
which we performed comparisons both between Business-related
majors and non-Business majors as well as within business-
related majors by comparing the ‘management and entrepre-
neurship’ emphasis with all other business emphases
(accounting, finance, marketing) and specifically to accounting,
which is considered the most risk-avoidant emphasis consider-
ing its high placement rate ( percent of students who receive job
offers in their selected career field). Our rationale was that
Business majors would be more interested in entrepreneurship
than other majors and within the Business major, students who
study ‘management and entrepreneurship’ would be more
inclined towards entrepreneurship than other emphases, such
as accounting. The total sample size of subjects with useable
information on infection status and field of study was 1293
(electronic supplementary material, table S1).
(b) Study 2: infection patterns in business professionals
To understand patterns of infection among professional entre-
preneurs, we collected data from 197 individuals attending
entrepreneurship events. All individuals at the locations were
invited to participate by providing a saliva sample, as outlined
above. Participants were given a colour-coded vial based on
their sex and whether or not they had ever started their own
company, and samples were processed as described above.
For both Study 1 and Study 2, we used generalized linear
models with a binomially distributed response and the comp-
lementary loglog link function to evaluate the influence of
T. gondii infection status (antibody-negative versus antibody-
positive) on major field of study (Business major versus
non-Business majors, and ‘management and entrepreneurship’
emphasis versus other emphases within the Business discipline),
and entrepreneurial tendencies (self-identified as having suc-
cessfully started a business). Subject sex (male or female)
and a sex-by-infection interaction were also included in all
analyses; for Study 1, we also included a variable for grade
point average (GPA) to account for grade-based admission
requirements in different colleges (missing values were replaced
with the mean GPA).
(c) Study 3: global patterns of toxoplasmosis
and entrepreneurship
Existing databases of T. go ndii infection prevalence at the
country level (the proportion of samples that tested positive
for T. gondii within a country-specific survey) were compiled
using published data and reviews (see electronic supplemen-
tary material ). The data were restricted to studies conducted
after 1990. When more than one T. gond ii prevalence study
was available for a given country, we used the average (elec-
tronic supplementary material, table S2). Because countries
vary in the average age at which women get pregnant and thus
the number of years of potential exposure to T. gondii, we used
prevalence estimates standardized to an age of 22 years following
Lafferty [13] (also see [28]).
To assess entrepreneurship, we used the GEM of entrepre-
neurial activity. The GEM database is the result of a
worldwide consortium of universities (www.gemconsortium.
org), with data derived from national surveys of entrepreneurial
climate, activities and attitudes. We used GEM data collected
from 2000 to 2010, using the most recent data for counties
that were surveyed more than once during the study period.
Our three dependent variables were the proportion of people
in a country with entrepreneurial intentions (Futsupno), the pro-
portion engaged in entrepreneurial activity (teayy), and the
proportion inhibited from starting a business by their fear of
failure (Frfailop) (see electronic supplementary material for
additional variable descriptions). Because all dependent vari-
ables have values that range from zero to one, we used
generalized linear models with a binomial distribution, follow-
ing McDowell & Cox [31]. The control variables used in the
standard GEM model [32] are described in the electronic sup-
plementary material, although we ran analyses with and
without these variables to ensure that findings were robust
(see electronic supplementary material ). Overlaying the GEM
and T. gondii data sources yielded a database for 42 countries
(see electronic supplementary material, table S2). We hypoth-
esized that T. gondii prevalence would associate positively
with the proportion of people in a given country that intend
to start a new business or are currently engaged in entrepre-
neurial activities, and negatively with the proportion of
people inhibited from starting a business by fear of failure.
We did not include interactions between infection prevalence
and GEM covariates given the lack of apriorihypotheses and
the desire to avoid overfitting the models.
3. Results
(a) Study 1: infection patterns in university students
Based on an analysis of T. go ndii IgG prevalence from 1495
university students, 22% tested positive. There were 968
confirmed negative cases and 199 samples classified as
‘ambiguous’ even after retesting, which were removed
from further analysis, leaving 1293 included cases. Using
the 2SD classification method, 195 of 201 known positive
samples (97% sensitivity) and 186 of 186 known negative
samples (100% specificity) were classified correctly. Infec-
tion status was a significant, positive predictor of students’
tendency to major in business-related fields (B¼0.33,
s.e. ¼0.10, p,0.005), while controlling for sex and GPA
(although results were comparable with these covariates
removed). Among Business students, 146 of 475 individuals
(31%) tested positive for T. gondii IgG, whereas 179 of 818
(22%) of non-Business majors were antibody-positive. The
odds of being a Business major were 1.4greater for anti-
body-positive students [95% CI ¼(1.1, 1.7)] relative to
those testing negative (figure 1). Female students were
also less likely to be Business majors (B¼20.53, s.e. ¼
0.09, p,0.01), whereas GPA had no effect. Within the
Business major specifically, students with evidence of
T. gondii exposure were 1.7more likely to have an estab-
lished emphasis in ‘management and entrepreneurship’
[95% CI ¼(1.0, 2.8)] relative to other Business subdisciplines
(B¼0.52, s.e. ¼0.27, p¼0.054 (figure 1).Twenty-four of the
57 (42%) ‘management and entrepreneurship’ majors tested
positive for T. gondii compared with 63 of the 216 (29%) stu-
dents majoring in accounting, finance or marketing. GPA
also associated negatively with the management/entrepre-
neurship emphasis (B¼20.68, s.e. ¼0.29, p,0.05), while
sex showed no relationship. This contrast was even more
pronounced in comparing the influence of infection status
on the likelihood of a concentration in management/entre-
preneurship versus accounting specifically (B¼0.63, s.e. ¼
0.30, p,0.05). There were no significant interactions
between sex and infection status for any of the response
variables, and statistics are reported from models without
this term. Proc. R. Soc. B 285: 20180822
on August 7, 2018 from
(b) Study 2: infection patterns in entrepreneurs
Consistent with the undergraduate data, T. gondii antibody
status was a positive predictor of entrepreneurship among
professionals attending entrepreneurship events (B¼0.59,
s.e. ¼0.29, p,0.05). The odds of having successfully started
a business were 1.8greater among antibody-positive indi-
viduals [95% CI ¼(1.0, 3.2)] compared with those who
tested negative (4 of 73 versus 17 out of 124) (figure 1).
