Oral Sex as a Potential Route for Toxoplasma Gondii Transmission: Experiment with Human Semen and Laboratory Mice Model.

PURPOSE: Toxoplasma gondii is one of the most widespread parasites in the human population globally. Several modes of its transmission have been proposed: some are well-researched and confirmed, others remain unconfirmed. One unconfirmed hypothesis pertains to potential transmission of Toxoplasma gondii via oral sex (fellatio) in humans. A recent study found tissue cysts in the semen of men with latent toxoplasmosis. Therefore, we aimed to test the hypothesis of Toxoplasma gondii transmission through oral sex experimentally. METHODS: Eighty-two laboratory mice were orally administered semen samples from 41 men with latent toxoplasmosis. These semen samples were examined for the presence of Toxoplasma gondii DNA using PCR. RESULTS: We detected Toxoplasma gondii DNA in three of the 41 semen samples from men with latent toxoplasmosis. Oral administration of semen samples to laboratory mice did not result in parasite transmission. CONCLUSION: We have not demonstrated the transmission of Toxoplasma to mice by oral exposure to semen from infected men. While this does not conclusively rule out the possibility of such transmission in humans, the results suggest that, if it does occur, this mode of transmission is likely infrequent.

Fertility of Czech Gay and Straight Men, Women, and Their Relatives: Testing the Sexually Antagonistic Gene Hypothesis.

One proposal for the persistence of homosexuality in the human population is the sexually antagonistic gene hypothesis, which suggests that the lower fertility of homosexual individuals, especially men, may be compensated by higher fertility of their relatives of the opposite sex. To test this hypothesis, we have collected data from 7,312 heterosexual men, 459 gay men, 3,352 heterosexual women, and 79 lesbian women mainly from Czechia. In an online survey, participants answered questions regarding their own as well as their parents' and grandparents' fertility. For men, we obtained no significant results except for higher fertility of gay men's paternal grandmothers, but the magnitude of this effect was very small. For the female sample, we recorded lower fertility of lesbian women's mothers and fathers. In line with our expectations, both gay men and lesbian women had lower fertility rates than their heterosexual counterparts. Our results are consistent with recent studies which likewise do not support the sexually antagonistic gene hypothesis.

Pandemic elevates sensitivity to moral disgust but not pathogen disgust.

The behavioral immune system, with disgust as its motivational part, serves as the first line of defense in organisms' protection against pathogens. Laboratory studies indicate that disgust sensitivity adaptively adjusts to simulated environmental threat, but whether disgust levels similarly change in response to real-life threats, such as a pandemic, remains largely unknown. In a preregistered within-subject study, we tested whether the threat posed by the Covid-19 pandemic would lead to increased perceived disgust. The perception of threat was induced by testing during two phases of the Covid-19 pandemic (periods of high vs. low pathogen threat). We found heightened levels of moral disgust during a "wave" of the pandemic, but the effect was not observed in the domain of pathogen or sexual disgust. Moreover, the age of respondents and levels of trait anxiety were positively associated with pathogen and moral disgust, suggesting that variation in disgust sensitivity may be based chiefly on stable characteristics.

Associations between nausea and vomiting in pregnancy, disgust sensitivity, and first-trimester maternal serum free ß-hCG and PAPP-A.

Elevated levels of nausea and vomiting in pregnancy (NVP) and disgust sensitivity have been observed in the first trimester and both are thought to have a protective function for the mother and her fetus. Their aetiology is not clear, however, with previous studies attributing elevated NVP and disgust to various factors including endocrine changes, immunological changes, and psychological variables. To date, no study has directly assessed the relationship between disgust and NVP. Here, we prospectively collected two independent samples (S1 and S2; n1 = 201, n2 = 391) of women in the first trimester of pregnancy, who completed the Index of Nausea, Vomiting, and Retching and the Disgust Scale-Revised. We also measured free ß-human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein A (PAPP-A) in maternal serum. Our results did not confirm any association between NVP and disgust; in addition, they indicate that NVP and disgust may have different proximate causes. Disgust sensitivity was significantly negatively correlated with free ß-hCG and (only in S1) with PAPP-A. In contrast, NVP was significantly positively associated with free ß-hCG levels and (only in S1) with PAPP-A. While low hCG levels seem to be an important indicator for activation of the behavioral immune system in the first trimester, increased hCG levels play a role in stronger symptoms of NVP, a result consistent with previous studies. Levels of PAPP-A are likely part of a larger network of immunological and endocrine responses and do not appear to provide sufficient information for predicting women's NVP and disgust sensitivity.

