The Parasite that Gave Cats a Bad Name

Author: John Monczunski

Nested somewhere deep in your body may be a tiny, strange parasite called Toxoplasma gondii. Anywhere from one-third to one-half of all U.S. adults are believed to be infected with the parasite, popularly identified with cats. Most people never know it, though, because “toxo” doesn’t do anything bad unless your immune system isn’t working properly. The parasite encysts itself and lies dormant, periodically emerging only to be suppressed by the body’s immune system.

Among AIDS patients and others with compromised immune systems, however, the parasite infection can be lethal. Pregnant women are especially at risk because they can pass the parasite to their unborn infants, with devastating consequences. Toxoplasmosis is the major cause of neurological defects in newborns, causing blindness, learning disabilities, impairment of fine motor skills and, in some cases, encephalitis.

There is no vaccine for the disease among humans, and drugs used to treat it can in some cases have severe digestive side effects. “A lot of ‘shake and bake’ quick fixes haven’t worked so we’re going back to first principles, trying to understand how the organism works at a very basic level, and from that develop a strategy to defeat it,” says Kristin Hager, Notre Dame assistant professor of biological sciences.

Specifically Hager hopes to learn exactly how Toxoplasma secretes certain proteins that help it invade host cells. The instant the parasite contacts a host cell, a variety of proteins are secreted which push into the cell, hijack nutrients, and set up a space where they can divide, she explains.

“When I entered the field everyone was interested in the proteins. The problem is we found out very little that was directly useful. I’ve gone back a step to thinking about how these proteins are made.” Precisely, she is interested in how the proteins are “packaged” and moved to specific places in the cell. Hager has found that certain molecules surrounding the proteins act as a “train ticket,” telling them where to go in the cell.

“If you can block production of these [invasion] proteins, you can stop the infection. This is the Achilles’ heel. That’s the best-case scenario we’re working toward, but it’s a long way down the road.”

John Monczunski is an associate editor of this magazine.