Toxoplasma Gondii infection: Does this parasitic disease alter the brain and behavior?

Many researchers believe that Toxoplasma gondii infection (Toxoplasmosis) can alter the human brain and behavior. However, recent research published this February in PLOS ONE suggests that there may be nothing to worry about after all. The study reports that there was little evidence that Toxoplasmosis gondii was related to increased risk of psychiatric disorder, poor impulse control, changes to personality or neurocognitive impairment, as previously found.

Toxoplasmosis is a disease caused by Toxoplasma gondii, a parasite that is present in around a third of the human population, as well as many other animal species. In humans, the primary source of infection is through contact with the feces of infected animals, especially domestic cats (the animal within which Toxoplasma gondii can reproduce). Infection can also occur through contact and ingestion of infected meat (especially pork), exposure to contaminated soil and water, or it can be passed on from a pregnant mother to her baby.

In rare cases, Toxoplasmosis can present with severe pathological symptoms, including diseases related to inflammation of the retina and choroid, inflammation and damage to heart muscle and inflammation of the brain, potentially leading to death. Despite this, most infected humans exhibit few or no physiological symptoms, suggesting little public health significance.

However, recent reports have suggested that infection might have previously unrecognized consequences in humans, with Toxoplasma infection being linked to a number of brain and behavior-related symptoms. Research has pointed to a correlation between Toxoplasma gondii infection and schizophrenia, stemming from the fact that some acute cases of infection resulted in hallucinations, a key feature of the disorder. There have been reported links between infection and major depressive disorder, poor impulse regulation (including violent and risk-taking behavior) and suicide attempts. There is also is some evidence that neurocognitive and personality differences exist following previous exposure to infection, including slower reaction times, poor attention and lower scores of novelty seeking.

The study, led by Karen Sugden of Duke University, tested the blood samples of 837 participants for antibodies against Toxoplasma gondii. From the 837 people who gave blood samples, 28% tested positive, indicating that they were infected with the parasite.

Results revealed that there was little evidence that Toxoplasma gondii infection results in increased susceptibility to neuropsychiatric disorders (schizophrenia and major depression), poor impulse control (suicidal behavior and criminality), changes in personality, or neurocognitive impairment. Although suicide attempt was marginally more frequent among individuals with previous exposure to infection.

This large study provides evidence against the possible link between Toxoplasma gondii infection and a variety of impairments. It also highlights the need for better research designs in order to guarantee that future research provides accurate insight into the possible influences of Toxoplasma gondii.