FRIDAY, Dec. 14, 2012 — It's the stuff of science fiction: A creepy microscopic organism worms its way into the human brain, stays quietly under the radar, and then startles the brain's neurotransmitters to the point of no return.
Medical researchers have long known about toxoplasma gondii, the brain-loving parasite that's most commonly associated with gentle feline creatures. "It's often referred to as the 'cat poop parasite,'" says Jessica Weidner, a postdoctoral fellow at Wenner-Gren Foundation, a nonprofit supporting anthropology research in New York City, and coauthor of a new study that investigates how toxoplasma enters the brain.
Though many researchers say there's mixed evidence, the parasite has been linked to a number of psychiatric conditions, including schizophrenia, anxiety, and depression. It's known to be harmful to pregnant women since a fetus can potentially become infected through its mother, which is why pregnant women have long been cautioned to stay away from the cat litter box.
"One thing that should be known is the parasite has been living within immune systems for many millenniums," says Weidner, whose study was just published in PLOS Pathogens. It's estimated that somewhere between 30 percent to 50 percent of people worldwide are infected with this parasite.
For their study, Weidner and her team at the Karolinska Institute and Uppsala University in Sweden, examined how dendritic cells — a cell in the immune system — work to advance toxoplasmosis, which looks like the flu or may have no symptoms at all. Once dendritic cells become infected, they release GABA, a neurotransmitter that inhibits fear and anxiety.
"This neurotransmitter is essential to move throughout the host," she says. "This allows the parasite to use the cell as what we call the 'Trojan horse.'"
For most individuals, the parasite finds a home in an organ or muscle tissue, where it remains latent as a cyst. The parasite is innocuous in a person with a healthy immune system. Not so for others.
"The problem is when your immune system is compromised," Weidner says. In the early days of the AIDS epidemic, many people died of encephalitis, provoked by the activation of toxoplasma.
Toxoplasmosis can be diagnosed through a simple blood test and treated with anti-parasitic drugs. However, Weidner says it's impossible to locate a cyst in a living person. She says there are several reports of postmortem biopsies on diagnosed schizophrenics, who were found to have several toxoplasma cysts.
Louis Weiss, MD, co-director of the Einstein Global Health Center and professor of medicine and pathology at Albert Einstein College of Medicine, says Weidner's research adds a layer to what scientists have know for decades about the parasite. "The classic experiment has to do with rodents," he explains. "They essentially lose their innate fear of cat urine in a maze."
Weidner says much of the general public is not aware that this parasite is frequently found in raw meat. Around 80 percent of France's population is infected with toxoplasma due to the country's culinary passion for steak tartare and other under-cooked delicacies. In the United States, toxoplasma is the leading cause of food borne illnesses, which is why it's best to take precautions and thoroughly cook your meat, she says.
"I don't think we should be scared of it," says Dr. Weiss. "With an indoor cat that's fed on dry and canned food, the chance that it's going to have toxoplasma is pretty slim. If you're pregnant it's probably not a good idea to do stray cat rescue."
Last Updated: 12/6/2012