Disgust sensitivity in early pregnancy as a response to high pathogen risk.

Introduction: Considered a part of the behavioral immune system (BIS), disgust sensitivity is expected to be adjusting as a response to the actual level of the environmental health risks. Methods: In this preregistered study, we tested the hypothesis that disgust sensitivity would be higher during the COVID-19 pandemic compared to the pre-pandemic period in pregnant women. In this between-subject study with a longitudinal trend design, we administered the Disgust Scale-Revised to 200 pregnant women before the pandemic and to 350 pregnant women during the pandemic. Results: We found a small but significant effect of the pandemic on disgust sensitivity, such that higher disgust sensitivity was found in women pregnant during the pandemic. This effect was stronger in primiparae, however, the interaction between parity and the pandemic period was not significant. Disgust sensitivity decreased with age. No differences in terms of nausea and vomiting were found between the women pregnant before and during the pandemic. Discussion: Our findings indicate that although BIS is presumed to function as a complex mechanism to prevent health-threatening behaviors, its activation in pregnant women during the COVID-19 pandemic is rather weak.

Testing effects of partner support and use of oral contraception during relationship formation on severity of nausea and vomiting in pregnancy.

BACKGROUND: A recent study focusing on dietary predictors of nausea and vomiting in pregnancy (NVP) found that women with higher levels of partner support, and those who had used oral contraception (OC) when they met the father, both tended to report less severe NVP compared with previous non-users or those with less supportive partners. We provide a further test of these factors, using a large sample of women from four countries who retrospectively scored their NVP experience during their first pregnancy. METHODS: We recruited women who had at least one child to participate in a retrospective online survey. In total 2321 women completed our questionnaire including items on demographics, hormonal contraception, NVP, and partner support. We used general linear models and path analysis to analyse our data. RESULTS: Women who had used OC when they met the father of their first child tended to report lower levels of NVP, but the effect size was small and did not survive adding the participant's country to the model. There was no relationship between NVP and partner support in couples who were still together, but there was a significant effect among those couples that had since separated: women whose ex-partner had been relatively supportive reported less severe NVP. Additional analyses showed that women who were older during their first pregnancy reported less severe NVP, and there were also robust differences between countries. CONCLUSIONS: These results provide further evidence for multiple influences on women's experience of NVP symptoms, including levels of perceived partner support.

Longitudinal changes in disgust sensitivity during pregnancy and the early postpartum period, and the role of recent health problems.

Disgust is an essential part of the behavioral immune system, protecting the individual from infection. According to the Compensatory Prophylaxis Hypothesis (CPH), disgust sensitivity increases in times of immunosuppression, potentially including pregnancy. We aimed to replicate a previous study observing longitudinal changes in disgust sensitivity in pregnant women. Additionally, for the first time, we explored how recent health problems influence these changes. To do this, we obtained disgust sensitivity measures from 94 women in each trimester and in early postpartum. In contrast to the original study, where disgust sensitivity was highest in the first trimester, we found that overall and animal reminder disgust increased across pregnancy and after birth. In line with the CPH, women who were recently sick in the first trimester had elevated disgust sensitivity at that time. Although disgust sensitivity was significantly higher in the second trimester and postpartum period compared to the first trimester in mothers pregnant with a male fetus, the overall results regarding the effect of fetus sex on disgust sensitivity were mixed. It seems that changing levels of disgust sensitivity during pregnancy and postpartum result from a suite of physiological and psychological changes that occur during this sensitive period of a woman's life.

Presence of Toxoplasma gondii tissue cysts in human semen: Toxoplasmosis as a potential sexually transmissible infection.

OBJECTIVES: Toxoplasma gondii is a widely prevalent protozoan parasite in human populations. This parasite is thought to be primarily transmitted through undercooked meat and contamination by cat feces. Here, we seek to determine if Toxoplasma gondii cysts can be found within human semen. METHODS: We used a mixture of histological and immunofluorescence stains to visualize Toxoplasma gondii cysts in thin smears of human semen. Further, we probed for presence of bradyzoite-specific mRNA transcription using in-situ hybridization. RESULTS: We visualized Toxoplasma gondii cysts in ejaculates of immune-competent and latently infected human volunteers. We confirmed the encystment by probing transcription of a bradyzoite-specific gene in these structures. These observations extend previous observations of the parasite in semen of several non-human host species, including rats, dogs, and sheep. CONCLUSIONS: Toxoplasma gondii infection is a clinically significant infection, in view of its high prevalence, its purported role in neuropsychiatric disorders such as schizophrenia, as well as in the more serious form of congenital toxoplasmosis. Our demonstration of intact Toxoplasma gondii cysts in the ejaculate supports the possibility of sexual transmission of the parasite and provides an impetus for further investigations.

