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I'm crazy...not my fault, not guilty (Toxoplasmosis)

February/March 2015

Editor’s note: This lighthearted article about Toxoplasmosis was written by Canadian researcher, Virginie Barrere. Toxoplasma originates in cats and is spread through their faeces. It can affect sheep and can cause abortions and lamb deaths (click here for sheep information). However, the parasite is of more concern as a human health risk, though in Australia there are relatively few cases each year. Pregnant women are advised to avoid handling cat faeces (e.g. cleaning the litter box) and raw meat.


by Virginie Barrere, Parasitologist, Canada

Seeing my face that morning, my doctor decided to prescribe me a blood test. “While we’re doing this”, he said, “We’ll look for Toxo. When I read the blood test results, I discovered I was Toxo positive: it meant that I had been infected with this parasite before. My doctor told me that this information will be useful someday when I would be willing to be pregnant. At that time he did not mention, " … and you may experience suicidal tendencies, depression, schizophrenia and aggressiveness! "

Some explanation:

Toxoplasma gondii or Toxo, is a protozoan parasite like Plasmodium, which causes malaria, or like Trypanosoma, which causes sleeping sickness. Contamination is via:

  • Consumption of undercooked meat contaminated with the parasite
  • Consumption of vegetables contaminated with the parasite if they are not sufficiently rinsed, or finally
  • Cats that carry the parasite. Faeces may contain the parasite and as a result it is possible to get infected while changing the litter.

Toxoplasma infection can go unnoticed because it is similar to flu symptoms and presents, at first, no danger to the host. However, be aware that it can be dangerous for people with depressed immune systems, pregnant women and their unborn child. Within its host, the protozoan forms cysts in the muscles including the brain. For many years, scientists thought that these cysts did not represent any danger. However, further to observations made on rodents infected with Toxo, researchers have begun to pay more attention to the behaviours of human hosts. Indeed, it seemed that Toxo infected rodents had less fear of cats and were also more adventurous.

What happens when humans get infected with Toxo?

The researcher Dr. Adam Markowitz and his team in United States have established a link between Toxoplasma infection and anxiety in infected individuals. Similarly, the team of Dr. Thomas Cook correlated our little parasite and aggressive trait among women and impulsive trait in men under the age of 60. And what about the scientific Dr. Jaroslav Flegr (Czech Republic) who works on the relationship between host behavioural disorders and Toxoplasma? He argues that the protozoan causes schizophrenic behaviours among hosts who would also have longer reaction times and are more likely to have traffic accidents.

One third of the world population is concerned

But why would this parasite make us experience this? This could be explained by the positioning of Toxo cysts in the brain. In fact, according to a scientific team in Germany led by Dr. Haroon, these cysts persist in limbic regions known to modulate anxiety. Another explanation would be Toxoplasma life cycle. The protozoan must be ingested by a cat to complete its life cycle. This would explain why infected rodents have less fear of cats and their smell.

It seems that the parasite forced his host to get eaten by a cat in order to continue its life. For a human perspective, does the parasite do the same thing by making us more suicidal, schizophrenic or impulsive or on a lighter note, in love with cats? According to a study made in 2004, one third of the world population would be Toxo positive; this represents a significant number of potential schizophrenics, impulsive or aggressive people and dangerous drivers to make a point. Many scientists are working on this issue over the world and will provide more precise answers to these questions.


See more articles on Toxoplasma:

FUNNY: Parasite makes men dumb, women sexy (Sydney Morning Herald)

IN DEPTH: Toxoplasma gondii (Foodstandards Australia New Zealand)

LIGHT: What is Toxoplasmosis? (RSPCA Australia)