Association between Toxoplasma gondii infection and psychiatric disorders: a cross-sectional study in China

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T. gondii infection is widespread worldwide, recent studies have shown that the seroprevalence of anti-Toxoplasma antibody ranges from 10 to 80%. The seroprevalence of Toxoplasma infection in China is relatively low, ranging from 2.3% to 35.6% among different populations and geographic regions8. Many studies have found a higher serological prevalence of T. gondii infection in psychiatric patients9,10,11and research on the relationship between T. gondii infection and psychiatric disorders has become a hot topic. China has 1.4 billion people and the latest research12 shows that the 12-month weighted prevalence of mental disorders (excluding dementia) in China is 9.3% (95% CI 5.4–13.3) and the lifetime weighted prevalence is 16.6% ( 95% CI 13.0–20.2). Considering the large number of mentally ill patients in China, research on the epidemiological status of T. gondii infection and the association between mental illness and T. gondii infection is particularly important and necessary.

The results of the present study showed that anti-Toxoplasma Both IgG and IgM antibodies in psychiatric patients and the general population were at low levels in the study region8,13,14.

The positivity rate of anti-Toxoplasma IgG antibodies in psychiatric patients were higher than those in the general population, which is similar to a previous study in Weihai, Shandong province, between 2011 and 201313. The results indicate that psychiatric patients in the study area should pay attention to the detection of T. gondii infection. There was no significant difference in the positivity rates of anti-Toxoplasma IgM antibodies between the general population and psychiatric patients, indicating that there is no difference in acute/recent infection of T. gondii among the general population and psychiatric patients in this study area. The seroprevalence of anti-Toxoplasma antibodies in psychiatric patients suggests that T. gondii infections in psychiatric patients in the study area are mostly recessive or long-term. However, the results contradict some research. Wang’s research14 in Zhejiang, China, showed that the seropositivity rates of anti-Toxoplasma IgG and anti-Toxoplasma IgM antibodies were significantly higher in psychiatric patients than in the non-psychiatric control group, which may indicate geographic differences in the epidemiological status of patients. T. gondii infection in psychiatric patients.

In this study, the positivity rate of anti-Toxoplasma IgM antibodies in the general population and patients with mental illness were lower than results published in China (Chen et al., 2019; Pan, M., et al., 2017; Chen, X., et al., 2019 ). This value is particularly lower than the search results in the neighboring region (Weihai) (Cong et al., 2015). Many investigations have focused on the association between T. gondii infection and psychiatric disorders, but the results of these studies are inconsistent. Many studies have reported that T. gondii HIV status is linked to mental illnesses such as schizophrenia, bipolar disorder, generalized anxiety disorder, obsessive-compulsive disorder, suicide, aggression and impulsivity15,16,17,18. However, others have failed to demonstrate significant associations between psychiatric disorders and toxoplasmosis.19.20. Anti-Toxoplasma IgM antibody is a marker of acute/recent exposure, persistent infection or reinfection21while previous studies have focused on combatingToxoplasma IgG antibody, which is a lifelong or latent exposure marker T. gondii infection and has a higher positivity rate than IgM antibodies. The latest research has revealed that chronic disease T. gondii infection leads to cortical neurodegeneration and causes CX3CL1, complement and microglia to interact, dividing and eliminating degenerated neurons22. Therefore, the analysis of anti-Toxoplasma The IgG antibody in this study is more significant.

After further analysis and comparison of different types of mental illness, the current study found that mania, schizophrenia, bipolar disorder, depression, and recurrent depressive disorder were all associated with higher rates of anti-Toxoplasma antibodies, except for dissociative depressive disorder. The seroprevalence of T. gondii infection in patients with bipolar disorder was significantly different from that in the general population, which is consistent with recently published meta-analysis results23.24. However, some items7,19,25 suggest that bipolar disorder is not associated with T. gondii infection. Therefore, the relationship between bipolar disorder and T. gondii the infection is still controversial and further research is needed.