Redheaded women are more sexually active than other women, but it is probably due to their suitors.

Women with red hair color, i.e., 1-9% of female Europeans, tend to be the subject of various stereotypes about their sexually liberated behavior. The aim of the present case-control study was to explore whether a connection between red hair color and sexual behavior really exists using data from 110 women (34% redheaded) and 93 men (22% redheaded). Redheadedness in women, correlated with various traits related to sexual life, namely with higher sexual desire as measured by Revised Sociosexual Orientation Inventory, with higher sexual activity and more sexual partners of the preferred gender over the past year, earlier initiation of sexual life, and higher sexual submissiveness. Structural equation modelling, however, showed that sexual desire of redheaded women mediated neither their higher sexual activity nor their higher number of sexual partners. These results indirectly indicate that the apparently more liberated sexual behavior in redheaded women could be the consequence of potential mates' frequent attempts to have sex with them. Our results contradicted the three other tested models, specifically the models based on the assumption of different physiology, faster life history strategy, and altered self-perception of redheaded women induced by stereotypes about them. Naturally, the present study cannot say anything about the validity of other potential models that were not subjects of testing.

Oral contraceptive use during relationship formation and current relationship satisfaction: Testing the congruency hypothesis in couples attending pregnancy and fertility clinics.

According to the congruency hypothesis, relationship satisfaction is predicted by the congruency (or non-congruency) between current use of oral contraceptives (OC) and their use during relationship formation. This is based on findings that OC may alter women's mate preferences, so that attraction to their partner may have changed in non-congruent women. Indeed, some studies find that women in a non-congruent state were less sexually satisfied with their partner, although they were more satisfied in non-sexual aspects of the relationship. However, some other studies have produced null results, calling the hypothesis into question. In this study, we tested the congruency hypothesis in two samples of pregnant women, and in two samples of couples attending a fertility clinic. In all four samples, couples completed questionnaires on relationship and sexual satisfaction and the women also reported their previous and current contraceptive use. In one sample of pregnant women, we found that women who used OC during relationship formation were more sexually satisfied with their partner compared to women who did not use OC at that time; this pattern has previously been interpreted as supporting the congruency hypothesis in view of certain similarities in hormonal profile between OC use and pregnancy. We did not find any significant effect of OC use during relationship formation on sexual and relationship satisfaction in the other sample of pregnant women, either sample attending the fertility clinic, or in the male partners of any of our samples. Our results thus provide mixed support for the congruency hypothesis. Finally, we discuss recommendations for future studies such as use of within-subject designs and more structured assessment of sexual satisfaction.

The importance of being heterozygote: effects of RHD-genotype-sex interaction on the physical and mental health of a non-clinical population.

Human populations, especially European, are polymorphic in the RHD gene. A significant fraction of their members carry no copy of the coding section of RHD gene, which results in their Rh-negative blood type. Theoretically, this polymorphism should be unstable. Carriers of the less frequent allele are penalized by reduced fertility because of the immunization of RhD-negative mothers by their RhD-positive babies, which results in hemolytic disease of the fetus and newborn in their subsequent progeny. For about 90 years, some form of balancing selection has been suspected to sustain this polymorphism. Several recent studies showed that the RhD-positive heterozygotes express higher viability than both types of homozygotes. However, the genotype of subjects in these studies was estimated only by indirect methods. Here we compared the physical and mental health of 178 women and 86 men who were directly tested for their RHD genotype. The results showed that RhD-positive homozygotic women had worse and RhD-positive homozygotic men better physical health than RhD-negative homozygotes; the difference between RhD-negative homozygotes and heterozygotes was not significant. Our results confirmed that health of RhD-positive heterozygotes and homozygotes differ. Therefore, any result of the comparison of subjects with RhD-positive and RhD-negative phenotype depends on the heterozygote-to-homozygote ratio in the RhD-positive sample. It is, therefore, crucial to analyze the effects of RHD-genotypes, not phenotypes in future studies.

