The relation of secondary sex ratio and miscarriage history with Toxoplasma gondii infection

Toxoplasmosis is one of the most prevalent parasitic diseases, caused by a coccidian protozoan, Toxoplasma gondii [1]. Prevalence of T. gondii infection varies 10–80% in various regions of the world. Large differences have also been reported in Iran, with a prevalence of 39.8% in Golestan Province and 28.8% in Kerman Province [2, 3]. The main routes of human infection include consumption of raw or undercooked meat containing tissue cysts and ingestion of oocysts via contaminated waters or vegetables [4]. Vertical transmission of rapidly dividing tachyzoites from the pregnant mother to developing fetus is the other route of human infection. This infection route could lead to abortion, chorioretinitis or serious developmental disorders such as hydrocephaly and microcephaly [5]. Therefore, the accurate diagnosis of acute maternal toxoplasmosis in pregnant women is critical [6]. The acquired T. gondii infection in immunocompetent hosts is usually benign and results in latent infections with formation of cysts in brain, lungs and other tissues [7]. Latent toxoplasmosis is clinically asymptomatic but may be complicated by the increased risk of psychiatric and neurological abnormalities and personality changes such as bipolar disorder, obsessive-compulsive disorder, recurrent migraine, cryptic epilepsy, autism, suicide attempt, homicide and brain tumor [8].

The secondary sex ratio (the ratio of males to females at birth) is nearly 0.51 in human [9], which is affected by factors including age of parents [10], stress, immunosuppression, paternal endocrine disruption such as diabetes [11‐13] and socioeconomic status of the parents [14]. Until now, three studies have assessed the effects of latent Toxoplasma infection on sex ratio at birth in humans and mice and all three found significant effects [15‐17]. In contrast, effects of latent toxoplasmosis on risk of miscarriage are still being discussed by researchers [18‐20]. Therefore, the present study was carried out to assess possible effects of T. gondii infection on secondary sex ratio and risk of miscarriage in 850 cord blood serum samples from delivered women in Tehran, Iran, 2014–2015.

Of 850 cord blood serum samples, 166 samples were positive for anti-Toxoplasma IgG; therefore, the overall anti-Toxoplasma antibody prevalence was 19.5% in this study. The average age of the participants was approximately 28.7 years with 95% confidence interval (28.4–29.1). Participants were divided into four age groups of ≤20, 21–25, 26–30 and ≥ 31. The majority of the pregnancies (334/850, 39.3%) occurred between 26 and 30 years of age. According to the age of women, the prevalence of anti-Toxoplasma IgG in 850 cord blood serum samples of participants was as follows: ≤ 20 age group, 7/27 (25.9%); early 20s, 43/189 (22.8%); late 20s, 60/334 (18%); and ≥ 31 age group, 56/300 (18.7%) (Fig. 1).

The highest frequency of miscarriage in Toxoplasma-positive and Toxoplasma-negative subjects was observed in ≥31 age group (Fig. 2), however, the association between the prevalence of toxoplasmosis and age of the women was not statistically significant (P = 0.4). Furthermore, no significant associations were seen between the miscarriage history and age of the women in seropositive participants (P = 0.15). Of 850 studied pregnant women, 444 delivered male neonates and 99 had a history of miscarriage.

The dormant stage of T. gondii infection in humans is characterized by the presence of tissue cysts in brain and other organs. From the clinical point of view, these life-long tissue cysts are almost asymptomatic in infected individuals [8]. In recent years, effects of asymptomatic latent toxoplasmosis in human life have been investigated [8]. Possible relationships of latent toxoplasmosis with mental disorders such as schizophrenia [25], Alzheimer^’s disease [26] and cognitive disorder [27] have been studied in humans and animal models. Increased reaction times [28] in Toxoplasma-infected individuals may explain the high-rate traffic accidents by these patients [29]. Toxoplasma gondii can affect personality of the infected patients [8]. The T. gondii infected men are nearly 3 cm taller than T. gondii free men, having further muscles and dominant faces. These differences may be associated with different testosterone levels in T. gondii positive and T. gondii negative men [30, 31]. Effects of T. gondii infection on endocrine and immune systems have been demonstrated repeatedly and their association with secondary sex ratio is not surprising [32]. According to results of the study by Flegr et al., latent toxoplasmosis has surprisingly serious effects on public health. Furthermore, T. gondii is one of the most important factors affecting variation of offspring sex ratio over the world [33].

Results of the present study have shown that T. gondii infection is significantly associated with having male neonates and that the association is statistically significant. The OR of having male neonates in T. gondii seropositive women was approximately 64% higher than that in seronegative women. A retrospective cohort study in Czech Republic (1996–2004) has shown that of 1803 neonates, the secondary sex ratio increased in 454 Toxoplasma-positive women (percentage of males = 0.608), compared to 1349 Toxoplasma-negative women (percentage of males = 0.527; P = 0.0027) [16]. In the current study, the OR of having male neonates increased in women with high-titer anti-Toxoplasma IgG as the value of 1.64 in seropositive women reached 2.10 in women with high-titer antibodies. A similar study by Kankova et al. (2007) showed that women with high concentration of anti-Toxoplasma IgG gave birth to 250 male neonates per 100 female neonates, while women with low concentration of anti-Toxoplasma of IgG gave birth more female than male neonates [16]. In experimental models, mice with T. gondii infection had a greater sex ratio, compared to control group [17]. Increased sex ratio could be explained by the effects of latent toxoplasmosis on immunosuppression mechanisms in mice and humans [34], as the secondary sex ratio is affected by significant modulation of immune responses and cytokine production in infected mice. Toxoplasma parasite could rescue male fetuses with developmental disorders by inducing immunosuppression mechanisms [35].

Seroprevalence of toxoplasmosis in women with abortion events has been recorded high (17–43.8%) in African and Asian countries [36‐38]. In the present study, relatively high seroprevalence (34.3%) of T. gondii infection was detected in cord blood serum samples of women with miscarriage history and the relationship between these two parameters was statistically significant. The odds of having miscarriage was approximately two and a half times higher for the seropositive women than for the seronegative women. The OR of having miscarriage increased to the value of 2.76 in low-titer seropositive women, compared to that in seronegative control group. The OR of having miscarriage in high-titer group was only 2.04. Moreover, the association between presence of anti-Toxoplasma IgG and miscarriage history in seropositive women was not statistically significant. Similar findings were reported by Sharf et al., 1973; Mahajan et al., 1976; Sahwi et al., 1995 and Al-Hamdani, 1997 [39‐42]. In a study by Alvarado-Esquivel et al. (2016) in Mexico, association of Toxoplasma infection and abortion in pregnant women of rural areas with high seropositivity rate was reported [43]. In 2011, Pavlinova et al. recorded 42.1% anti-Toxoplasma IgG seropositivity in 530 women with recurrent miscarriage which were significantly (P < 0.0004) greater than that in control groups (25.1%) [44]. In a study by Turbadkar et al., bad obstetric history (BOH) was recorded in 42.1% of Toxoplasma seropositive women [45]. In the present study, history of miscarriage in pregnant women and secondary sex ratio of offspring were statistically linked to T. gondii infection.