(c) Study 3: global patterns of toxoplasmosis
and entrepreneurship
Extending the analysis of infection and entrepreneurship to
the global extent, we detected a positive association between
T. gondii infection prevalence among 42 countries and both
the proportion of people intending to start their own business
(B¼2.49, s.e. ¼0.30, p,0.001; figure 2a) and the proportion
currently engaged in entrepreneurial activity (B¼1.39, s.e. ¼
0.38, p,0.01; figure 2b) (see electronic supplementary
material, tables S3 and S4). Correspondingly, T. gondii infec-
tion negatively predicted the proportion of a country’s
population inhibited from starting a business by their fear
of failure (B¼20.71, s.e. ¼0.24, p,0.01; figure 2c).
Among all countries, the average age-adjusted T. gondii preva-
lence was 0.34 (figure 2). The heat map shows countries with
greater levels of entrepreneurship (darker blue countries) have
higher T. gondii prevalence (darker red dots). These results
were robust to alternative forms of analysis and the inclusion
of standard control covariates (see electronic supplementary
material). Thus, the coefficient estimates for T. gondii prevalence
on each entrepreneurship response variable were broadly
consistent regardless of whether covariates from the GEM
model were included (figure 3).
4. Discussion
Research in business and economics have traditionally
emphasized the importance of rationality in explaining com-
plex human behaviours [33], yet the additional influence of
biological factors generally and of infectious microorganisms
in particular on this cornerstone assumption have rarely been
examined [4,5]. By integrating research on entrepreneurship,
epidemiology, and behavioural outcomes, this study high-
lights linkages between infection by the globally distributed
parasite T. gondii and entrepreneurship behaviours among
individuals and across countries. Based on a saliva-based anti-
body assay applied to 1495 students from a large US
university, infection increased the odds of majoring in a
Business-related discipline by 1.4relative to uninfected stu-
dents. Within Business majors specifically, T. gond ii-positive
individuals were 1.7more likely to have self-selected into
the ‘management and entrepreneurship’ emphasis relative to
other emphases (accounting, finance and marketing). Extend-
ing this analysis to members of the professional community,
Study 2 indicated that individuals previously exposed to
T. gondii were 1.8more likely to have started a business rela-
tive to attendees who tested negative. By combining global
information on T. gondii prevalence and entrepreneurship
behaviours among 42 countries, our analyses further indicated
that populations with higher T. gondii prevalence had greater
intentions to start a business and higher levels of active entrepre-
neurship behaviours. These countries also had a lower fraction
of respondents who cited ‘fear of failure’ as a factor preventing
them from initiating a business-related enterprise.
Mechanistically, the observed linkages between T. gondii
infection and entrepreneurship among students, professionals,
and nations have several potential interpretations. Given the
correlational nature of the study, observed patterns may not
be causal; for example, higher risk-takers could be more
likely to be both entrepreneurial and exposed to T. gondii
(e.g. by consuming raw/undercooked meat), thereby driving
the correlation. Although causality cannot be inferred, the
cross-sectional field design represents a strength of the current
study in comparison to case-control methodology, for which
the selection of controls is non-random and influenced by
self-selection biases [34]. By surveying a population of stu-
dents, rather than known-positives and matched controls,
we minimized the risk of selection bias in that regard. None-
theless, whether an individual becomes an entrepreneur
depends on many factors, such as access to resources and insti-
tutional support (e.g. [35]). Thus, the relationship between
T. gondii and a complex phenomenon such as entrepreneurial
activity is expected to be multifactorial and probably influ-
enced by additional, unmeasured variables that affect both
parasite exposure and entrepreneurship at the individual
or national scale. At the global extent, for instance, patterns
related to climate, ecology, soil exposure or biogeographic
history probably affect the distribution of parasite exposure
directly or through their influence on food preferences (includ-
ing the consumption of raw or undercooked meat) and human
culture [11,36– 38].
The more intriguing possibility is that infection directly
or indirectly enhances entrepreneurial tendencies within
individuals and specific cultures. Experimental evidence
business major management entrepreneur
effect of Toxoplasma infection
(odds ratio)
response variable
Figure 1. Relation between T. gondii infection and entrepreneurial out-
comes among university students and business professionals. Presented
for each analysis is the odds ratio (+0.95% CI) for infection on: the like-
lihood a sampled student was a Business major relative to an Arts and
Sciences major (n¼1293), whether Business majors self-selected into
the management and entrepreneurship focus relative to other business-
related subdisciplines (n¼273), and, among professionals in the commu-
nity, the likelihood an individual successfully started a business (n¼197).
