July 9 Women who are infected with a common
parasite may be more likely to harm themselves or to attempt
suicide, according to a study of more than 45,000 Danish women.
The infection, known as toxoplasmosis, is caused by the
parasite Toxoplasma gondii. Humans can become chronically
infected by eating undercooked meat or unwashed vegetables, or
by handling cat litter, as the parasite is known to multiply in
the gut of infected cats.
Some studies have linked the parasite to a higher chance of
developing schizophrenia, and researchers believe that because
the T. gondii parasite lives in the brain, it could have an
effect on emotions and behavior.
"Women with a T gondii infection have an increased risk of
self-directed violence," wrote study leader Teodor Postolache at
the University of Maryland School of Medicine in Baltimore in
the Archives of General Psychiatry.
For the study, Postolache and his colleagues used Danish
medical registries to track 45,788 women who were originally
included in a study that screened newborn babies for
Toxoplasmosis is often symptom-free, but it can be dangerous
in people with weak immune systems or during pregnancy, since
the parasite may be passed to babies.
All of the infants in the screening were tested for
antibodies against the parasite through a blood sample drawn
five to 10 days after birth. Because the babies were still too
young to make their own antibodies, any that showed up in their
blood would have been passed from their mothers.
Just over one-quarter of the babies were positive for the
antibodies, meaning their mothers likely had a chronic,
underlying toxoplasmosis infection.
And over the next 11 to 14 years, infected women were about
50 percent more likely to cut, burn or otherwise hurt
themselves, according to their medical records. They were 80
percent more likely to attempt suicide.
In total, 488 women hurt themselves for the first time
during the study, or eight out of every 10,000 annually, and 78
tried to kill themselves.
Louis Weiss, who studies toxoplasmosis at Albert Einstein
College of Medicine in New York but was not involved with the
study, said the findings were "really quite interesting" but
that the risk was not very high.
"There probably is an effect of this parasite on human
behavior, which has been suspected" based on studies of animals
infected with the parasite, Weiss added.
Overall, only 18 women in the study actually committed
suicide, which was too small a number for the researchers to
determine if the parasite put some women at higher risk.
Based on the studies, Postolache and his colleagues also
could not say for sure whether toxoplasmosis infection caused
the women to harm themselves or attempt suicide. It could be,
for example, that women with underlying mental problems were
more likely to pick up the parasite because they cooked their
meat or washed their vegetables improperly.
But he also said the parasite could directly affect the
brain, by making cells produce more or less of certain
neurotransmitters that control mood and behavior. The immune
system may also contain an infection at the cost of brain
Both researchers emphasized that pregnant women should not
avoid or get rid of their housecats based on the findings, with
Weiss noting that most of the parasites that cause infection are
passed by feral cats and end up in the environment.
(Reporting from New York by Genevra Pittman at Reuters Health,
editing by Elaine Lies)