How a Common Parasite Causes Personality Change

May 7, 2020

Scientists are learning more about how the brain reacts to infection. What may cause devastating effects in one person, may be relatively harmless in another.

orty million Americans are infected with a parasite called Toxoplasma gondii. For most patients, the infection is mild, while others develop seizures or psychiatric disorders. New research by scientists at the Fralin Biomedical Research Institute at VTC describes how brain circuits change as the parasite finds long-term shelter inside brain cells.
Credit Michael Fox Lab/Virginia Tech

According to the centers for disease control, some 40 million people in the U.S. are infected with  a toxin that causesToxoplasmosis and most don’t even know they have it.  

“One of the interesting things about this parasite is that it seems to prefer to hide in neurons of the brain."  Dr. Michael Fox directs the center for neurobiology at Virginia Tech's  Fralin Biomedical Research Institute.   “We think that one of the reasons this is the case is, these cells don’t produce the sort of immune molecules which could trigger an immune response. In essence, this parasite can hide in the neurons and be kind of hidden away from the immune system.”


  Toxoplasmosis is most often associated with cats. That’s why pregnant women are instructed not to clean the litter box.  Mice can get infected with toxin, causing behavioral changes."One hallmark symptom in infected mice is their tendency to approach known predators, such as cats, displaying a lack of fear, survival instincts, or situational processing." according to the study's authors.  This makes it easier for cats to prey on them.

The parasite can also come from under cooked meat. For most people who consume it, it causes mild to moderate flu like symptoms but in some people, it can also  alter personality, cause mood disorder, vision changes, even seizures.

A graduate student in Fox’s lab, Gabrielle Carrillo, made the discovery as to how the toxin destroys synapses in some people, essentially re-wiring the brain, causing dramatic personality change.

The study was published last month in the journal, Glia.