For the analyses of student majors, GPA, and sex were included as cov-
ariates; for the professionals, sex was included as a covariate. (Online
versionincolour.) Proc. R. Soc. B 285: 20180822
on August 7, 2018 from
from rodent models is often cited to support the causal link
between infection and altered host behaviour [39 41]. Infec-
tion is associated with increased risk-taking behaviours,
potentially due to hormonal or neurological changes result-
ing from encysted T. gondii in the brain [42]. Samojlowicz
et al. [21] found a significant, positive relationship between
T. gondii infection and risky behaviours, including substance
overdose, suicide, not wearing a helmet and alcohol con-
sumption. Correspondingly, entrepreneurs tend to score
higher in risk-taking (and lower in risk-avoidance), need
for achievement and overconfidence [43]. The hypothesized
increase in impulsivity and risk-taking associated with infec-
tion could, therefore, encourage individuals to engage in
entrepreneurial activity [17,21]. Although this study did not
include specific measures of personality, individual infection
status among university students and business professionals
was a positive predictor of interest in entrepreneurship or
entrepreneurial success. Among nations, higher levels of
infection were associated with a reduction in the popu-
lation’s ‘fear of failure’ in initiating a business venture,
consistent with higher overall levels of entrepreneurial
intent or activity ( figure 2). This relationship persisted even
when controlling for previously identified covariates from
the GEM database, such as financial need, institutional or
governmental support, educational opportunities and social
norms (electronic supplementary material; figure 3). Previous
analysis of the GEM database shows that factors like social
norms and education are among the most highly related
factors to entrepreneurship [28].
Previous, large-scale analyses of T. gondii prevalence
among countries have shown that infection is linked to neur-
oticism, uncertainty avoidance, and economic prosperity
[13,28]. For example, Lafferty [13] found that infection preva-
lence among 27 Western nations correlated negatively with
uncertainty avoidance, although this relationship was not sig-
nificant when eastern and Western cultures were combined.
Maseland [28] reported a negative link between T. gondii
infection and the economic outcomes of associated nations,
including the countries used here. Arguably, such findings
might lead to the opposite expectation of the patterns
observed in the current study: that infection prevalence
would associate with more risk-averse individuals and
0 0.1 0.2
entrepreneurial intent (%)
entrepreneurial activity (%)
fear of failure (%)
0.3 0.4 0.5 0.6 0.7 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.1
Toxoplasma gondii
revalence Toxoplasma gondii
revalenceToxoplasma gondii
0.2 0.3 0.4 0.5 0.6 0.7
entrepreneurial intent (%)
0.70 62.60
8.61 60.37
T. gondii (prevalence)
Figure 2. Heat map illustrating the geographical distribution of T. gondi i infection and the proportion of a country’s population with entrepreneurial intentions.
(a) The colour of the country reflects the fraction of surveyed respondents with intentions to start their own business (from light blue to dark blue), while the
colour of the superimposed circle reflects the magnitude of infection (from light yellow to dark red). Only countries with surveys of T. gond ii and entrepreneurial
activity since 1990 are included. Infection data from Maseland [28] and sources therein while entrepreneurship information was derived from the GEM database.
The relationship between T. gondii infection prevalence and the three specific variables related to entrepreneurial attitudes and activity are presented in the
scatterplots. Response variables from the GEM database included the proportion of a country’s population (b) with entrepreneurial intentions (intend to start a
business within three years), (c) that are currently engaged in entrepreneurial activity, or (d) that cited ‘fear of failure’ as a factor inhibiting them from starting a
business. All relationships were significant based on generalized linear models with a binomial distribution (see electronic supplementary material, tables S2, S3
and S4). (Online version in colour.) Proc. R. Soc. B 285: 20180822
on August 7, 2018 from
reduced entrepreneurial innovation. However, extensive evi-
dence linking infection to reduced fear makes a compelling
case for a positive linkage with entrepreneurship [6,17]. The
complex associations between T. gondii and behavioural pat-
terns among countries may also depend on geographical
variation in the strain or lineage of the parasite and the rela-
tive frequency of alternative exposure pathways (e.g. through
cat exposure versus undercooked meat [10,11,44,45]).
The current findings raise questions regarding the impli-
cations of infection for individual entrepreneurs, aggregate
societies and the associated economic outcomes. Entrepre-
neurship has been characterized as a high-risk, high-reward
endeavour, for which the risk often comes at the cost of econ-
omic stability for an individual [46,47]. Because the risk
almost always outweighs the reward, such that the prob-
ability of high reward is generally low, economic models
indicate that entrepreneurship is rarely a rational decision
for the individual [47]. Any factor that increases the tendency
of an individual to engage in entrepreneurial activities
would, therefore, amplify the probability of negative financial
outcomes, except among the very poor for whom opportu-
nity costs are lowest [46,47]. Among individuals who have
already elected to become entrepreneurs, the potential effects
of T. gondii on individual-based outcomes will depend on
whether infection leads to poor decisions or simply limits
the ‘fear of failure’ that would have otherwise impeded an
entrepreneur from engaging in a successful endeavour. As
we found in the global patterns study, reduced fear of failure
could explain the relationship between T. gondii infection
and entrepreneurship, although assessing this possibility
will require comparisons of entrepreneurs as a function of
T. gondii exposure history. By contrast with the consequences
for individuals, there are clear benefits of increased entrepre-
neurship at the societal scale in terms of job growth,
economic development, and innovation [48 51]; even if
associated with greater infection by T. gondii, the enhanced
innovation emerging from greater entrepreneurial engage-
ment within the population would likely be positive.