Many studies suggest a link between T. gondii infections and schizophrenia, T. gondii become a potentially relevant etiologic factor in some cases of schizophrenia26,27,28and recent studies suggest that T. gondii infection may be an underlying component of the pathophysiology of schizophrenia29, which is consistent with our study, but some studies also come to the opposite conclusion. More rigorous studies are needed, from epidemiological studies to mechanistic studies to confirm the relationship between schizophrenia and T. gondii infection.

Most research has shown an absencee of an association between depression and T. gondii infection30,31,32. However, a potential association between depression/recurrent depressive disorder and T. gondii infection was found in this study, and the same result was also found in the Alvarado-Esquivel study 33.34. More research on the relationship between T. gondii infection and depression are needed to explain the different findings. Otherwise, T. gondii infection affects susceptibility and severity of depression in children, adolescents, and pregnant women35.36and patients with depression should pay attention to T. gondii infection. This study found a potential association between mania and T. gondii infection, but current research on the relationship between mania and T. gondii infection is still insufficient to draw definitive conclusions, and more attention should be given to manic patients.

Existing research has shown that people who live in rural areas are at increased risk of toxoplasmosis37, but no consistent results were found in our study. Studies have found differences in the seroprevalence of anti-Toxoplasma antibodies between men and women with psychosis38, which is inconsistent with our study. Further research is needed to explain these phenomena. In the present study, psychiatric patients had the lowest rate of positivity for anti-Toxoplasma IgG antibodies in the 21-40 age group, indicating that this age group had the lowest risk of T. gondii infection, which may be due to the strong body and immunity of this age group.

The subjects included in this study are mainly from the southwestern regions of Shandong province and parts of Henan and Jiangsu provinces, with a population of approximately 40 million in the study area. Shandong Daizhuang Hospital is the largest specialized mental hospital in Shandong Province. therefore, this study can accurately reflect the state of T. gondii infection among psychiatric patients in the study area and to some extent even in eastern China. The present study is a cross-sectional study, and cohort studies should be conducted in the future to better explain the internal link between psychiatric disorders and T. gondii infection.

This study mainly analyzed T. gondii infection in inpatient psychiatry due to difficulty in collecting baseline data from the general population and outpatient psychiatric patients. The population density in this study area is high and the included sample size is relatively small. Since only age information for the general population is available, more detailed personal information on the general population cannot be obtained for further analysis, and surveys with larger sample sizes and different population groups should be performed to assess several influencing factors. It’s widely believed that pregnant women shouldn’t have cats.39but research indicates that owning a cat during pregnancy or infancy does not confer an increased risk of later psychotic experiences in adolescence40. The extent to which cats are associated with T. gondii infection in patients with mental illness should be confirmed in future studies. Previous studies have suggested that anti-Toxoplasma antibody seropositivity persists throughout life41but as the research on the anti-Toxoplasma increase in antibodies and population-based analyses, some studies have suggested that persistent exposure to T. gondii is needed to maintain antibody levels42; so anti-Toxoplasma Antibody testing should be used as a routine test for assessing infection status and monitoring treatment in patients with mental illness.

Currently, many studies have been conducted on the relationship between T. gondii infection and psychiatric disorders, and there are still many controversies and uncertainties. First, the results are very different. This may be because different people in different regions will get different results. Second, it is difficult to determine and explain the causal relationship between T. gondii infections and psychiatric disorders. From the point of view of etiology and pathogenetic mechanism, it is assumed that T. gondii the infection will cause mental illness. From an epidemiological point of view, it is assumed that patients with mental illness are susceptible to T. gondii infection due to poor health awareness or weaker immunity. Therefore, research on the relationship between psychiatric disorders and T. gondii the infection should be analyzed in detail.

In summary, the seropositivity rate of T. gondii or the infection rate of T. gondii in the population of this region remains at a low level, but the seropositivity rate of T. gondii or the infection rate of T. gondii in patients with mental illness is maintained at a higher level than in the general population. Age and different types of mental illness may be associated with T. gondii infection. More scientific and rigorous research with populations and laboratories is necessary in our study area to determine the relationship between T. gondii infection and psychiatric disorders, in particular mania, schizophrenia, depression and recurrent depressive disorders.

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