Toxoplasma‘s reach extends far beyond the world of cat and mouse. It may have a special relationship with rodent and feline hosts, but this parasite also infects the brains of billions of animals on land, at sea and in the air. Humans are no exception. Worldwide, scientists estimate that as many as three billion people may be carrying Toxoplasma. In the U.S., there is a one-in-five chance that Toxoplasma parasites are lodged in your neural circuits, and infection rates are as high as 95 percent in other countries.
For most people, this infection appears asymptomatic, but recent evidence shows that Toxoplasma actively remodels the molecular landscape of mammalian brain cells. Now some researchers have begun to speculate that this tiny single-celled organism may be tweaking human health and personalities in stealthy, subtle ways.
What the cat dragged in
Researchers first discovered T. gondii in 1908, and by the end of the 20th century they had a good grasp on how people could pick up this parasite. The story starts with cats: for reasons that scientists have yet to unravel, Toxoplasma can sexually reproduce only in the feline gut. The parasite breeds within its feline host and is released from the feline’s tail end. Cats are such obsessive groomers that it is rarely found in their fur. Instead people can become infected from kitty litter or by ingesting it in contaminated water or food.
Within a new host the parasite begins
dividing asexually and spreading throughout the host’s body. During this initial stage of the infection, Toxoplasma can cause the disease toxoplasmosis in immunocompromised or otherwise susceptible hosts, leading to extensive tissue damage. Pregnant women are …