While increased disease risk is often associated with
higher collectivism and greater xenophobia [52], its impli-
cations for transformational creativity and the resultant
economic rewards remain relatively unexplored—particularly
for pathogens that may cause individuals to deviate from
rational economic theory.
In sum, emerging research in the biological sciences has
increasingly emphasized the importance of transmissible
agents—ranging from viruses to worms—in collectively
shaping host immunity, mental health and even mate attrac-
tion [79]. Such findings suggest that infections—through
their influence on individual behaviour—further have the
potential to affect large-scale cultural and business-related
outcomes. Here we hypothesized a connection between the
general effects of T. gondii in individuals with extant entrepre-
neurship research, highlighting the alignment between
psychological factors known to favour entrepreneurial inten-
tion and infection. What drives differences in entrepreneurial
activity rates remains an important question (e.g. [53,54]), for
which this study offers insight into the potential role of
infection at the individual as well as country level (e.g. [55]).
Ethics. The data collection from humans was approved by the insti-
tutional review board at the University of Colorado (IRB Protocol
no. 15-0004) and an informed consent form was given to all
Data accessibility. The data and metadata associated with this article
are available at Dryad Digital Repository (doi:10.5061/dryad.
gd19rr3) [56].
Authors’ contributions. S.K.J. and P.T.J.J. designed the study, all authors
conducted the research, D.M.C. processed samples, M.A.F. and
D.A.L. analysed country-level data, S.K.J. analysed individual-level
data and wrote the first draft; all authors contributed to the final
version of the manuscript.
Competing interests. We have no competing interests.
Funding. This research was supported by a fellowship from the David
and Lucile Packard Foundation, a seed grant from the Colorado State
University One Health Program, and a grant from the Deming Center
for Entrepreneurship.
Acknowledgements. We gratefully acknowledge R. Maseland for sharing
country-level data on T. gondii infection, S. Kavanaugh, D. Sharp,
B. Orr, B. Myles and R. Safran for assistance in ELISA development,
T. Riepe, T. Shah and S. Sonoda for assistance with data collection,
and K. Lafferty, M. Lappin, S. Vandewoude and two anonymous
reviewers for comments helpful in shaping the manuscript.
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... Men express lower and women higher altruism in the dictatorship game (Lindova et al., 2010). Infected subjects express higher entrepreneurship activity and have a higher tendency for risky behavior (Johnson et al., 2018), which might explain a higher risk of traffic accidents in the infected subjects (Flegr et al., 2002;Kocazeybek et al., 2009). Toxoplasma-infected women have also higher aggression (Cook et al., 2015) and self-aggression (Mathai et al., 2016;Postolache et al., 2021). ...
... While we expected differences in the political ideologies of infected men and women, we did not expect a higher score in economic equity in infected men. Typically, men affected with toxoplasmosis showed higher risk propensity and higher entrepreneurial activities (Johnson et al., 2018) more compatible with a competitive type of economy. The association of toxoplasmosis and the preference for an egalitarian economy in men needs to be better explored in future works. ...
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Humans infected by Toxoplasma gondii express no specific symptoms but manifest higher incidence of many diseases, disorders and differences in personality and behavior. The aim of this study was to compare the political beliefs and values of Toxoplasma-infected and Toxoplasma-free participants. We measured beliefs and values of 2315 responders via an online survey (477 Toxoplasma-infected) using the Political Beliefs and Values Inventory (PI34). This study showed Toxoplasma-infected and Toxoplasma-free participants of our cross-sectional study differed in three of four factors of PI34, scoring higher in Tribalism and lower in Cultural liberalism and Anti-Authoritarianism. We found sex differences in political beliefs associated with Toxoplasma infection. Infected women scored higher in tribalism and lower in cultural liberalism, compared with the Toxoplasma-free control group, while infected men scored higher in economic equity. These results fit with sexual differences in behavior and attitude observed after toxoplasmosis infection. Controlling for the effect of worse physical health and mental health had little impact, suggesting that impaired health did not cause these changes. Rather than adaptation to prevalence of parasites, as suggested by parasite-stress theory, the differences might be side-effects of long-term mild inflammatory reaction. However, to get clear picture of the mild inflammation effects, more research focused on different infectious diseases is needed.
... For example, infected men are more expedient, jealous, dogmatic, and suspicious, whereas infected women are more conscientious, persistent, warm-hearted, outgoing, and moralistic than non-infected subjects (Flegr, 2007). Higher financial risk behavior has also been reported in Toxoplasma-infected individuals (Johnson et al., 2018). In a recent study, Borráz-León et al. (2021a) reported that Toxoplasma-infected men scored higher in psychoticism and interpersonal sensitivity than non-infected men. ...
