Toxoplasma infection and testosterone alterations
As mentioned in the previous text, changes in testosterone levels may represent the physiological mechanism underlying some of the observed associations in the domain of sexual behaviour and reproduction. However, the effects of Toxoplasma infection on testosterone levels in animals and humans are inconsistent, with some studies reporting increases and others decreases. This variability likely stems from differences in parasite strain, host genetics, infection intensity and species-specific responses (Abdoli 2014).
A recent meta-analysis of six animal studies found mixed results (Abdoli et al. 2024). Three studies in male animals (rats, mice and spotted hyenas) and two in female animals (mice and spotted hyenas) reported decreased testosterone levels, while two studies in male rats found increased levels. One study in female rats showed no significant change. Species differences may contribute to these inconsistencies, as rats are relatively resistant to toxoplasmosis, whereas mice are highly susceptible.
In humans, a systematic review and meta-analysis of 18 studies similarly found varying effects (Abdoli et al. 2024). Among 19 studies on males, 13 reported increased testosterone levels following latent toxoplasmosis, three found decreases and two showed no significant change. This meta-analysis indicated that infected males exhibited, on average, a 0.73-unit increase in testosterone, while infected females had a 0.55-unit increase compared to uninfected individuals. These findings suggest sex-specific effects, although some studies report no significant differences in hormone levels between infected and uninfected women (Borráz-LeÓn et al. 2021).
Testosterone is known to have immunosuppressive properties, which may be exploited by pathogens to enhance their chances of survival within the host (Braude et al. 1999, Roberts et al. 2004, Foo et al. 2017, Roved et al. 2017). A decrease of testosterone levels in infected hosts may therefore represent a compensatory response to immune alterations caused by Toxoplasma. During acute infection, lower testosterone levels could enhance immune function, increasing host survival. Conversely, elevat- ed testosterone in infected men may enhance visual and olfactory attractiveness (Flegr et al. 2008a,b), raising the possibility of parasite-driven manipulation to facilitate transmission from infected men to their uninfected sexual partners. If Toxoplasma does influence testosterone levels, the underlying purpose remains uncertain – whether to pro- mote sexual transmission or suppress host immunity for its persistence (Roved et al. 2017).
Publication Date: 2025-05-20