The Effects of Intrapartum Administration of Synthetic Oxytocin on Breastfeeding in the First 9 Months Postpartum: A Longitudinal Prospective Study.

Background and Objective: Synthetic oxytocin (synOT) is a widely used drug to induce or accelerate labor and to prevent postpartum hemorrhage. Although some studies indicate there are associations between intrapartum synOT and impaired breastfeeding initiation or earlier cessation, the long-term effects of synOT on breastfeeding are largely understudied. The aim of this study was to examine the effects of synOT on breastfeeding status during the first 9 months postpartum. Materials and Methods: The women were recruited from five maternity hospitals during prenatal medical checkups or postpartum hospital stay. They reported their breastfeeding status on discharge from maternity hospital (mean 4.54 days postpartum) (N = 439), at 6 weeks (N = 439), and at 9 months postpartum (N = 274). The data related to synOT administration were extracted from the medical records. Results: In the analysis adjusted for maternal age, parity, educational level, marital status, child's sex, delivery mode, and labor analgesia/anesthesia, intrapartum administration of synOT predicted a lower probability of exclusive breastfeeding on discharge from maternity hospital (odds ratio = 0.37; p = 0.006), but we observed no effect on breastfeeding status at 6 weeks or 9 months postpartum. Conclusion: Our results suggest that adverse effects of synOT on breastfeeding do not persist beyond the first postpartum days.

Relationship between Latent Toxoplasmosis and Depression in Clients of a Center for Assisted Reproduction.

Latent infection of the globally spread parasite Toxoplasma gondii in humans has been associated with changes in personality and behavior. Numerous studies have investigated the effect of toxoplasmosis on depression, but their results are inconsistent. Our study focused on the effect of latent toxoplasmosis on depression in men and women in association with their fertility. In 2016-2018, we recruited clients (677 men and 664 women) of the Center for Assisted Reproduction and asked them to complete a standardized Beck Depression Inventory-II. In women without fertility problems, we found higher depression scores in Toxoplasma-positive than in Toxoplasma-negative (p = 0.010, Cohen's d = 0.48). Toxoplasma-positive infertile men, on the other hand, had lower depression scores than Toxoplasma-negative infertile men (p ≤ 0.001, Cohen's d = 0.48). Our results are consistent with the previously described effects of latent toxoplasmosis, which seem to go in opposite directions regarding the effect on personality and behavior of men and women. Our results could be explained by gender-contrasting reactions to chronic stress associated with lifelong infection. This suggests that due to gender differences in the impact of latent toxoplasmosis, future studies ought to perform separate analyses for women and men.

Latent toxoplasmosis and vitamin D concentration in humans: three observational studies.

Numerous recent studies show that vitamin D deficiency potentiates various chronic physical and psychiatric disorders and diseases. It has been shown that a similar range of disorders is also associated with latent infection with Toxoplasma gondii (Nicolle et Manceaux, 1908). For instance, among cancer, diabetes and schizophrenia patients, we find a higher prevalence of both toxoplasmosis and vitamin D deficiency. Theoretically, therefore, vitamin D deficiency could be the missing link between toxoplasmosis and these disorders. We tested this hypothesis by searching for decreased vitamin D levels in the serum of subjects infected with T. gondii (furthermore called Toxoplasma-infected subjects) in two cross-sectional and one case-control study. Results of the first cross-sectional study (N = 72) suggest that Toxoplasma-infected neurasthenic patients have non-significantly lower levels of calcidiol than Toxoplasma-free patients (study A: P = 0.26 in women, P = 0.68 in men). However, two other studies (study B: N = 400; study C: N = 191) showed a non-significantly higher concentration of vitamin D in Toxoplasma-infected subjects than in Toxoplasma-free subjects both in men (study B: P = 0.70, study C: P = 0.55) and in women (study B: P = 0.64, study C: P = 0.12). Taken together, our preliminary results thus do not support the hypothesis that toxoplasmosis could be associated with vitamin D decrease.

Association between latent toxoplasmosis and fertility parameters of men.

