What is it about?
We found that the probability of birth of a son is negatively correlated with the prevalence of toxoplasmosis in 94 particular countries. Toxoplasma prevalence was the third strongest predictor (of 10) of secondary sex ratio after son preference and fertility.
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Why is it important?
According to the Trivers-Willard hypothesis, female-biased sex ratio reflects impaired health and social status of women. The observed correlation, therefore, suggests that the effect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be. This suggests that the abundance of this parasite could be one of the most important ecological factors influencing the global variation of offspring sex ratio not only in humans but possibly also in many other animal species.
Perspectives
Our hypothesis on the negative effects of toxoplasmosis on public health was later confirmed by several large-scale studies. The effect of toxoplasmosis on sex ratio was also observed in one cross-sectional study on human (Kaňková, Š., Šulc, J., Nouzová, K., Fajfrlik, K., Frynta, D. and Flegr, J. (2007). Naturwissenschaften 94, 122–127) and one experimental study on laboratory mice (Kaňková, Š., Kodym, P., Frynta, D., Vavřinová, R., Kuběna, A. and Flegr, J. (2007). Parasitology 134, 1709–1717).
Jaroslav Flegr
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This page is a summary of: Do differences in Toxoplasma prevalence influence global variation in secondary sex ratio? Preliminary ecological regression study, Parasitology, April 2016, Cambridge University Press,
DOI: 10.1017/s0031182016000597.
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