XXIV. T. gondii Influence on Host Behavior 2011
I.
Paper by Berdoy et al, 2000, Fatal attraction in rats infected with Toxoplasma gondii,
Proc. R. Soc. Lond. B 267: 1591-1594
A.
Manipulation hypothesis
1.
Parasite may alter host behavior
2.
Enhance parasite transmission rate
B.
T. gondii, cat, rat life-cycle
1.
Felines are only definitive hosts
2.
All mammals (including humans) serve as intermediate hosts
C.
Methods
1.
Used mice born to lab mice that had been bred with wild-type mice
2.
Inoculated 32 mice to parasite, but only 23 infected
3.
Control mice were sham-inoculated
4.
Followed mice behavior in 16 cell-maze with 4 odors
a.
Rat urine
b.
Neutral (= straw & water)
c.
Cat urine
d.
Rabbit urine (= control for mammal, non-predator)
D.
Results
1.
Figure 1
a.
Both preferred own odor area
b.
Uninfected rats avoided cat-scented areas
c.
Infected rats significantly (p= 0.002) less adverse to avoiding cat
odor
d.
Behavior alterations confined to cat odor.
2.
Figure 2
a.
Behavior of 25% most active rats
b.
Infected rats showed a preference for areas with cat odor
E.
Discussion
1.
Altered behavior confined to predator=s odor
2.
Not caused by destruction of olfactory capability
3.
1974 study of T. gondii in humans, 1974
a.
Prevalence
(1)
22% England
(2)
84 % France
b.
Altered personality & IQ levels
4.
Omnivores paradox
a.
Normal rat behavior is a conflict between pronounced neophobic
reactions and strong exploration tendencies
b.
Typical of opportunistic omnivore
II.
Paper by Flegr, 2007, Effects of Toxoplasma on Human Behavior, Schizoprenia Bulletin
33:757-760.
A.
Compared human behavior traits to levels of antibodies to T. gondii
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1.
Infected women
a.
Higher warmth
b.
Outgoing personalities
c.
Moralistic
2.
Infected men
a.
Disregard rules
b.
Suspicious
c.
Dogmatic
B.
Data from automobile accidents
1.
Prague, Czech Republic
a.
Experimental: Collected blood from 146 hospital patients who
were judged to have caused an accident.
b.
Control: 446 random blood samples
c.
Toxoplasma-infected subjects have a 2.65 times higher risk of
traffic accidents than Toxoplasma-free subjects
2.
Turkey
a.
Antibodies to T. gondii in drivers (n= 185) involved in traffic
accidents
IgG = 24.3%; IgM = 3.2%
b.
Age-matched controls
IgG = 6.5%; IgM = 0.5%
C.
Although house cats rarely eat people, in Africa, primates account for a large
proportion of leopards’ diet
III.
Paper by Lafferty, K. 2006, Can the common brain parasite, T. gondii, influence human
culture?, Proc.Roy. Soc. B., 273: 2749-2755.
A.
Prevalence of T. gondii can explain a statistically significant portion of variance
in neuroticism among human populations/cultures.
Data Slide: Fig 1. Association between two measures of aggregate neuroticism and the
prevalence of T. gondii
B.
Mice infected with T. gondii have elevated levels of dopamine, a neurotransmitter
known to alter novelty-seeking behavior.
Data Slide: Fig. 2: Association between the cultural dimension of uncertainty avoidance and the
prevalence of T. gondii
C.
Factors affecting risk of exposure to T. gondii
1.
Climate: Oocysts live longer in humid, low altitude regions with
infrequent freezing and thawing.
2.
Behavior or living conditions
a.
Dwelling with cats
b.
Working with soil
c.
Poor hygiene
3.
Cultural cuisine that includes undercooked meat
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