... Further research is also needed to study potential metabolic and physiological costs associated with Toxoplasma infection. For example, it is likely that the phenotypic changes of Toxoplasma-infected subjects such as lower facial FA, higher testosterone levels, and high-risk behaviors reported in this and other studies (Flegr, 2007;Johnson et al., 2018;Borráz-León et al., 2021a), may impose physiological costs to the host such as shortened life, reduced life quality during late adulthood, or increased predisposition to develop organic (e.g., hearth and pulmonary diseases) and mental diseases (e.g., depression, schizophrenia, bipolar disorder). Therefore, covariation between attractiveness, facial symmetry, changes in sex hormones and neurotransmitters, and the expression of physical and psychopathological symptoms, might be expected in genetically predisposed individuals. ...
Full-text available
Background Parasites are among the main factors that negatively impact the health and reproductive success of organisms. However, if parasites diminish a host’s health and attractiveness to such an extent that finding a mate becomes almost impossible, the parasite would decrease its odds of reproducing and passing to the next generation. There is evidence that Toxoplasma gondii ( T. gondii ) manipulates phenotypic characteristics of its intermediate hosts to increase its spread. However, whether T. gondii manipulates phenotypic characteristics in humans remains poorly studied. Therefore, the present research had two main aims: (1) To compare traits associated with health and parasite resistance in Toxoplasma -infected and non-infected subjects. (2) To investigate whether other people perceive differences in attractiveness and health between Toxoplasma -infected and non-infected subjects of both sexes. Methods For the first aim, Toxoplasma -infected ( n = 35) and non-infected subjects ( n = 178) were compared for self-perceived attractiveness, number of sexual partners, number of minor ailments, body mass index, mate value, handgrip strength, facial fluctuating asymmetry, and facial width-to-height ratio. For the second aim, an independent group of 205 raters (59 men and 146 women) evaluated the attractiveness and perceived health of facial pictures of Toxoplasma -infected and non-infected subjects. Results First, we found that infected men had lower facial fluctuating asymmetry whereas infected women had lower body mass, lower body mass index, a tendency for lower facial fluctuating asymmetry, higher self-perceived attractiveness, and a higher number of sexual partners than non-infected ones. Then, we found that infected men and women were rated as more attractive and healthier than non-infected ones. Conclusions Our results suggest that some sexually transmitted parasites, such as T. gondii , may produce changes in the appearance and behavior of the human host, either as a by-product of the infection or as the result of the manipulation of the parasite to increase its spread to new hosts. Taken together, these results lay the foundation for future research on the manipulation of the human host by sexually transmitted pathogens and parasites.
... Tachyzoites of T. gondii were detected in raw chicken eggs and the milk of sheep, goats, cows, and donkeys (reviewed in [15,16]). Currently, an estimated 2 million people globally are infected with T. gondii [17]. The parasite transmission can occur by consuming raw or undercooked meat containing tissue cysts, ingesting food or water contaminated with oocysts, or direct contact with oocysts shed in cat feces ( Figure 2). ...
... Severe toxoplasmosis cases in humans leads to retinochoroiditis and central nervous system disturbances [16]. Central nervous system disturbances might occur in humans, leading to an increased risk of car accidents, mental illness, neuroticism drug abuse and suicides (reviewed in [17]). In immunocompromised individuals, this infection phase can be fatal [14]. ...
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Toxoplasmosis is a zoonotic disease with veterinary and public health importance worldwide. Toxoplasma gondii infection in cetaceans is an indicator of land-to-sea oocyst pollution. However, there is a critical knowledge gap within the distribution of the T. gondii infection in cetaceans. To facilitate the global surveillance of this important zoonotic pathogen, we developed a field-deployable duplex insulated isothermal PCR (iiPCR) with automated magnetic bead-based DNA extraction for the on-site detection of T. gondii in stranded cetaceans. It targets the B1 gene of T. gondii combined with β2-microglobulin (B2M) gene of cetaceans as an internal control. Compared with the conventional qPCR assay, B1/B2M duplex iiPCR assay showed comparable sensitivity (21~86 bradyzoites in 25 mg of tissue) to detect spike-in standard of T. gondii DNA in cerebrum, cerebellum, skeletal muscle and myocardium tissues. Moreover, the overall agreement between the duplex iiPCR and qPCR was in almost perfect agreement (92%; 95% CI: 0.78–0.90; κ = 0.84) in detecting a synthetic spike-in standards. The B1/B2M iiPCR assay coupled with a field-deployable system provides a prompt (~1.5 h), feasible, highly sensitive and specific on-site diagnostic tool for T. gondii in stranded cetaceans. This platform provides one approach to evaluating aquatic ecosystem health and developing early warnings about negative impacts on humans and marine animals.
... As stated, the infection can amplify impulsivity and (in some cases) sensation-seeking, or risk-taking behaviors in humans. The predictions arise that it could be related to managerial, organizational (Houdek, 2017a(Houdek, , 2017b, or entrepreneurial roles (Johnson et al., 2018). Johnson et al. (2018) confirmed that toxoplasmosis infection is associated with a tendency to major in business-related fields among U.S. university students. ...
... The predictions arise that it could be related to managerial, organizational (Houdek, 2017a(Houdek, , 2017b, or entrepreneurial roles (Johnson et al., 2018). Johnson et al. (2018) confirmed that toxoplasmosis infection is associated with a tendency to major in business-related fields among U.S. university students. Moreover, the infected business major students were more likely to be interested in management and entrepreneurship (relative to other business subdisciplines such as accounting, finance, or marketing). ...
