Common Parasite Of Cat Litter May Increase Suicide Risk In Women
July 3, 2012

Common Parasite Of Cat Litter May Increase Suicide Risk In Women

Lawrence LeBlond for - Your Universe Online

What do unwashed vegetables, undercooked meat, and dirty kitty litter all have in common? For one, they are all known to likely harbor a nasty parasite, which in a recent study has been linked as a killer among women who come into contact with the common critter.

To be more specific, the parasite -- Toxoplasma gondii -- has been linked with an increased risk of mental health problems and attempted suicide in women who become infected.

Scientists have long known that the parasite could increase the risk of stillbirth or brain damage of the unborn if pregnant women become infected, and urge them not to change or be near cat litter while pregnant.

But in the new study, published today in the journal Archives of General Psychiatry, scientists from the University of Maryland School of Medicine followed more than 45,000 Danish women who had been infected with the parasite and also had children for more than a decade and found those with the infectious parasite were one and a half times more likely to attempt suicide than those not infected.

The researchers found that, as the level of antibodies in the blood rose, so did the suicide risk. The relevant risk was even higher for violent suicide attempts they found. While the researchers found that 81 percent of infected women are more likely to attempt violent suicide than other ways, the actual risk overall is relatively small.

“We can´t say with certainty that T. gondii caused the women to try to kill themselves, but we did find a predictive association between the infection and suicide attempts later in life that warrants additional studies. We plan to continue our research into this possible connection,” said Dr. Teodor T. Postolache, MD, associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine.

“There is a good possibility that there is some causal link here,” he told WebMD℠s Salynn Boyles.

Nearly a third of the world´s population is infected with T. gondii, which hides in cells in the brain and muscles, and often goes undetected because it generally does not cause problems. But when it does cause a problem, the infection, known as toxoplasmosis, has been linked to a number of mental illnesses, such as schizophrenia. It has also been linked with fetal brain damage, blindness, and severe mental retardation when the parasite is transmitted from women to their unborn fetuses.

“T. gondii infection is a major public health problem around the world, and many people don't realize they're infected,” said E. Albert Reece, PhD, MBA, vice president of medical affairs at the University of Maryland School of Medicine.

“Dr. Postolache is a leading expert on suicide neuroimmunology. Suicide is a critically important mental health issue. About 1 million people commit suicide and another 10 million attempt suicide worldwide each year. We hope that this type of research will one day help us find ways to save many lives that now end prematurely in suicide,” he said.

This was the largest study of T. gondii and attempted suicide and the first prospective study to document suicide attempts that occurred after the infection was discovered. Postolache´s research team was also the first to report a connection between the parasite and suicidal behavior in 2009. In the latest study, Postolache is collaborating with researchers from Denmark, Germany and Sweden to confirm the mechanism responsible for this association.

Suicide is a global health problem with an estimated 10 million suicide attempts every year, as many as a million being successful, according to Postolache´s research. More than 60 million men, women and children in the US carry the parasite, according to the US Centers for Disease Control and Prevention (CDC), but very few have symptoms.

The parasite thrives in the intestines of cats, and spreads through oocysts passed in their feces. All warm-blooded animals can become infected through ingestion of these oocysts.

A 2011 study on rats infected with the parasite showed that their fear of cats disappeared. Instead, the areas of the brain associated with sexual arousal were activated. Researchers theorized that the mind-manipulating T. gondii ensures that the parasite will reach and reproduce in the gut of a cat, which it depends upon for its survival.

“The parasite does actually alter the brain of its host,” Stanford University study co-author Patrick House told in an interview after the publication of last year℠s rat study. “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.”

The 2011 study, along with other previous research on T. gondii is what led Postolache to investigate the relationship between the parasite and biological changes in the human brain that might lead to suicide.

“I was interested in the neuron aspects of suicide and intrigued by low-grade activation in patients who attempted suicide, as well as victims,” Postolache explained. “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?”

For the study, Postolache and colleagues analyzed data from women who had given 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. They then cross-checked the death registry to see if these women later killed themselves. They also used psychiatric records to rule out women who had prior history of mental illness.

Postolache noted that the study did have limitations, such as the inability to determine the cause of suicidal behavior. “T. gondii infection is likely not a random event and it is conceivable that the results could be alternatively explained by people with psychiatric disturbances having a higher risk of becoming T. gondii infected prior to contact with the health system,” he added.

In a prepared statement, J John Mann, MD, of Columbia University Medical Center, said Postolache´s work emulates his own 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.”

He added that a better understanding of how infections like T. gondii may trigger self-harm responses in people who are already depressed could lead to “new ways of thinking of risk, prevention, and risk reduction for suicide.”

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, Mann noted.

And research also shows that streptococcus bacteria can trigger obsessive-compulsive disorder  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.

Postolache suspects that some people are predisposed 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.

He warns, however, that even if a direct cause were found, no antibiotics yet exist and it could be years before an effective vaccine or other treatment may be developed to stop the neurological damage produced by toxoplasmosis.

Currently, the most effective weapon against T. gondii is education about hand washing, proper cooking of meats, and keeping food prep areas properly sanitized. And letting your cats roam free on sideboards and food prep stations only raises the risk for infection, said Postolache.