No Increased Detection of Nucleic Acids of CNS-related Viruses in the Brains of Patients with Schizophrenia, Bipolar Disorder, and Autism Spectrum Disorder

Viruses and psychiatric disorders: We have not crossed the borderline from hypothesis to proof yet (Review)

Most psychiatric disorders are heterogeneous and are attributed to the synergistic action of a multitude of factors. It is generally accepted that psychiatric disorders are the outcome of interactions between genetic predisposition and environmental perturbations, which involve psychosocial stress, or alterations in the physiological state of the organism. A number of hypotheses have been presented on such environmental influences that may include direct insults such as injury, malnutrition and hostile living conditions, or indirect sequelae following infection from viruses such as influenza, arboviruses, enteroviruses and several herpesviruses, or the differential expression of human endogenous retroviruses. It is known that the concept of viruses is far more extensive than their perception as mere agents of acute infections, or chronic debilitating diseases, such as AIDS or some forms of cancer. Notably, an apparent causal connection between viruses and the pathophysiology of diseases has been suggested; however, it remains unclear as to how to establish this causal connection. There are inherent difficulties in answering this question with certainty, which may be due to the multitude of genetic and environmental influences that can lead to psychopathology; the latent state of chronic infection exhibited by a number of neurotropic viruses; the late onset of psychiatric disorders with respect to the acute phase of viral infection at which detection tests would be successful; the complexity of the virome; and the existence of thousands of viral species. The present review aims to provide an outline of the conclusions that have thus far been reached regarding a possible association between viral infection and psychiatric disease, and the obstacles confronted during the quest for the truth behind the role of viruses.

Inflammation and viral infection as disease modifiers in schizophrenia

Numerous studies have now implicated a role for inflammation in schizophrenia. However, many aspects surrounding this aspect of the disease are still controversial. This controversy has been driven by conflicting evidence on the role of both pro-and anti-inflammatory factors and by often contentious findings concerning cytokine and immune cell profiles in the central nervous system and periphery. Current evidence supports the point that interleukin-6 is elevated in CSF, but does not support activation of microglia, resident macrophage-like cells in the brain. Furthermore, the mechanisms involving transit of the peripheral immune system factors across the blood brain barrier to central parenchyma have still not been completely elucidated. This process appears to involve perivascular macrophages and accompanying dendritic cells retained in the parenchyma by the chemokine and cytokine composition of the surrounding milieu. In addition, a number of studies have shown that this can be modulated by infection with viruses such as herpes simplex virus type I which may disrupt antigen presentation in the perivascular space, with long-lasting consequences. In this review article, we discuss the role of inflammation and viral infection as potential disease modifiers in schizophrenia. The primary viral hit may occur in the fetus in utero, transforming the immune response regulatory T-cells or the virus may secondarily remain latent in immune cells or neurons and modify further immune responses in the developing individual. It is hoped that unraveling this pathway further and solidifying our understanding of the pathophysiological mechanisms involved will pave the way for future studies aimed at identification and implementation of new biomarkers and drug targets. This may facilitate the development of more effective personalized therapies for individuals suffering with schizophrenia.