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This perspective shows how neurodiversity can increase public organizations’ innovations and output quality. Studies from business and entrepreneurship fields are used to argue that public organizations may prosper if they recruit neurologically atypical individuals. Their unique thinking styles, coping strategies, and life experiences can lead to public services innovation. The management of public organizations through neurodiversity programs may gain competencies benefiting all employees. However, the promotion of neurodiversity cannot be achieved without demanding changes in organizational culture. The article also illustrates the benefits of neurodiversity using the example of a neurogenerative disease (toxoplasmosis).
... Une méta-analyse regroupant huit études concluait à une association entre impulsivité et agressivité, avec la séropositivité pour T. gondii[332]. A noter toutefois qu'il s'agissait d'études de petite taille, qui contrôlaient imparfaitement l'ensemble des biais possibles.Une augmentation de la prise de risque, -qui serait le pendant de la néophobie et de l'anxiété diminuées chez le rongeur -, a également été rapportée chez des étudiants et des professionnels, notamment dans le cadre de l'entreprenariat et de la finance, ou après analyse des données de prévalence et de performances mondiales des entreprises (Global Entrepreneurship Monitor)[333]. A l'inverse, une petite étude cas-contrôle réalisée sur 79 étudiants ne retrouvait pas d'association entre séropositivité et prise de risque financier[334]. ...
Toxoplasma gondii est un parasite intra-cellulaire infectant près d’un tiers de la population mondiale. Généralement asymptomatique, la toxoplasmose est associée à une symptomatologie grave chez les patients immunodéprimés et dans le cas d’infection congénitale. Négligée par les pouvoirs publics, la phase chronique de l’infection a longtemps été sous-estimée. Cette méconnaissance entraîne donc des questions telles que quel est le meilleur protocole thérapeutique ? quelle est la meilleure stratégie diagnostique ? Récemment une stratégie de dissémination très avancée a été suspectée, sur la base de la théorie de la manipulation comportementale de l’hôte. Chez l’Homme, une telle manipulation peut avoir des effets majeurs cérébraux, neurologiques ou psychologiques. Quoi qu’il en soit, son impact sur le sommeil, qui constitue un index particulièrement sensible des fonctions cérébrales, est pour le moment inconnu. C’est pourquoi nous avons établi un modèle murin expérimental afin d’étudier les effets de Toxoplasma gondii sur le cycle éveil-sommeil. Nous avons montré que l’infection chronique par T. gondii était associée de manière persistante avec une augmentation de l’éveil et une diminution du sommeil, ce qui cadre avec la stratégie du parasite pour faciliter sa dissémination grâce à la prédation de son hôte. Nos résultats montrent pour la première fois les conséquences directes de l’infection toxoplasmique sur le comportement, pouvant avoir un impact majeur sur l’apparition de pathologies neuropsychiatriques et neurodégénératives.
... This is very likely an adaptation of T. gondii which serves to increase the probability of the host for becoming a prey of cats in which T. gondii finally reproduces sexually (Dubey and Jones 2008). There is evidence that T. gondii also influences the behavior of its human hosts, and a recent study addresses the possibility that human infection with T. gondii promotes the inclination of infected persons to the risky business of entrepreneurship (Johnson et al. 2018). In this case, this inclination would not be a personal trait but rather the consequence of an infection with T. gondii. ...
Full-text available
Bio-inspired design (BID) means the concept of transferring functional principles from biology to technology. The core idea driving BID-related work is that evolution has shaped functional attributes, which are termed “adaptations” in biology, to a high functional performance by relentless selective pressure. For current methods and tools, such as data bases, it is implicitly supposed that the considered biological models are adaptations and their functions already clarified. Often, however, the identification of adaptations and their functional features is a difficult task which is not yet accomplished for numerous biological structures, as happens to be the case also for various organismic features from which successful BID developments were derived. This appears to question the relevance of the much stressed importance of evolution for BID. While it is obviously possible to derive an attractive technical principle from an observed biological effect without knowing its original functionality, this kind of BID (“analog BID”) has no further ties to biology. In contrast, a BID based on an adaptation and its function (“homolog BID”) is deeply embedded in biology. It is suggested that a serious and honest clarification of the functional background of a biological structure is an essential first step in devising a BID project, to recognize possible problems and pitfalls as well as to evaluate the need for further biological analysis.
... Moreover, for human hosts, latent infection may also be associated with systemic changes in human personality (Lafferty, 2006). For example, Johnson et al. (2018) found that the entrepreneurial rate of T. gondii-positive individuals was 1.8 times higher than that of the control group (n = 197), suggesting that T. gondii infection may also weaken human's awareness of danger. These reports demonstrated a significantly elevated risk of anti-toxoplasma antibody seroprevalence among individuals diagnosed with psychiatric diseases such as schizophrenia. ...