BACKGROUND: About a third of people in the world are infected with Toxoplasma gondii. This parasite has been found in the reproductive organs and semen of males of many animal species as well as humans. The effects of toxoplasmosis on sperm count, motility and morphology were confirmed in rats. A higher prevalence of toxoplasmosis has been observed in infertile men. On the other hand, no significant effect of infection on semen parameters in men was found in one already published study. OBJECTIVES: To compare the prevalence of toxoplasmosis in men with and without semen pathology and to examine in detail the possible impact of infection on semen volume, sperm count, motility and morphology. MATERIALS AND METHODS: The pre-registered cross-sectional study included 669 men who visited the Centre for Assisted Reproduction in Prague from June 2016 until June 2018. RESULTS: The incidence of fertility problems was significantly higher in the 163 Toxoplasma-infected men (48.47%) than in the 506 Toxoplasma-free men (42.29%), τ = 0.049, P = 0.029. After correction for multiple tests, we found significantly lower sperm concentration, concentration of progressively motile sperm, and concentration of non-progressively motile sperm in Toxoplasma-positive men than in Toxoplasma-negative men using partial Kendall correlation with age controlled. In addition, toxoplasmosis correlated with sperm quality in smokers but not in non-smokers. DISCUSSION AND CONCLUSION: Our results suggest that latent toxoplasmosis affects certain semen parameters (sperm count and motility), but does not seem to affect sperm morphology and semen volume. Impairment of semen parameters may be either a side effect of the presence of Toxoplasma gondii in male reproductive organs or a product of manipulation activity of the parasite aimed to increase the efficiency of the sexual route of its transmission. Tobacco smoking also appears to exacerbate the negative impact of toxoplasmosis on semen parameters.

Male-to-Female Presumed Transmission of Toxoplasmosis Between Sexual Partners.

Toxoplasmosis is one of the most widespread human parasitoses in developed countries. Sexual transmission has been confirmed in several animal species, and indirect evidence suggests it may occur in humans. We compared the seropositivity to Toxoplasma gondii in couples who visited the Center for Assisted Reproduction in Prague from June 2016 to June 2018 and analyzed various risk factors including the serological status of sexual partner. By comparing the risk factors in men and women, we tested the hypothesis of male-to-female sexual transmission of toxoplasmosis. The prevalence of toxoplasmosis in women with infected male partners (25.6%; n = 156) was higher than in women with uninfected male partners (18.2%; n = 477; P = 0.045). Therefore, a partner's seropositivity seems to be a risk factor for infection in women (n = 593; prevalence ratio = 1.418; P = 0.045) but not in men (n = 573; prevalence ratio = 1.058; P = 0.816). Our results support the hypothesis of the sexual transmission of T. gondii from men to women. The risk may seem relatively low, but transmission can occur during unprotected sexual intercourse, which may be at the time of conception. Because of the risk of congenital toxoplasmosis, a lower risk of infection than that observed in our study can represent a serious health problem.

The role of balancing selection in maintaining human RhD blood group polymorphism: A preregistered cross-sectional study.

Maintenance of genetic polymorphism remains one of the big questions of evolutionary biology, which for a long time tended to be explained by balancing selection. This explanation was later criticized, but now is again accepted as an important mechanism in evolution. Human blood group systems seem affected by balancing selection especially strongly. In this preregistered study, we focused on stable coexistence of RhD-positive and RhD-negative subjects in a population. This is an evolutionary conundrum, because carriers of the less frequent negative allele suffer from lower fecundity due to haemolytic disease of the newborn affecting RhD-positive infants born to RhD-negative women. One explanation of persisting stability of RhD polymorphism points to heterozygote advantage. Over the past decade, numerous studies demonstrated that RhD-positive subjects score better than RhD-negative homozygotes in psychomotor tests and physical health-related variables. Still, evidence of better health and performance of heterozygotes is scarce and merely indirect. We compared the physical and mental health of 2,539 subjects whose RhD genotype was estimated based on their and their parents' RhD phenotype. We confirmed that RhD-negative homozygotes fare worse in terms of physical and mental health than subjects with RhD-positive phenotype and that RhD-positive heterozygotes enjoy better health than both homozygotes. For the first time, we demonstrated that RhD-positive homozygotes might suffer from worse health than RhD-negative homozygotes. Our results strongly support the hypothesis that RhD polymorphism is maintained by heterozygote advantage and that balancing selection may have played an important role in human evolution in this context and in general.

The effects of pre- and post-partum depression on child behavior and psychological development from birth to pre-school age: a protocol for a systematic review and meta-analysis.

