Hidden danger? Dan Eaglesham

Scientists are getting catty — revealing a new study linking schizophrenia to cat ownership.

They speculate that the presence of a cat in a home may actually lead to the development of schizophrenia because of the Toxoplasma gondii, a single-cell parasite many cats carry.

"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," said E. Fuller Torrey, a scientist from the Stanley Medical Research who participated in the study. In earlier research he found that acute human infection with T. gondii can "produce psychotic symptoms similar to those displayed by persons with schizophrenia."

The study, published in Schizophrenia Research, discovered that cat ownership is "significantly more common" in families in which children are later diagnosed with schizophrenia or "another serious mental illness."

Analyzing the results of a 1982 National Institute of Health questionnaire, the researchers discovered that 50.6% of people who developed schizophrenia had a cat in their home during childhood. Similar results were found in two 1990 studies.

Research has discovered that T. gondii can enter the human brain by using a type of white blood cell in the immune system as a Trojan horse into the central nervous system. It can live in many different species but it can only complete its life cycle in cats when it is secreted in feline faeces.

Schizophrenia is a long-term mental illness that causes symptoms including hallucinations, delusions and changes in behaviour.

Some 1 in 100 people will experience schizophrenia in their lifetime. It's usually diagnosed between the ages of 15 and 35.