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Toxoplasma gondii is known to have a complex life cycle and infect almost all kinds of warm-blooded animals around the world. The brain of the host could be persistently infected by cerebral cysts, and a variety of psychiatric disorders such as schizophrenia and suicide have been reported to be related with latent toxoplasmosis. The infected animals showed fear reduction and a tendency to be preyed upon. However, the mechanism of this “parasites manipulation” effects have not been elucidated. Here, we reviewed the recent infection prevalence of toxoplasmosis and the evidence of mental and behavioral disorders induced by T. gondii and discussed the related physiological basis including dopamine dysregulation and gamma-aminobutyric acid (GABA) pathway and the controversial opinion of the necessity for cerebral cysts existence. Based on the recent advances, we speculated that the neuroendocrine programs and neurotransmitter imbalance may play a key role in this process. Simultaneously, studies in the evaluation of the expression pattern of related genes, long noncoding RNAs (lncRNAs), and mRNAs of the host provides a new point for understanding the mechanism of neurotransmitter dysfunction induced by parasite manipulation. Therefore, we summarized the animal models, T. gondii strains, and behavioral tests used in the related epigenetic studies and the responsible epigenetic processes; pinpointed opportunities and challenges in future research including the causality evidence of human psychiatric disorders, the statistical analysis for rodent-infected host to be more vulnerable preyed upon; and identified responsible genes and drug targets through epigenetics.
... Research exploring the biological and neurological foundations of entrepreneurial action is a growing field within the domain of entrepreneurship scholarship (De Holan, 2014; Halko, Lahti, Hytönen & Jääskeläinen, 2017;Lahti, et al., 2018;Nicolaou & Shane, 2009;2014;Koellinger et al., 2010;Smith, 2010;van der Loos et al., 2011). Through varied means and methodologies, this stream of research is in the early stages of exploring how biological (e.g., Johnson et al., 2018;Lerner et al., 2021), neurological (e.g., Krueger & Day, 2010;Ortiz-Terán et al., 2013), psychophysiological (e.g., Lerner, Hatak, & Rauch, 2018) and genetic factors (e.g., Koellinger et al., 2010) shape different forms of entrepreneurial action. To date, several interesting insights have emerged through this research regarding the biological foundations of entrepreneurial action (Nicolaou & Shane, 2014). ...
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While management and entrepreneurship scholars have displayed comfort in and receptivity towards anthropomorphizing organizations, technologies, and even algorithms, our field has not yet grappled with a mountain of empirical evidence gathered over decades of research in the natural sciences that non-humans may behave entrepreneurially. For reflection and valuable perspective, our study relaxes the central assumption that entrepreneurial behaviors are the exclusive domain of human beings. Doing so invites fresh insights concerning the transversal nature of entrepreneurial action, the biological origins of innovation and entrepreneurship, the categorical assumptions demarcating the field of entrepreneurship, and the persistent emphases on intendedly rational conceptions of entrepreneurial action. The inspiration for our study involves “moving back from the species,” as E.O. Wilson advised. Through this “more distanced view” and by focusing on the reproducible benefits of entrepreneurship rather than narrower, human-centric conceptions of firm formation and profit generation, we find that the consideration of non-human behaviors contributes to the evolving definitions and future study of entrepreneurial action.
... In one follow-up study, it was also reported that students who majored in business and people who start their own businesses were more likely than controls to be infected with T. gondii. Several recent studies have also suggested that toxoplasmosis may be responsible for causing mild cognitive impairment in some otherwise healthy people [35][36][37][38][39]. ...
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This chapter introduces Toxoplasma gondii, the cause of toxoplasmosis. It discusses the many ways it can be transmitted and what is known about human infections, especially those affecting the brain, the pregnant uterus, and the eyes. It details the evidence linking this parasite to psychosis and estimates the percentage of psychosis cases that may be caused by it. It also briefly discusses the evidence linking toxoplasmosis to other conditions: epilepsy, brain cancer, rheumatoid arthritis, and motor vehicle accidents.
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This open access book analyzes the evidence linking Toxoplasma gondii to the increasing incidence of schizophrenia and bipolar disorder in the United States. Initially establishing that infectious agents are regularly transmitted from animals to humans, lead to human disease, and that infectious agents can cause psychosis, it then examines the protozoan parasite Toxoplasma gondii in detail. Infecting 40 million Americans, Toxoplasma gondii is known to cause congenital infections, eye disease, and encephalitis for individuals who are immunosuppressed. It has also been shown to change the behavior of nonhuman mammals, as well as to alter some personality traits in humans. After discussing the clinical evidence linking Toxoplasma gondii to human psychosis, the book elucidates the epidemiological evidence further supporting this linkage; including the proportional increase in incidence of human psychosis as cats transitioned to domestication over 800 years. Finally, the book assesses the magnitude of the problem and suggests solutions. Parasites, Pussycats and Psychosis: The Unknown Dangers of Human Toxoplasmosis provides a comprehensive review of the evidence linking human psychosis in the United States to infections of Toxoplasma gondii. It will be of interest to infectious disease specialists, general practitioners, scientists, historians, and cat-lovers.
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Latent infection with Toxoplasma gondii has repeatedly been shown to be associated with behavioral changes that are commonly attributed to a presumed increase in dopaminergic signaling. Yet, virtually nothing is known about its effects on dopamine-driven reward processing. We therefore assessed behavior and event-related potentials in individuals with vs. without latent toxoplasmosis performing a rewarded control task. The data show that otherwise healthy young adults with latent toxoplasmosis show a greatly diminished response to monetary rewards as compared to their non-infected counterparts. While this selective effect eliminated a toxoplasmosis-induced speed advantage previously observed for non-rewarded behavior, Toxo-positive subjects could still be demonstrated to be superior to Toxo-negative subjects with respect to response accuracy. Event-related potential (ERP) and source localization analyses revealed that this advantage during rewarded behavior was based on increased allocation of processing resources reflected by larger visual late positive component (LPC) amplitudes and associated activity changes in the right temporo-parietal junction (BA40) and left auditory cortex (BA41). Taken together, individuals with latent toxoplasmosis show superior behavioral performance in challenging cognitive control situations but may at the same time have a reduced sensitivity towards motivational effects of rewards, which might be explained by the presumed increase in dopamine.
