Latent toxoplasmosis is the most widespread parasite infection in developed and developing countries. I'he prevalence of Toxoplasma gondii infection varies mostly between 20 to 80% in different territories. This form of toxoplasmosis is generally considered to be asymptomatic. Recently published results, however, suggest that the personality profiles of infected subjects differ from those of uninfected controls. These results, however, were obtained on non-standard populations (biologists or former acute toxoplasmosis patients). Here we studied the personality profiles of 191 young women tested for anti-Toxoplasma immunity during gravidity. The results showed that the differences between Toxoplasma-negative and loxoplasma-posilive subjects exits also in this sample of healthy women. The subjects with latent toxoplasmosis had higher intelligence, lower guilt proneness, and possibly also higher ergic tension. The difference in several other factors (desurgency/surgency, alaxia/protension, naiveté/shrewdness, and selfsentiment integration) concerned changes in the variances, rather than the mean values of the factors.
Latent toxoplasmosis is probably the most common protistan parasitic disease with many indirect negative impacts on human health. One of the important impacts is impaired psychomotor function leading to reduced driving efficiency in Toxoplasma-seropositive subjects. Numerous case-control studies have established a positive relation between the seroprevalence of Toxoplasma gondii (Nicolle et Manceaux, 1908) and probability of traffic accidents in study populations. The prevalence of toxoplasmosis varies between populations according to local geographical conditions, hygienic practices and kitchen habits. Similarly, we see a striking variation in the incidence of traffic accidents across countries. Hence, we compiled the largest ever data set on the seroprevalence of toxoplasmosis and tried to understand its role in traffic accident-related deaths and disabilities across 87 countries. Simple nonparametric analysis showed a positive and strong relation of T. gondii seroprevalence and traffic accident related disabilities. Further, we conducted multivariate analysis to control for confounding factors. After controlling for wealth, geographical latitude, health of population, length of roads and number of vehicles, the correlation disappeared. When the frequency of RhD negativity and its interaction with toxoplasmosis were included into the model, the effects of toxoplasmosis seemingly returned. However, the analysed data suffered from the problem of multicollinearity. When a proper method of analysis, ridge regression, was applied, the effects of toxoplasmosis prevalence and RhD negativity frequency disappeared again. The existence of a strong correlation between the prevalence of toxoplasmosis and health of population in particular countries, which was the probable cause of multicollinearity and possible reason for the negative result of the present study, suggests that ''asymptomatic'' latent toxoplasmosis could have a large impact on public health.
An effect of parasites on host behaviour was tested on the toxoplasma-human model. Three hundred and thirty-eight (338) people were assessed with Cattell’s personality questionnaire and then tested for Toxoplasma gondii infection with a delayed type hypersensitivity test for Toxoplasma. A highly significant correlation between chronic toxoplasmosis and two personality factors (G- Low Superego Strength and L- Protension) was found (p = 0.0032 and 0.0020, respectively). A correlation of the intensity of the personality factor-shifts with the duration of the infection (estimated from antibody titer) suggests that toxoplasmosis induces the shift in human personality, rather than the personality factors G and I. influence an acquisition rate of Toxoplasma gondii infection.
Parasites commonly manipulate host behaviour to increase transmission success between hosts. While most behavioural changes comprise slight alterations to host activity patterns and habitat use, some represent impressive alterations to routine behaviour which, while having direct positive effects on parasite transmission, compromise host survival. Here, we report conspicuous risky behaviour in an African annual killifish, Nothobranchius furzeri, infected by metacercariae of a strigeid trematode, Apatemon sp., residing in their cranial cavity. We demonstrate a striking contrast in the spatial and temporal behavioural responses of fish from populations naturally infected with Apatemon sp. and fish from two control populations with either a similar baseline parasite fauna but lacking Apatemon, or an overall low-level of infection. During routine activity, fish from Apatemon-infected populations positioned themselves just below the water surface, while other fish spent most of their time near the bottom. During a simulated avian attack, killifish from Apatemon-infected populations jumped above the water surface, moved in an uncoordinated manner, and rotated in the upper water layer, while fish from the control populations rapidly escaped into deeper water and ceased moving. The same self-exposing behaviour (jumping out of the water and lying on floating lily pads for extended periods) was also observed under natural conditions. Such behaviour greatly facilitates location of Apatemon-infected host fish by avian definitive hosts, especially in turbid pools. Moreover, the nothobranchiid killifish host's own life history, i.e. an extremely short lifespan limited to several months, may represent an important driver in the evolution of behavioural manipulation.
Quantitative data are presented on the spatial distribution of metacercariae of the digenean trematode Diploslomum phoxini (Faust, 1918) in the brains of minnows, Phoxinus phoxinus (Linnaeus, 1758), from two Scottish populations. Sequential examination of serial histological sections revealed metacercariae to be unevenly distributed throughout the brain, aggregating in specific regions including the cerebellum, the medulla oblongata and the optic lobes. In addition, a number of metacercariae were found in the anterior part of the spinal cord. The inferior lobe of the cerebellum, pituitary, olfactory lobes and olfactory bulbs were largely free of metacercariae. Reasons for the uneven distribution of metacercariae within the brains of infected minnows are discussed, including the possibility that the parasite may have evolved to enhance its transmission to subsequent hosts by aggregating in regions known to be important in the control of the host’s antipredator responses.