According to a recent international study conducted by the University of Maryland School of Medicine, a common parasite that can lurk in cat litter boxes may cause undetected brain changes in women that make them more prone to suicide.
Scientists have long known that pregnant women infected with the toxoplasma gondii parasite — spread through cat feces, undercooked meat or unwashed vegetables — could risk still birth or brain damage if transmitted to an unborn infant.
But this new study of more than 45,000 women in Denmark shows changes in their own brains after being infected by the common parasite.
When infected with T. gondii women were one and a half times more likely to attempt suicide than those who were not infected. As the level of antibodies in the blood rose, so did the suicide risk with the relative risk for violent suicide attempts even higher.
It can’t be said with certainty T. gondii was the reason these women to tried to kill themselves, but the study did find a predictive association between the infection and suicide attempts later in life. These findings are certainly enough to warrant additional studies with a larger cohort for a better understanding of the vulnerabilities that certain people have to the parasite.
Suicide is a global public health problem so anything with the potential to increase risk of suicide is a serious problem that needs to be addressed. According to researchers that conducted the study an estimated 10 million attempt suicide and 1 million are successful.
A number that is even more alarming is about one-third of the world is exposed to T. gondii, and most never experience symptoms and therefore don’t know they have been infected. When humans ingest the parasite, the organism spreads from the intestine to the muscles and the brain.
According to the Centers for Disease Control and Prevention, there are more than 60 million men, women, and children in the United States alone that carry the toxoplasma parasite, but very few have symptoms.
Toxoplasmosis is considered one of the “neglected parasitic infections,” a group of five parasitic diseases that have been targeted by CDC for public health action.
Previous research on rodents shows that the parasite can reside in multiple brain structures, including the amygdala and the prefrontal cortex, which are responsible for emotional and behavioral regulation.
“The parasite does actually alter the brain of its host,” Stanford University study co-author Patrick House told ABCNews.com last year. “The fact that a parasite can get into an organism, target its brain, stay there without killing the host and alter the circuitry of the brain — we’ve seen this is insects and fungi, but it’s the first time we’ve seen it in a mammalian host.”
It was this and other research that led University of Maryland School of Medicine psychiatrist and suicide neuroimmunology expert Dr. Teodor T. Postolache, to investigate the relationship between the parasite and biological changes in the brain that might lead to suicide. He was also intrigued by studies on allergies and research that showed a connection between toxoplasmosis and schizophrenia.
“I was interested in the neuron aspects of suicide and intrigued by low-grade activation in patients who attempted suicide, as well as victims,” he said. “Other studies had looked at the brain and suicide risk and impulsivity. The next question was, what could be the triggers that perpetuate this level of heightened activation in the brain?”
Postolache collaborated with Danish, German and Swedish researchers, using the Danish Cause of Death Register, which logs the causes of all deaths, including suicide. The Danish National Hospital Register was also a source of medical histories on those subjects.
They analyzed data from women who gave birth between 1992 and 1995 and whose babies were screened for T. gondii antibodies. It takes three months for antibodies to develop in babies, so when they were present, it meant their mothers had been infected. Scientists then cross-checked the death registry to see if these women later killed themselves. They used psychiatric records to rule out women with histories of mental illness.
Dr. J. John Mann, a psychiatrist from Columbia University, said Postolache’s research mirrors his work in the field of suicidal behavior. ”The relationship of the brain to the immune system is more complex than it may appear,” said Mann. “The brain regulates the stress response system, which impacts the immune response.”
Scientists already know that steroids like cortisone can affect the immune response. Some antibodies whose goal is to kill off cancer can also affect the brain. Oftentimes the first symptom of pancreatic cancer is depression, he said.
Research also shows that streptococcus bacteria can trigger obsessive-compulsive disorder (OCD) in some children. Sydenham’s chorea, the loss of motor control that can occur after acute rheumatic fever, may also be an immune response affecting the brain, according to Mann.
Maryland researcher Postolache suspects that some individuals have a predisposition to these neurological changes. He speculates that the parasite may disrupt neurological pathways in those who are vulnerable, so that projections of fear and depression from the amygdala are not tempered or controlled by the “braking” function of the prefrontal cortex.
Even if a direct cause were found, no antibiotics for T. gondii yet exist and it could be a decade before effective vaccines or other agents that might stop the neurological damage are developed.
Right now, the most effective weapon against T. gondii is education about handwashing, the proper cooking of food, and not using a knife exposed to raw meat on cooked meat.