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Milton Friedman once argued that profits are the chief purpose of business. Profits do matter, but today we know more about how business contributes to society. Good firms bring innovation to the marketplace, which facilitates their growth. Innovative, growing firms generate economic growth and employment, which, in turn, greatly improves people’s lives. In this paper I argue that the main goal of business is to develop new and innovative goods and services that generate economic growth while delivering important benefits to society. Steady economic growth generated through innovation plays a major role in producing increases in per capita income. Small changes in economic growth can yield very large differences in income over time, making firm growth particularly salient to societies. In addition to providing growth, innovative firms can supply important goods and services to consumers, particularly those at the base of the pyramid. Through innovation and growth firms can do untold good for society.
Found worldwide from Alaska to Australasia, Toxoplasma gondii knows no geographic boundaries. The protozoan is the source of one of the most common parasitic infections in humans, livestock, companion animals, and wildlife, and has gained notoriety with its inclusion on the list of potential bioterrorism microbes. In the two decades since the publication of the first edition of Toxoplasmosis of Animals and Humans there has been an explosion of knowledge concerning T. gondii and toxoplasmosis. Still used extensively as a cell model, its genome has recently been published making it a subject of even greater scientific interest. Keeping the organizational style that made the previous edition so popular and usable, this second edition has been completely revised and updated. New in the Second Edition: Expanded information on the cultivation, maintenance, and preservation of T. gondii Expanded information on the cell biology and molecular biology of the parasite Reviews all literature from the past 20 years for each domestic animal Summarizes information on the worldwide prevalence of toxoplasmosis in pregnant women and the devastating disease it can cause in newborn Written by one of the pioneers of the field, the book provides unique information on all known host types for this parasite. It distills the voluminous and potentially confusing scientific literature that has grown geometrically in the 20 years since the publication of the first edition into a comprehensive resource. The single author approach ensures a strong foundation in the biology and a seamless integration of topics. The new edition of this groundbreaking work is the only volume to cover toxoplasmosis of animals and humans thoroughly in one source. It supplies an entry point to further research by cutting through the morass of literature to identify the most relevant references.
Previously, we reported that Toxoplasma gondii (T. gondii)-seropositivity is associated with higher impulsive sensation seeking in younger men. As dopaminergic and serotonergic signaling regulate impulsivity, and as T. gondii directly and indirectly affects dopaminergic signaling and induces activation of the kynurenine pathway leading to the diversion of tryptophan from serotonin production, we investigated if dopamine and serotonin precursors or the tryptophan metabolite kynurenine interact with the T. gondii–impulsivity association. In 950 psychiatrically healthy participants, trait impulsivity scores were related to T. gondii IgG seropositivity. Interactions were also identified between categorized levels of phenylalanine (Phe), tyrosine (Tyr), Phe:Tyr ratio, kynurenine (Kyn), tryptophan (Trp) and Kyn:Trp ratio, and age and gender. Only younger T. gondii-positive men with a high Phe:Tyr ratio, were found to have significantly higher impulsivity scores. There were no significant associations in other demographic groups, including women and older men. No significant effects or interactions were identified for Phe, Tyr, Kyn, Trp, or Kyn:Trp ratio. Phe:Tyr ratio, therefore, may play a moderating role in the association between T. gondii seropositivity and impulsivity in younger men. These results could potentially lead to individualized approaches to reduce impulsivity, based on combined demographic, biochemical and serological factors.
A number of world literature reports indicate that a latent Toxoplasma gondii infection leads to development of central nervous system disorders, which in turn may lead to altered behavior in the affected individuals. T. gondii infection has been observed to play the greatest role in drivers, suicides, and psychiatric patients. Studies conducted for this manuscript involve a different, never before really reported correlation between latent T. gondii infection and ethanol abuse. A total of 538 decedents with a known cause of death were included in the study. These individuals were divided into three groups: the risky behavior group, inconclusively risky behavior group, and control group. The criterion for this division was the likely effect of the individual's behavior on the mechanism and cause of his/her death. The material used for analyses were blood samples collected during routine medico-legal examinations in these cases. The blood samples were used to measure anti-T. gondii IgG antibodies with an enzyme-linked immunosorbent assay (ELISA). Moreover, the following data were recorded for each decedent: sex, age, circumstances of death, cause of death, time from death to autopsy, and (if provided) substance abuse status (alcohol, illicit drugs). In those cases where blood alcohol level or toxicology tests were requested by the Prosecutor's Office, their results were also included in our analysis. Test results demonstrated a strong correlation between latent T. gondii infection and engaging in risky behaviors leading to death. Moreover, analyses demonstrated a positive correlation between the presence of anti-T. gondii IgG antibodies and psychoactive substance (especially ethanol) abuse, however, the causal relationship remains unclear. Due to the fact that alcohol abuse constitutes a significant social problem, searching for eliminable risk factors for addiction is extremely important. Our analyses provided new important information on the possible effects of latent T. gondii infection in humans.