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In recent years there has been a surge in interest in the idea that human behaviour might be sometimes manipulated by microscopic parasites, as this has been observed happening in many other species. Perhaps the most famous example is the brain parasite toxoplasma gondii, which manipulates rodents’ behaviour to make them less fearful of cats. It does this because toxo only reproduces inside a cat’s stomach – by making the rodents less fearful, they are more likely to be eaten and ‘deliver their payload’ to where it needs to be.

Some have suggested that humans too might be affected by toxo, an idea that sounded even more plausible when last year researchers found that chimpanzees with toxo seem to be less fearful of a feline predator, the leopard. Previous to that study, other research had implicated toxo as the possible cause of a range of psychological effects in humans, from delayed reaction time right through to suicidal thoughts.

But a new piece of research has now thrown doubts over that idea, with scientists finding no evidence that cat ownership contributes to mental health problems in teenagers:

Congenital or early life infection with Toxoplasma gondii has been implicated in schizophrenia aetiology. Childhood cat ownership has been hypothesized as an intermediary marker of T. gondii infection and, by proxy, as a risk factor for later psychosis. Evidence supporting this hypothesis is, however, limited.

We used birth cohort data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to investigate whether cat ownership in pregnancy and childhood (ages 4 and 10 years) was associated with psychotic experiences (PEs) in early [13yo] and late [18yo] adolescence, rated from semi-structured interviews. We used logistic regression to examine associations between cat ownership and PEs, adjusting for several sociodemographic and socioeconomic factors, household characteristics and dog ownership.

Cat ownership during pregnancy was not associated with PEs at age 13 years or 18 years. Initial univariable evidence that cat ownership at ages 4 and 10 years was associated with PEs at age 13 years did not persist after multivariable adjustment. There was no evidence that childhood cat ownership was associated with PEs at age 18 years.

The researchers concluded that while pregnant women “should continue to avoid handling soiled cat litter, given possible T. gondii exposure”, overall the study “strongly indicates that cat ownership in pregnancy or early childhood does not confer an increased risk of later adolescent PEs.”

So there’s one less excuse to use when your child asks you for a kitten…

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