A parasite responsible for toxoplasmosis – Toxoplasma gondii – may be involved in the cause of around a fifth of schizophrenia cases in the US. This is according to a new study published in the journal Preventive Veterinary Medicine.

Share on Pinterest University of Pennsylvania researcher Greg Smith calculated that around a fifth of schizophrenia cases may be attributable to T. gondii infection.

The Centers for Disease Control and Prevention (CDC) estimate that around 60 million people in the US may be infected with T. gondii. Infection most commonly occurs through eating undercooked, contaminated meat, drinking contaminated water and coming into contact with cat feces that contain T. gondii.

Most people with T. gondii infection are unaware they have it; people with healthy immune systems are usually able to stop the parasite causing illness. But for those with weaker immune systems, such as older people, pregnant women and those with immune system disorders, the parasite can cause toxoplasmosis.

Toxoplasmosis a disease characterized by flu-like symptoms, including swollen lymph glands and muscle aches and pains. In severe cases, toxoplasmosis can cause damage to the eyes, brain and other organs.

Some studies, however, have linked T. gondii infection to mental health conditions. In 2012, for example, Medical News Today reported on a study linking T. gondi to increased risk of self-harm or suicide among new mothers.

More recently, studies have linked T. gondii infection to schizophrenia, and some have found that antipsychotic medication may even stop the parasite from replicating. But such research has been met with much criticism.

In this latest study, Gary Smith, of the School of Veterinary Medicine at the University of Pennsylvania, wanted to gain a better understanding of the link between T. gondii infection and schizophrenia.