Toxocara canis larvae reinfecting BALB/c mice exhibit accelerated speed of migration to the host CNS.

Using a small animal imaging system, migratory activity of Toxocara canis larvae stained by carboxyfluorescein succinimidyl ester (CFSE) was observed post primary infection (PPI) and post reinfection (PR) of BALB/c mice. Each infection was performed with 1,000 larvae per mouse. Primary infections were performed with labeled larvae, while for challenge infections the reinfecting larvae were stained by CFSE. The worm burden in mouse organs was determined during a period from 6 h to 21 days and 4 months PPI and PR. In comparison with primary infections that led to the first larvae appearance in the brain after 60 h, greatly accelerated migration of the parasites administered 3 weeks PPI to the CNS and eyes of challenged mice was noted-in both organs the larvae appeared 6 h PR. In all challenged mice, reinfecting larvae prevailed in the resident parasite population. Preliminary experiments with Toxocara cati larvae also revealed early brain involvement in primarily infected mice. Staining of T. canis larvae by CFSE had no effect on the development of a humoral antibody response against T. canis excretory-secretory antigens. In ELISA, elevated levels of specific IgG and IgG1 were noted on day 14 PPI and the levels of antibodies increased till the end of experiment. Reinfection induced an increase in the levels of both antibodies. In terms of optical density, IgG1 antibodies gave higher values in all sera examined. In ELISA for IgG antibodies, an increase in the avidity index of around 50% was detected 1 month PPI; higher-avidity antibodies were also detected in sera of reinfected animals.

Imaging of Toxocara canis larvae labelled by CFSE in BALB/c mice.

Mice are used most often as a model for human toxocariasis caused by Toxocara canis larvae. Variety of symptoms developing during the infection reflects behaviour of the larvae, which are able to escape from the intestine and further invade and damage various host organs. In order to find an approach enabling observation on parasite behaviour in mouse in vivo, we used an epifluorescence method and a small animal imaging system (SAIS). Larvae of T. canis were labelled by carboxyfluorescein succinimidyl ester (CFSE) which incorporated on the parasite gastrointestinal tract. Following infection of BALB/c mice by CFSE-labelled larvae it has been observed that staining had no influence on viability and further migratory activity of the parasites through the host organs (the intestine, liver, lungs and brain) where they were detected by SAIS until day 17 p.i. In addition, the dye did not affect larval antigenic activity as well as the development of related immune response. Imaging of parasites labelled by CFSE, therefore, may represent a promising way to study behaviour of T. canis larvae in a paratenic host.

The influence of RhD phenotype on toxoplasmosis- and age-associated changes in personality profile of blood donors.

Toxoplasma gondii, a parasite infecting 20-60% of humans in various countries, influences the behaviour of infected animal and human hosts. Infected human subjects have changes in several of Cattell's and Cloninger's personality factors. Recently, three independent studies have shown that Rh-positive subjects are protected against the T. gondii-induced changes of reaction times and increased risk of traffic accidents. Here we searched for evidence of similar effects of RhD phenotype on toxoplasmosis- or aging-associated changes in the personality profile of about 302 blood donors. We found that Rh-positive and Rh-negative subjects responded differently to toxoplasmosis. In addition to the already known effects of toxoplasmosis on novelty seeking, self transcendence, superego strength and protension, we also found effects of RhD phenotype on ego strength, protension, and praxernia, as well as opposite effects of toxoplasmosis on ego strength, praxernia, ergic tension and cooperativeness in Rh-positive and Rh-negative subjects. Moreover, our results indicate that RhD phenotype might influence not only the effect of toxoplasmosis but also the effect of aging on specific personality traits.

Higher perceived dominance in Toxoplasma infected men--a new evidence for role of increased level of testosterone in toxoplasmosis-associated changes in human behavior.

Toxoplasma is parasite of cats that uses any warm-blooded animals as intermediate hosts. It is known to induce shifts in behavior, physiology and even morphology of its intermediate hosts, including humans. The lower second to fourth digit ratio (2D:4D ratio) in infected man and women, and higher height in infected man suggest that sex steroid hormones like testosterone could play a role in these shifts. Here, we searched for another indirect indication for a higher postnatal testosterone level, i.e. increased perceived dominance and masculinity in infected men. We showed portrait pictures of 89 male students of which 18 were Toxoplasma-infected to 109 female students. When we statistically corrected for age, men with latent toxoplasmosis were perceived as more dominant (p=0.009) and masculine (p=0.052). These results support the idea that the higher level of testosterone could be responsible for at least some of the toxoplasmosis-associated shifts in human and animal behavior.

Gender differences in behavioural changes induced by latent toxoplasmosis.

There is growing evidence that the protozoan Toxoplasma gondii modifies behaviour of its intermediate hosts, including humans, where it globally infects about 20-60% of the population. Although it is considered asymptomatic in its latent stage, it was previously found to have remarkable and gender different effects on the personality factors A (warmth), G (rule consciousness), L (vigilance, mistrust) and Q3 (self-control, self-image) from Cattell's 16PF Questionnaire. We performed a double blind experiment testing 72 and 142 uninfected men and women, respectively, and 20 and 29 infected men and women, respectively, in order to verify these gender differences using behavioural experiments. Our composite behavioural variables Self-Control and Clothes Tidiness (analogue to the 16PF factors G--conscientiousness and Q3--self-control) showed a significant effect of the toxoplasmosis-gender interaction with infected men scoring significantly lower than uninfected men and a trend in the opposite direction in women. The effect of the toxoplasmosis-gender interaction on our composite behavioural variable Relationships (analogue to factor A--warmth) approached significance; infected men scored significantly lower than uninfected men whereas there was no difference in women. In the composite behavioural variable Mistrust (analogue to factor L), the pattern was affected by environment (rural versus urban). Possible interpretations of the gender differences are discussed.

Decreased level of novelty seeking in blood donors infected with Toxoplasma.

OBJECTIVES: Toxoplasma gondii, a parasitic protozoan, infects about 30 - 60% of people worldwide. Toxoplasma is known to induce behavioral changes and an increase of dopamine in mice. The presence of anti-Toxoplasma antibodies (latent toxoplasmosis) is also a risk factor for schizophrenia. Latent toxoplasmosis in men (male soldiers) is associated with lower novelty seeking. As the novelty seeking is supposed to negatively correlate with level of dopamine, the observed effect was interpreted as indirect evidence of increased dopamine levels in subjects with toxoplasmosis. However, it is also possible that the observed effect was caused by association of both novelty seeking and Toxoplasma infection with a third factor, e.g. size of place of residence. METHODS: Personality profile of 290 blood donors (205 men and 85 women) were measured by Cloninger's TCI (Temperament and Character Inventory) and their blood samples were assayed for the presence of anti-Toxoplasma antibodies. Difference between Toxoplasma-infected and Toxoplasma-free subjects was tested with ANCOVA method with gender, size of place of residence, and age as covariates. RESULTS: The present analysis revealed that lower novelty seeking was associated with latent toxoplasmosis both in men and women. The effect of infection on novelty seeking remained significant even after adjustment for size of place of residence (p<0.01). CONCLUSION: Decreased novelty seeking in Toxoplasma-infected subjects have been already confirmed in three independent populations (male soldiers and male and female blood donors). These findings suggest that the local inflammation-induced increase in dopamine in the brain of infected subjects can represent a missing link between toxoplasmosis and schizophrenia.