New study links schizophrenia to cat ownership

Alan Martin June 16, 2015

A study has appeared in the Schizophrenia Research journal linking children growing up with cats to schizophrenia in later life. From analysis of a 1982 questionnaire completed by 2,125 families from the National Institute of Mental Illness, the researchers found that 50.6% of those with schizophrenia owned a cat in childhood.

New study links schizophrenia to cat ownership

The researchers note that “two previous studies suggested that childhood cat ownership is a possible risk factor for later developing schizophrenia or other serious mental illness,” and urged further research into the field to see if correlation is indeed causation. The two previous studies found a match of 50.9% (1992) and 51.9% (1997).

The NHS offers a more sceptical assessment of the research, highlighting that the “study is able to draw a link, but cannot prove cause and effect.”

But let’s assume that the hypothesis is real and that growing up in a house shared with cats can be a contributing factor to schizophrenia. Why would that be? t_gondii

The researchers point the finger of blame at a parasite found in infected cats. While Toxoplasma gondii (T. gondii) can infect any warm-blooded animal, felids are the only known host in which the parasite can reproduce.

In rodents, the presence of T. gondii has been shown to affect their behaviour: they lose their fear of cats, as the parasite attempts to travel to the host where it can really thrive. The parasite spreads from cats via their faeces, but it can also be found in undercooked meats, especially pork and lamb.

The parasite is said to cause subtle behavioural changes in humans too, but given that up to half the population of the world is thought to have been exposed to it, it isn’t considered too worrying a threat – unless you’re pregnant. It’s the reason behind pregnant women being urged to avoid cat litter: due to an unborn baby’s weaker immune system, the parasite can be passed on easily, making it a more serious threat.

Previously, T. gondii has been linked to poor school performance and increased suicide risk – quite the rap sheet for a single-cell parasite.

“T. gondii gets into the brain and forms microscopic cysts. We think it then becomes activated in late adolescence and causes disease, probably by affecting the neurotransmitters,” E. Fuller Torrey, a researcher from the Stanley Medical Research Institute, told The Huffington Post.

Of course, even if it’s proven without doubt that toxoplasmosis can cause schizophrenia in children – and that’s a big if – it’s debatable how much can be done. The NHS describes contact as being ‘unavoidable’, highlighting that the T. gondii parasite can survive in soil for months.

In addition, there’s the flipside of pet ownership to consider: cats have been shown to offer additional health benefits for the owner. One study suggested that keeping cats can reduce the risk of heart attack by a third, while the frequency of cat purrs is said to “improve bone density and promote healing.”

In short: the cat is your friend (or at least a neutral acquaintance). T. gondii less so.

Image: christigain and US Department of Agriculture used under Creative Commons