Women who carry a common parasite may be more likely to harm themselves or attempt suicide, according to new research at the University of Maryland School of Medicine in Baltimore.
The infection, called toxoplasmosis, is caused by the parasite Toxoplasma gondii.
People can become chronically infected by eating undercooked meat or unwashed vegetables or by handling cat litter — the parasite is known to thrive in the gut of infected cats.
Often the disease has no symptoms, but it can be dangerous to those with a weak immune system or during pregnancy — the parasite can be passed on to babies.
Research has also linked the parasite to a higher chance of developing schizophrenia, and researchers believe that since the T. gondii parasite resides in the brain, it could have an effect on emotions and behavior.
For the new study, Dr. Teodor Postolache from the University of Maryland School of Medicine in Baltimore and his colleagues used Danish medical registries to assess 45,788 women who were originally included in a study that screened infants for toxoplasmosis.
Just over one-fourth of the babies tested positive for T. gondii antibodies, meaning their mothers probably had a chronic, underlying toxoplasmosis infection.
Over the next 11 to 14 years, infected women were about 50 percent more likely to cut, burn or otherwise harm themselves, according to their medical records, and 80 percent more likely to attempt suicide.
Overall, 488 women hurt themselves for the first time during the study (eight out of every 10,000 annually) and 78 tried to kill themselves.
“That’s not a very high risk, when you come down to it,” said Dr. Louis Weiss, who studies toxoplasmosis at Albert Einstein College of Medicine in New York.
Still, he told Reuters Health the findings are “really quite interesting.” Part of the study’s strength, he added, comes from how large it was and how long it followed the women.
“There probably is an effect of this parasite on human behavior, which has been suspected,” based on studies of animals infected with toxoplasmosis, said Weiss, who wasn’t involved in the new research.
Eighteen women in the study committed suicide, which was too small a number for the researchers to determine whether T. gondii put some women at higher risk.
Postolache and his colleagues note that some of the self-harm incidents might not have shown up in their records if the women hadn’t been taken to a mental health clinic.
Based on the research, it is hard to say for sure whether the parasite caused women to hurt themselves or attempt suicide. It could be, for example, that women with underlying mental problems were more likely to get toxoplasmosis because they cooked their meat or washed their vegetables improperly.
But it’s reasonable, Postolache added, that the parasite could directly affect the brain, such as by making cells produce more or less of certain neurotransmitters that control mood and behavior.
“It’s (also) possible that the immune system containing Toxoplasma gondii does it at the cost of affecting brain function,” he said.
The chronic infection could trigger inflammation, Weiss explained, which might subtly change brain chemistry.
Postolache said more research is needed to really understand the link between toxoplasmosis and suicidal tendencies, such as whether certain individuals with the infection are more susceptible to mood and behavior issues than others – because of genetic factors, for example.
The researchers added that pregnant women should not avoid or give away their housecats based on the findings. Most of the parasites that cause infection, Weiss said, are passed by feral cats and end up in the environment.
“This is not a reason to be fearful of pussy cats,” he said.
The findings are published in the Archives of General Psychiatry.