A COMMON parasite that lives in cats and was thought to be harmless to humans may be causing people to attempt suicide, scientists have found.
New research led by a Swedish associate professor at Michigan State University has found infection with Toxoplasma gondii is linked with a seven-times higher risk of suicide.
Scotland has the highest suicide rate in the UK with 772 people taking their own lives last year. Toxoplasma is also thought to be prevalent in Scotland.
The researchers studied 84 Swedish adults using a suicide assessment scale to estimate the future risk of a suicide attempt.
They also took blood samples to check for the presence of antibodies indicating previous infection with Toxoplasma.
Associate Professor Lena Brundin said: “We found that if you are positive for the parasite, you are seven times more likely to attempt suicide.”
The research adds to work linking infection with Toxoplasma gondii and suicide. However, this was the first study to look at whether infection could be used to predict suicide risk.
Toxoplasma gondii is a parasite that lives in cats. It multiplies in the stomach, and large numbers of parasites are shed in cat faeces.
People can become infected by drinking water contaminated with the parasite, and to some degree from handling cat litter.
The parasite can infect other mammals as well, so eating undercooked meat is another potential source of infection.
If infected, most people experience mild flu-like symptoms, but the parasite can cause severe illness in those with weak immune systems, or in a foetus if a pregnant woman is infected.
After infection, Toxoplasma moves to parts of the brain involved in emotion and behaviour. Changes in these areas have been seen in suicide victims.
Prof Brundin said: “Suicide is a major health problem. I think it’s very positive that we are finding biological changes in suicidal patients.
“It means we can develop new treatments to prevent suicides, and patients can feel hope that maybe we can help them.”
Previous research has suggested that 10-20 per cent of the UK population have been infected with Toxoplasma.
Scottish scientists are studying people in Glasgow and Dundee to determine the extent of infection north of the Border.
A study by the Moredun Research Institute found more than half of Scottish sheep have had Toxoplasma, suggesting it is widespread in the environment.
Dr Frank Katzer, who works at Moredun, recommended that to avoid infection people should wash fruit and vegetables, cook meat well and wash hands after handling cat litter.
However, he was not convinced Toxoplasma posed a large suicide risk.
He said: “There is conclusive evidence from controlled animal studies that infected mice exhibit altered behaviour.
“Many people have tried to link Toxoplasma with neurological disorders. However, it is challenging to study real people in real environments as there are many uncontrolled factors.
“It is possible there could be some influence on human behaviour, but I’m not sure how significant that would be.”
Prof Brundin agreed the majority of those infected will not attempt suicide but added: “Some individuals may for some reason be more susceptible to develop symptoms.”