Posts Tagged “ toxoplasmosis ”

Written by Gabriela Segura, MD
Sunday, 8 April 2012 05:30

Toxo keeps popping up again and again on behavioral and neurological research. I talked about it awhile ago in Toxoplasmosis and Personality Changes,  but a friend brought to my attention the following paper:

Infect Genet Evol. 2012 Mar;12(2):496-8. Epub 2012 Jan 25.

Brain cancer mortality rates increase with Toxoplasma gondii seroprevalence in France.


IRD, MIVEGEC (UMR CNRS/IRD/UM1), 911 Ave. Agropolis, BP 64501, FR-34394 Montpellier Cedex 5, France; Centre de Recherche de la Tour du Valat, Le Sambuc, 13200 Arles, France.


The incidence of adult brain cancer was previously shown to be higher in countries where the parasite Toxoplasma gondii is common, suggesting that this brain protozoan could potentially increase the risk of tumor formation. Using countries as replicates has, however, several potential confounding factors, particularly because detection rates vary with country wealth. Using an independent dataset entirely within France, we further establish the significance of the association between T. gondii and brain cancer and find additional demographic resolution. In adult age classes 55years and older, regional mortality rates due to brain cancer correlated positively with the local seroprevalence of T. gondii. This effect was particularly strong for men. While this novel evidence of a significant statistical association between T. gondii infection and brain cancer does not demonstrate causation, these results suggest that investigations at the scale of the individual are merited.

Copyright © 2012 Elsevier B.V. All rights reserved.

There is still more research to be done, as it is usually said “correlation does not imply causation”. But toxoplasma gondii is turning out to be much more problematical than people will like to admit. In fact, I stumbled upon an interesting remark on the paper:

Latent T.gondii infections are traditionally considered benign by conventional medicine, but evidence is accumulating that the bradyzoite stages encysted in the brain during the latent phase are responsible for diverse neurological pathologies (see Flegr,2010 for a recent review). T.gondii is sufficiently common in humans that it could lead to a large proportion of brain cancer cases (Thomasetal.,2012).”

Toxoplasma gondii is the most common protozoan parasite in developed nations and up to 80% of the population may be infected, depending on eating habits and exposure to cats. After the initial acute infection, the latent and dormant form of T. gondii is found predominantly in nervous and muscle tissues in infected people. Until recently, latent infections in humans were assumed to be asymptomatic but personality profiles, behavior, and psychomotor performance tells a different story. The evidence accumulating is indeed a bit frightening.

The life cycle of Toxoplasma, © Marcia Hartsock

Take for instance this study: Read more…

Written by Gabriela Segura, MD
Tuesday, 17 March 2009 13:10

Toxoplasma gondii is a parasite that lives in the intestines of cats, shedding eggs that can be picked up by rats and other animals. Humans and other animals can be hosts to Toxoplasma as well. People get infected by its eggs by handling soil or kitty litter. It is thought that for most people the parasite lives “quietly” in their bodies including the brain, and about half of the world’s population is infected. Toxoplasmosis is only an immediate threat for people with low defenses (i.e. AIDS, pregnancy).

In general, healthy rats get anxious with the odor of cat urine and they shy away from it, making them more cautious. But scientists at Oxford discovered that Toxoplasma changes this self-preserving mechanism in rats, making them more likely to get themselves killed. The scent of a cat didn’t make them anxious or cautious. Instead, they even took a special interest in the odor and came back to it repeatedly.

The scientists speculated that Toxoplasma was capable of secreting a substance that was altering the patterns of brain activity in the rats. Given the similarity between the basic anatomy and brain chemical activity between rats and humans, the question then became if toxoplasmosis could alter human behavior as it did with our formerly cautious rats. Furthermore, a link between schizophrenia and toxoplasmosis has been made which was confirmed with recent research where it was proven that toxoplasmosis changes some of the chemical messages in the brain. These chemical changes can have an enormous effect on human behavior. The parasite infects the brain producing an enzyme called tyrosine hydroxylase, which is needed to make dopamine. Dopamine’s role in mood, sociability, attention, motivation and sleep patterns are well documented, and it also has an important role in schizophrenia:

Read more…