Understanding the Relationship of Chronic Toxoplasma Gondii Infection and Schizophrenia

Toxoplasma gondii is an important neurotropic parasite that can infect any warm-blooded animals including humans and causes Toxoplasmosis. The infection rate varies from 10-90 % world-wide depending on environmental or socioeconomic factors and geographic locations [1]. Due to its wide-spread nature and infection capacity, T. gondii has both medical and veterinary importance. After acute infection in human and warm-blooded livestock animals, T. gondii accomplishes its asexual stages life cycle through stage conversion of the parasite from fast replicating tachyzoite to slow replicating dormant bradyzoite particularly in brain and skeletal muscle [2]. This stage differentiation of the parasite brain and skeletal muscle permit them for establishing lifelong persistent infection. It has to be stressed that human can become infected primarily by ingesting undercooked or raw meats of infected livestock animals or eating contaminated foods and water [3].


Introduction
Toxoplasma Gondii is an important neurotropic parasite that can infect any warm-blooded animals including humans and causes Toxoplasmosis. The infection rate varies from 10-90 % world-wide depending on environmental or socioeconomic factors and geographic locations [1]. Due to its wide-spread nature and infection capacity, T. gondii has both medical and veterinary importance. After acute infection in human and warm-blooded livestock animals, T. gondii accomplishes its asexual stages life cycle through stage conversion of the parasite from fast replicating tachyzoite to slow replicating dormant bradyzoite particularly in brain and skeletal muscle [2]. This stage differentiation of the parasite brain and skeletal muscle permit them for establishing lifelong persistent infection. It has to be stressed that human can become infected primarily by ingesting undercooked or raw meats of infected livestock animals or eating contaminated foods and water [3].
European multicenter case control study showed that 30-63 % of acute infections of pregnant women are due to consumption of infected undercooked meats [4]. In immunocompetent host, primary infection is generally mild with flu-like symptoms whereas T. gondii infection can cause life threatening problems in immunocompromised patients for instance AIDS, transplant and cancer [5]. Furthermore, congenital toxoplasmosis can interfere brain development in fetus [6] which may provide significant impact on severe neurological damage or even death of the fetus. Neurological disorder like schizophrenia is present in ~1% people and ninth most common cause of disability over the world. The symptoms of the disease start from late teens to early adulthood, although the psychotic episodes can persist throughout the entire life of the patient. Till now, no single contributory driving force has been discovered; therefore, it is realistic only to explain some factors that were shown to be positively associated with schizophrenia. The well-known risk factors include: genetic predisposition, neurodevelopmental instability and environmental factors, including infectious agents [7,8]. In this study, we have deciphered the relationship of T. gondii infection and common neurological mental disorder schizophrenia.

Impact of T. gondii on schizophrenia
Schizophrenia is a chronic and severe neurological disease that affect nearly one percent of adult population worldwide [9]. People with this disease suffer from hallucination (false perception), delusion (beliefs that conflict with reality), depression, apathy, poor social activities and lack of speech [10]. The exact etiological factor for Schizophrenia has not been identified yet but it is widely accepted that mostly genetic and environmental factors are prominent cause for pathogenesis of the disease [11]. Recent evidence suggests that infectious agents can act as a high-risk factor for onset of schizophrenia Advances in Biotechnology & Microbiology [12]. Previous studies have shown that infection with virus e. g influenza, herpex simplex, rubella, polio and varicella zoster may contribute the development of schizophrenia [13].
Recently, T. gondii, an important neurotrophic protozoan parasite, has been identified as an important risk factor for developing symptoms of schizophrenia [14]. Thereafter a number studies has investigated the association of T. gondii and schizophrenia. has summarized 38 studies of T. gondii and schizophrenia and confirmed the increased prevalence of anti-T. gondii antibodies in schizophrenia patients (odd ratio 2.73, 95% CI) [15]. For instance, Hamidinejat and colleagues has shown that 57 % patients with schizophrenia carry anti-T. gondii IgG antibodies compared to healthy controls [16]. Another study conducted by Mortensen and colleagues suggest that early infection of T. gondii in newborn may develop schizophrenia in later stage of life [17]. Contrary, some other studies has failed to reveal the association of T. gondii infection with schizophrenia [18][19][20]. Although the role of T. gondii infection in developing schizophrenia is controversial in very few studies, the above majority studies nevertheless, confirm the positive correlation of T. gondii infection and development of psychiatric disease like schizophrenia. However, the mechanism of how the parasite develops the disease is remaining unknown.

Conclusion
Despite having few controversial findings, it can be said that there is strong correlation of T. gondii infection and schizophrenia. The correlation between T. gondii and schizophrenia might be explained in the way as T. gondii develop bradyzoite tissue cysts and persist in brain of infected patient's life time, thereby the parasite may somehow modulate neurological parameter which may directly or indirectly involved in that process. Further research is needed to find out the exact factors that determine the relationship of T. gondii infection in schizophrenic patients.