Is Your Cat Hosting a Human Suicide Parasite?

new study of more than 45,000 women, the largest of its kind, suggests that there could be a link between infection with the Toxoplasma gondii (T. gondii) parasite and suicides among women. T. gondii is sometimes called the “Kitty Litter Parasite” because it usually spreads through contact with cat feces. (correction: it should also be mentioned that in the United States, T. gondii is also transmitted via contact with uncooked contaminated meat and vegetables; contact with cat feces is certainly not the only means of transmission in the US or abroad).

About one third of the world’s population is infected with the parasite, which stealthily hides from the human immune system in brain and muscle cells. Often the host will not develop symptoms of the infection (called toxoplasmosis), but a fair amount of research evidence suggests that it is linked to subsequent mental illness, including schizophrenia and bipolar disorder, and also increased risk of traffic accidents.

The latest research is the first to link T. gondii with suicides across a large human population. Quoting senior author of the research paper and leading expert on suicide neuroimmunology, Tedor T. Postolache, M.D., "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.”

Researchers analyzed data from 45,788 women in Denmark, who gave birth between May 15, 1992 and Jan. 15, 1995 and whose babies were screened for T. gondii immunoglobulin antibodies. Babies don't produce antibodies to T. gondii for three months after they are born, so the antibodies present in their blood represented infection in the mothers.

The research team searched Danish health registries to determine if any of these women later attempted suicide, including cases of violent suicide attempts which may have involved guns, sharp instruments and jumping from high places. The researchers also cross-checked records in the Danish Psychiatric Central Register to determine if the women had been diagnosed previously with mental illness.

The study found that women infected with T. gondii were one and a half times more likely to attempt suicide compared to those who were not infected, and the risk seemed to rise with increasing levels of the T. gondii antibodies.  The suicides linked to these high levels of infection were also the most violent. Evidence of previous mental illness did not significantly change the findings.

T. gondii has also been linked to suicides, of a sort, among our friends the rodents. Previous research showed that infected rats experience a reduced fear response to cat odors, making them more likely to come sniffing around your feline’s territory. When a cat eats the rodent, it ingests the parasite, which then finds a comfortable place to hang out in the cat’s intestines.

The latest study has a few limitations, not the least of which is an inability to determine a specific cause for the 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," Dr. Postolache says.

At the least, the findings should support the need for future research to determine whether the parasites our cats are hosting would like to drive our brains off the highway.

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Posted on September 15, 2012 .