BACKGROUND: Pre- and post-partum depression is a common mood disorder with detrimental effects on both mother and child. The aim of the proposed review is to summarize evidence related to the effects of both pre- and post-partum depression on child behavior and development from birth to preschool age. In particular, our review will address mutual relations between pre- and post-partum depression in order to determine whether pre- and post-partum depression predict child psychological outcomes independently, whether there is an effect of timing of depression on child outcomes, whether pre- and post-partum depression interact to affect child outcomes, and whether the effect of pre-partum depression is mediated by depression after child's birth. METHODS: We will include prospective longitudinal studies that report data about the effects of both pre- and post-partum depression on child psychological outcomes as published in peer-reviewed academic journals since January 1998. We will search EMBASE, MEDLINE, PsycARTICLES, PsycINFO, ISI Web of Science, Scopus, and Wiley Online databases to identify original research articles written in English. Two independent reviewers will screen search results in two stages: (i) titles and abstracts and (ii) full text. The first one will extract data into tables, while the latter will verify whether the data extracted are correct. We will assess the risk of bias in the selected studies using the Critical Appraisal Skills Programme (CASP), Cohort Study Checklist. The results of the review will be reported in a narrative form. If there are sufficient data available, a meta-analysis will be conducted using metaSEM package in R. DISCUSSION: The proposed review will be the first systematic review summarizing the effects of both pre- and post-partum depression on child psychological development and behavior from birth to preschool age. The results of such a review may contribute to a better understanding of mutual relations between pre- and post-partum depression in their effects on child outcomes. They may also shed light on what periods in early human development are most vulnerable to the effects of maternal depression. TRIAL REGISTRATION: PROSPERO CRD42018106269.

Increased 25(OH)D3 level in redheaded people: Could redheadedness be an adaptation to temperate climate?

About 1-2% of European population are redheaded, meaning they synthesize more pheomelanin than eumelanin, the main melanin pigment in humans. Several mutations could be responsible for this phenotype. It has been suggested that corresponding mutations spread in Europe due to a founder effect shaped either by a relaxation of selection for dark, UV-protective phenotypes or by sexual selection in favour of rare phenotypes. In our study, we investigated the levels of vitamin D precursor 25(OH)D3 (calcidiol) and folic acid in the blood serum of 73 redheaded and 130 non-redheaded individuals. In redheaded individuals, we found higher 25(OH)D3 concentrations and approximately the same folic acid concentrations as in non-redheaded subjects. 25(OH)D3 concentrations correlated with the intensity of hair redness measured by two spectrophotometric methods and estimated by participants themselves and by independent observers. In non-redheaded individuals, 25(OH)D3 levels covaried with the amount of sun exposure and intensity of suntan while in redheaded individuals, this was not the case. It suggests that increased 25(OH)D3 levels in redheaded individuals are due to differences in physiology rather than in behaviour. We also found that folic acid levels increased with age and the intensity of baldness and decreased with the frequency of visiting tanning salons. Our results suggest that the redheaded phenotype could be an evolutionary adaptation for sufficient photosynthesis of provitamin D in conditions of low intensity of UVB radiation in central and northern parts of Europe.

The effects of toxoplasmosis on sex ratio at birth.

Toxoplasmosis affects about one third of human population worldwide. It has a wide range of effects on the health, immunity, behaviour, and both prenatal and postnatal outcomes of infected hosts, including humans. Among these effects, stage of infection-specific shifts in secondary sex ratio were described about ten years ago both in humans and in artificially infected mice. In both women and female mice, in the early stage of infection the probability of giving birth of sons significantly increases, up to 260 sons to every 100 daughters. In the late stages of infection, the probability of giving birth to sons markedly decreases to as low as 78 to every 100 daughters. An ecological correlation study shows that the effect of latent toxoplasmosis on human population biology and demography can be large. In fact, the effect of prevalence of toxoplasmosis on a nationwide sex ratio was the third strongest effect from the effects of 15 factors included in the analysis. It has been suggested that toxoplasmosis-associated concentration of steroid hormones or glucose may be the proximal cause in the sex ratio shift. A more parsimonious explanation of the upward secondary sex ratio shift is found in a lower stringency of quality control of embryos, whose side-effect is increased survival rate of the more immunogenic male embryos in immunosuppressed infected females. The most parsimonious explanation of the downward secondary sex ratio shift relies on the Trivers-Willard hypothesis, which predicts an adaptive shift to more daughters in females with impaired health or lower socioeconomic status.