Infectious agents

How are infectious agents related to risk for schizophrenia?

Increased exposure to infections prior to the onset of schizophrenia has been recognised, which suggests infections may be involved in its aetiology. Potential mechanisms for this association include direct impacts of infections on the brain, immune activation, inflammatory cytokines, and alterations in the gut microbiota. This topic summarises the available evidence for the risk of developing schizophrenia following exposure to infectious agents, both before and after birth. For further information, please also see the maternal illness, infectious agents and immunological changes topics.

What is the evidence for infectious agents as risk factors for schizophrenia?

Moderate to high quality evidence found a small increased risk of schizophrenia in people exposed to childhood infections, particularly central nervous system viral infections. The effect sizes increased with increasing number of hospitalisations and decreased with increasing age of exposure (up to 10 years old).

Moderate quality evidence from prospective cohort studies, but not retrospective case-control studies, showed a small but significant association between gastroenteritis exposure and later development of schizophrenia. There was also a small increase in Toxoplasma gondii antibodies found before the development of schizophrenia. Toxoplasma gondii is a parasitic protozoa, hosted by domestic cats and other warm-blooded animals, including humans.

Moderate to high quality evidence suggests a small increased risk of psychotic disorders (mostly schizophrenia spectrum or non-affective psychosis) following exposure to herpes simplex type 2 in utero. Lower quality evidence suggests exposure to toxoplasma gondii or genitourinary infections in utero may also be associated with increased risk of psychotic disorders. No significant risk was found following exposure to herpes simplex type 1, influenza (in any trimester), or cytomegalovirus in utero.

April 2022

Image: ©Andrey Burmakin – Fotolia –

Last updated at: 3:31 pm, 25th April 2022
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Fact Sheet Technical Commentary

NeuRA Libraries

Title Colour Legend:
Green - Topic summary is available.
Orange - Topic summary is being compiled.
Red - Topic summary has no current systematic review available.