The Toxoplasma parasite can be deadly, causing spontaneous abortion in pregnant women or killing immune-compromised patients, but it has even stranger effects in mice.
A mouse infected with the Toxoplasma parasite loses its fear of cats, which is good for both the parasite and the cat. The cat gets an easy meal, while the parasite gets into the cat's intestinal system, the only place it can sexually reproduce and complete its cycle of infection.
Credit: Wendy Ingram, UC Berkeley
Infected mice lose their fear of cats, which is good for both cats and the parasite, because the cat gets an easy meal and the parasite gets into the cat's intestinal track, the only place it can sexually reproduce and continue its cycle of infection.
New research by graduate student Wendy Ingram at the University of California, Berkeley, reveals a scary twist to this scenario: the parasite's effect seem to be permanent. The fearless behavior in mice persists long after the mouse recovers from the flu-like symptoms of toxoplasmosis, and for months after the parasitic infection is cleared from the body, according to research published today (Sept. 18) in the journal PLOS ONE.
"Even when the parasite is cleared and it's no longer in the brains of the animals, some kind of permanent long-term behavior change has occurred, even though we don't know what the actual mechanism is," Ingram said. She speculated that the parasite could damage the smell center of the brain so that the odor of cat urine can't be detected. The parasite could also directly alter neurons involved in memory and learning, or it could trigger a damaging host response, as in many human autoimmune diseases.
Ingram became interested in the protozoan parasite, Toxoplasma gondii, after reading about its behavior-altering effects in mice and rats and possible implications for its common host, the domesticated cat, and even humans. One-third of people around the world have been infected with Toxoplasma and probably have dormant cysts in their brains. Kept in check by the body's immune system, these cysts sometimes revive in immune-compromised people, leading to death, and some preliminary studies suggest that chronic infection may be linked to schizophrenia or suicidal behavior.
Pregnant women are already warned to steer clear of kitty litter, since the parasite is passed through cat feces and can cause blindness or death in the fetus. One main source of spread is undercooked pork, Ingram said.
With the help of Michael Eisen and Ellen Robey, UC Berkeley professors of molecular and cell biology, Ingram set out three years ago to discover how Toxoplasma affects mice's hard-wired fear of cats. She tested mice by seeing whether they avoided bobcat urine, which is normal behavior, versus rabbit urine, to which mice don't react. While earlier studies showed that mice lose their fear of bobcat urine for a few weeks after infection, Ingram showed that the three most common strains of Toxoplasma gondii make mice less fearful of cats for at least four months.
Using a genetically altered strain of Toxoplasma that is not able to form cysts and thus is unable to cause chronic infections in the brain, she demonstrated that the effect persisted for four months even after the mice completely cleared the microbe from their bodies. She is now looking at how the mouse immune system attacks the parasite to see whether the host's response to the infection is the culprit.
"This would seem to refute – or at least make less likely – models in which the behavior effects are the result of direct physical action of parasites on specific parts of the brain," Eisen wrote in a blog post about the research.
"The idea that this parasite knows more about our brains than we do, and has the ability to exert desired change in complicated rodent behavior, is absolutely fascinating," Ingram said. "Toxoplasma has done a phenomenal job of figuring out mammalian brains in order to enhance its transmission through a complicated life cycle."
Robert Sanders | EurekAlert!
The big clean up after stress
25.05.2018 | Julius-Maximilians-Universität Würzburg
Complementing conventional antibiotics
24.05.2018 | Goethe-Universität Frankfurt am Main
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
24.05.2018 | Ecology, The Environment and Conservation
24.05.2018 | Medical Engineering
24.05.2018 | Physics and Astronomy