07 December 2012

Research Into How Common Cat Parasite, Toxoplasma gondii, Enters The Human Brain

Researchers have discovered how the common cat parasite, Toxoplasma gondii, enters the human brain and affect the hosts behavior.

Toxoplasmosis is one of the most prevalent parasitic infections in the world. It is estimated that thirty to fifty percent of the world's population is infected.

In the US, it is estimated that sixty million have toxoplasmosis.

Toxoplasmosis is caused by the parasite, Toxoplasma gondii. It is passed on through humans mostly through cats but can also be transmitted through raw uncooked meat and vegetables harboring the parasite or through contaminated water.

Few manifest symptoms of Toxoplasmosis because of the immune system that keeps it at bay. People with weak or compromised immune systems as well as pregnant women are at risk of acquiring it. In the case of pregnant women, they can also infect their unborn child with the parasite.

In some instances, individuals with healthy immune systems may suffer eye damage from the disease.

Sever cases of toxoplasmosis can cause damage to the brain, eyes, and other organs. It may also lead to mental illness, such as schizophrenia and behavioral changes. A recent study links toxoplasmosis to suicidal tendencies among women.

The CDC considers toxoplasmosis as one of the Neglected Parasitic Infections, a group of five parasitic diseases that have been targeted by CDC for public health action.

New research investigates how the common 'cat parasite' gets into the brain

A new study demonstrates for the first time how the Toxoplasma gondii parasite enters the brain to influence its host's behavior. This research was led by researchers from the Karolinska Institute and Uppsala University in Sweden publishes today in the Open Access journal PLOS Pathogens.

The Toxoplasma gondii parasite causes toxoplasmosis. The parasite is common and infects between 30 and 50 per cent of the global population. It also infects animals, especially domestic cats. Human infection is contracted by eating poorly cooked (infected) meat and handling cat feces. Toxoplasmosis first appears with mild flu-like symptoms in adults and otherwise healthy people before entering a chronic and dormant phase, which has previously been regarded as symptom-free. But when the immune system is weakened toxoplasmosis in the brain can be fatal. The fetus can be infected through the mother and because of this risk, pregnant women are recommended to avoid contact with cat litter boxes. Surprisingly, several studies in humans and mice have suggested that even in the dormant phase, the parasite can influence increasing risk taking and infected people show higher incidence of schizophrenia, anxiety and depression, which are broader public health concerns.

Video: Toxoplasmosis

In their recent study Fuks et al. showed for the first time how the parasite enters the brain and increases the release of a neurotransmitter called GABA (gaba-Aminobutyric acid), that, amongst other effects, inhibits the sensation of fear and anxiety. In one laboratory experiment, human dendritic cells were infected with toxoplasma. After infection, the cells, which are a key component of the immune defense, began actively releasing GABA), In another experiment on live mice, the team was able to trace the movement of infected dendritic cells in the body after introducing the parasite into the brain, from where it spread and continued to affect the GABA system.

"For toxoplasma to make cells in the immune defense secrete GABA was as surprising as it was unexpected, and is very clever of the parasite," says Antonio Barragan, researcher at the Center for Infectious Medicine at Karolinska Institute and the Swedish Institute for Communicable Disease Control. "It would now be worth studying the links that exist between toxoplasmosis, the GABA systems and major public health threats."


Public Library of Science
PLOS Pathogens
Karolinska Institute
Uppsala University
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