Influence of latent toxoplasmosis on the phenotype of intermediate hosts.

The influence of latent toxoplasmosis on the phenotype , especially on the behaviour, of intermediate hosts has been intensively studied since the mid-1990s. The number of papers dealing with this topic that can be found in the Web of Knowledge SM by using the combination of terms toxoplasm* AND (behavi* OR psychol* OR per-sonalit* OR psychiatri* OR schizophr*) is rapidly in-Most of these papers studied the influence of congenital or acute toxoplasmosis on the behaviour of laboratory infected mice; however, some of them also focused on the behavioural impacts of latent (or chronic in their terminology) toxoplasmosis. Even earlier, sporadic works suggested a relation between latent or acute toxoplasmosis and some psychiatric disorders, in particular schizophre-nia. The comprehensive review from 2007 (Torrey et al. 2007) lists 11 studies published in 1957–1980; however, several other studies, mostly case reports, that appeared in the 1940s and 1950s showed or suggested that acute toxoplasmosis was relatively often associated with pronounced psychiatric symptoms (Jírovec and Vojtěchovský 1957). The sharply increasing interest in the influence of latent toxoplasmosis on the host phenotype in the past two decades has both objective and subjective causes. The major objective cause is that about one third of the world population have been infected with Toxo-plasma gondii and latent toxoplasmosis that was until recently considered as asymptomatic has been shown to have the potential to have serious consequences for physical and psychical health. The strongest association was found between toxoplasmosis and schizophrenia, suggesting that toxoplasmosis might trigger this devastating psychiatric disorder in predisposed subjects or modulate the course of the disease. Latent toxoplasmo-sis seems to increase the risk of suicide (Arling et al. 2009) and four independent studies also found increased risk of traffic accidents in Toxoplasma gondii-infected subjects (Flegr et al. 2002, 2009, Yereli et al. 2006, Ko-cazeybek et al. 2009). Consequently, latent toxoplasmo-sis might be indirectly responsible for about one million deaths in traffic accidents, about as many deaths might result from increased risk of occupational injuries and possibly hundreds of thousands of deaths might be due to increased risk of suicide. Latent toxoplasmosis has a strong effect on reproduction in animal hosts of the parasite, including humans. It negatively influences the rate of development of early embryos (Flegr et al. 2005a, Kaňková and Flegr 2007) and shifts the sex ratio towards males in the early phase of Toxoplasma infection and towards females in the later phases (Kaňková …