Dangerous Parasite Gains New Attention In Battles Against AIDS, Bioterrorism

Montana State University researchers and their collaborators are gaining widespread attention for discoveries involving a common parasite that can threaten everyone from babies to AIDS patients.

Toxoplasma gondii parasites invade a mouse cell. The parasites are green and the nucleus is blue. (Photo by Jim Ajioka, University of Cambridge)

Their findings about Toxoplasma gondii and toxoplasmosis were published recently in three major scientific journals. Nature published a paper Dec. 20 in its advanced online version. Science published a paper on Dec. 15 and PLoS Pathogens on Oct. 27.

"It's not often you get such a cluster of papers coming out," said Michael White, one of the authors and an MSU professor of veterinary molecular biology. He added that MSU researchers will have another opportunity to explain the studies when they host an international conference on toxoplasmosis from June 29-July 2 at Chico Hot Springs.

Toxoplasmosis is normally associated with medical advice that pregnant women avoid changing cat litter, but it's gaining new attention because of the AIDS epidemic and bioterrorism, the researchers said. Severe toxoplasmosis can cause AIDS patients to go into a deep dementia and become unconscious of their surroundings.

"It's one of the worst syndromes an AIDS patient can die from," said Jay Radke, another of the MSU authors.

Toxoplasmosis is a disease caused by the parasite Toxoplasma gondii. Symptoms usually appear only in people with weakened immune systems, but on rare occasions, healthy people suffer serious eye and central nervous system problems from toxoplasmosis. Their babies can have birth defects. White said toxoplasmosis also may be linked to some cases of schizophrenia and bipolar disease. It can kill livestock and has devastated efforts to restore sea otters near Monterey, Calif. Because it's common, yet complex, toxoplasmosis is a potential weapon for bioterrorists.

People usually acquire toxoplasmosis by eating commercial meat or drinking water that's contaminated with Toxoplasma gondii, White said. They can also pick it up by handling soil or anything that has come in contact with cat feces.

"It's a complex cell just likes ours in terms of metabolism and biochemistry, which makes it a tough nut to crack," White said.

The recently-published studies show that molecular interactions between the parasite and host directly regulate the disease's severity, White said. Genes from the parasite also disrupt signals in the host's immune system and control the establishment of life-long chronic disease.

Genetic crosses produced at MSU were critical in the study that discovered that the parasite dumps a protein into the host to dramatically regulate its immune response, White said. Labs in MSU's Department of Veterinary Molecular Biology and MSU's microarray facility helped establish the role of a second pathogen protein that makes one strain of Toxoplasma especially dangerous.

"Type I strains are extremely important to human medicine as they are disproportionately responsible for inflammation of the brain in AIDS patients and for severe congenital disease that is passed from mother to baby," White said.

MSU led the study that was published in PloS, White said. MSU made major contributions to the Nature and Science papers which were collaborations with Stanford University and Washington University in St. Louis.

The studies give other scientists a model for studying toxoplasmosis or related diseases like malaria and Eimeria, which causes coccidiosis, White added. Eimeria parasites kill chickens and other commercially-raised animals like cattle.

A press release from Washington University said researchers in the future will try to develop more effective treatments against toxoplasmosis by blocking ROP18, the gene largely responsible for making toxoplasmosis so dangerous to humans. The Toxoplasma gondii parasite has approximately 6,000 genes in all. Scientists will also look for other genes that work together with ROP18.

Note: This story has been adapted from a news release issued by Montana State University. via ScienceDaily