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Toxoplasma gondii & Human Phenotype

Compendium of Known Effects and Ongoing Research

ecological regression

Do differences in Toxoplasma gondii prevalence influence global variation in secondary sex ratio? Preliminary ecological regression study

September 27, 2016 99 Comments
Dama, S.M., Martinec Nováková, L., Flegr, J.
Parasitology 2016; 143, 1193–1203 doi:10.1017/S0031182016000597
Click for abstract
Sex of the fetus is genetically determined such that an equal number of sons and daughters are born in large populations. However, the ratio of female to male births across human populations varies signi fi cantly. Many factors have been impli- cated in this. The theory that natural selection should favour female o ff spring under suboptimal environmental conditions implies that pathogens may a ff ect secondary sex ratio (ratio of male to female births). Using regression models containing 13 potential confounding factors, we have found that variation of the secondary sex ratio can be predicted by seropreva- lence of Toxoplasma across 94 populations distributed across African, American, Asian and European continents. Toxoplasma seroprevalence was the third strongest predictor of secondary sex ratio, β = − 0·097, P < 0·01, after son pref- erence, β = 0·261, P < 0·05, and fertility, β = − 0·145, P < 0·001. Our preliminary results suggest that Toxoplasma gondii in- fection could be one of the most important environmental factors in fl uencing the global variation of o ff spring sex ratio in humans. The e ff ect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be.

Tagged: ecological regression, manipulation hypothesis, Secondary sex ratio, toxoplasmosis, Trivers Willard e ff ect

Physical health

Does prevalence of latent toxoplasmosis correlate with nation-wide rate of traffic accidents?

September 27, 2014 Leave a Comment
Flegr, J., Dama, M.
Folia Parasitologica 2014; 6, 485-494
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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 non - parametric 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 in - teraction 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

Tagged: correlation study, Disability Adjusted Life Years, ecological regression, manipulation hypothesis, Parasite, Toxoplasma

BehaviorCognitive functions

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