Body height, body mass index, waist-hip ratio, fluctuating asymmetry and second to fourth digit ratio in subjects with latent toxoplasmosis

Abstract

Between 20% and 60% of the population of most countries are infected with the protozoan Toxoplasma gondii. Subjects with clinically asymptomatic life-long latent toxoplasmosis differ from those who are Toxoplasma free in several behavioural parameters. Case-control studies cannot decide whether these differences already existed before infection or whether they were induced by the presence of Toxoplasma in the brain of infected hosts. Here we searched for such morphological differences between Toxoplasma-infected and Toxoplasma-free subjects that could be induced by the parasite (body weight, body height, body mass index, waist-hip ratio), or could rather correlate with their natural resistance to parasitic infection (fluctuating asymmetry, 2D : 4D ratio). We found Toxoplasma-infected men to be taller and Toxoplasma-infected men and women to have lower 2D : 4D ratios previously reported to be associated with higher pre-natal testosterone levels. The 2D : 4D ratio negatively correlated with the level of specific anti-Toxoplasma antibodies in Toxoplasma-free subjects. These results suggest that some of the observed differences between infected and non-infected subjects may have existed before infection and could be caused by the lower natural resistance to Toxoplasma infection in subjects with higher pre-natal testosterone levels.

Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels around the time of conception

“…A number of reports have given grounds for supposing that the testosterone (T) concentrations of infected people are high. Flegr et al (2005) reported that infected men and women (as contrasted with uninfected controls) have lower values of Table 1 References substantiating that the given cancers are associated with (a) low offspring sex ratios and (b) hormone profiles ex hypothesi responsible for those sex ratios…”

Differences in the 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line

“…Also, we confirmed the significant differences between Toxoplasma-negative and Toxoplasma-positive individuals in the left-handed 2D : 4D ratio (cf. Flegr et al 2005).…”

“…In the case of the 245 biology students for which results of the serological test for toxoplasmosis were available, we also tested for the effect of Toxoplasma infection on the 2D : 4D ratio (documented in Flegr et al 2005). Next, we fitted the full-factorial GLM model with the length of the 2nd finger as a dependent variable, the length of the 4th finger as a covariate, sex and eventually Toxoplasma infection status as factors, and searched for a significant effect of these factors and their interactions with the covariate.…”

Potential solutions to problems posed by the offspring sex ratios of people with parasitic and viral infections

“…this parasite is common in human beings, between 20% and 60% of the populations of most developed countries being infected (Flegr et al 2005a). Kaňková et al (2007a) reported that (as contrasted with uninfected controls), infected women are more likely to produce sons (p = 0.001), and that the offspring sex ratio (proportion male) increases with the concentration of anti-Toxoplasma antibodies in T. gondii-positive mothers (p = 0.001).…”

“…Flegr et al (2005a) reported that infected men and women (as contrasted with uninfected controls) have lower values of Manning's R (where R = 2D/4D) where 2D is the length of the 2nd digit, and 4D the length of the 4th digit. Manning had reported that low values of R are associated with high circulating t values (Manning et al 1998, Manning 2002.…”