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Cat Ladies at Higher Risk for Suicide? (Part 1)

A recent study published by the University of Maryland School of Medicine found that negative personality changes and mental illness in humans may result from exposure to a parasite that exists in almost every cat's litter box, no matter how fastidious the owner may be.

Toxoplasma gondii, also known as T.gondii or Toxo may be the source of changes in the human brain that result in strange behavior or even suicide. In fact, researchers found that women who own cats are more likely to suffer from mental-health issues and are one-and-a-half times more likely to attempt suicide than uninfected women.

Owning or caring for higher numbers of cats may increase the level of T.gondii antibodies, and the higher the levels of T. gondii antibodies found in women who were infected, the higher the suicide risk, according to the report.

Up to now it has been commonly accepted that pregnant women and anyone with a suppressed immune system should not be exposed to cat feces, but there has been little explanation in non-scientific circles to help us really understand why or how it affects humans and unborn children. These major concerns are presented by Rick Gerhold, DVM, PhD, and associate at the Center for Wildlife Health at the University of Tennessee in a 2011 article entitled, Cats as Carriers of Disease.

Dr. Gerhold explains, “Contact with infective T.gondii oocysts in cat feces is found to be a primary risk factor for toxoplasmosis in humans, who become infected primarily by ingestion of sporulated oocysts from contaminated soil or water or by ingesting tissue cysts in undercooked or raw meat. Since cats are the only definitive host that sheds oocysts [which are like a microscopic egg, with a tough shell], these types of outbreaks have to be cat-feces associated.”

The T. gondii parasite thrives and reproduces in the intestines of cats. Humans and any warm-blooded animals can become infected through ingestion of these oocysts. The organism spreads to their brain and muscles, hiding from the immune system within “cysts” inside cells.

Humans can become infected by changing their infected cats’ litter boxes, eating unwashed vegetables, drinking water from a contaminated source, or more commonly, by eating undercooked or raw meat that is infested with these cysts--which originate only in cat feces.

Dr. Gerhold describes that the T.gondii infection can cause neurological impairment and lead to abortions and birth defects in humans and is a major cause of systemic infection and death for immunouppresed patients.

During acute toxoplasmosis, symptoms are often influenza-like: swollen lymph nodes or muscle aches and pains that last for a month or more. Rarely, a patient with a fully functioning immune system may develop eye damage from toxoplasmosis, medical experts advise.

Young children and immunocompromised patients, such as those with HIV/AIDS, those taking certain types of chemotherapy or those who have recently received an organ transplant may develop severe toxoplasmosis. This can cause damage to the brain (encephalitis) or the eyes

In regard to mental and neurological damage, Dr. Gerhold writes that Toxoplasmosis has been associated with increased risk of schizophrenia, autism disorders, and other neuro-inflammatory diseases.

He stresses that one study found that the prevalence of T.gondii is higher in feral cats than in pet cats but that the oocysts are extremely environmentally resistant and infections can occur months or even years after excretion of the parasite. This is the reason that any garden area, children’s sandboxes or other outdoor recreational areas can be a source of infection for humans.

A 2012 study of 45,000 women in Denmark has now shown even more dire consequences of exposure to Toxoplasma. A team of researchers led by Dr. Teodor T. Postolache, an associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland, has now determined that women who were infected with T. gondii were one-and-a-half times more likely to attempt suicide than uninfected women. The higher the levels of T.gondii antibodies found in women who were infected, the higher the suicide risk. They were also more likely to try to commit suicide violently, with a gun, sharp object or by jumping.

The researchers state that they couldn’t establish that T.gondii infection actually causes increased risk of suicide, only that it was associated. And they make it clear they are not sure exactly why the link exists. “Is the suicide attempt a direct effect of the parasite on the function of the brain or an exaggerated immune response induced by the parasite affecting the brain? We do not know.”

The authors call for further studies focusing on the biological mechanisms of the parasite and how it may affect people’s suicide risk and other personality factors. Senior study author Postolache said: "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."


Gerhold, R. 2011. Cats as carriers of disease: the potential to spread a host of diseases to humans and wildlife. Wildlife Professional.


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