Dartmouth researchers expose weakness of common parasite.(Brief Article)

2002 APR 17 - (NewsRx.com & NewsRx.net) -- Dartmouth Medical School geneticists in the Department of Microbiology and Immunology have discovered how to weaken a common human parasite to prevent disease in an animal model after infection by the normal parasite.

The work, reported in the journal Nature (Feb. 2002), opens new avenues for the development of vaccines and other treatments for diseases such as toxoplasmosis caused by a diverse, but related group of protozoan parasites.

Barbara A. Fox, a research associate, and David J. Bzik, PhD, associate professor of microbiology and immunology, found that inactivating a single enzyme in a key biochemical pathway prevented Toxoplasma gondii from causing disease.

The T. gondii parasite, most commonly spread through undercooked meat (and occasionally through cats), causes toxoplasmosis, which generally poses no problems in infected people, but can be life threatening in immunocompromised patients and cause severe birth defects in newborns from primary infections during pregnancy. T. gondii belongs to a family of parasites that include the human pathogens Cryptosporidium parvum, also a danger for immunocompromised patients, and Plasmodium falciparum, a cause of virulent malaria that kills more than 2 million children worldwide each year.

Fox and Bzik have devised a mutant T. gondii strain that causes no disease and, more importantly, provides protection against the normal parasite. "Because of the extraordinary ability of this mutant parasite to infect the animal host without apparent ill effects, this mutant could be used as a prototype vaccine strain," said Bzik.

"This parasite is amenable to further genetic manipulation; it has an amazing ability to elicit a strong immune response that is likely to be beneficial for certain vaccines targeted against other challenging infectious diseases or cancer," added Fox.

"Parasites have been around a long time and have become very proficient at stealing things from their host, if they can. This parasite seemed to rely on just one pathway for obtaining some of the key components of its genetic material. Most other organisms have retained two functional pathways: they can make components new (de novo), or they can salvage them from their nutrient environment, " Bzik explained.