Genetic engineering without unwanted side effects helps fight parasites

Modified CRISPR-Cas9 gene editing scissors are enabling researchers at the University of Zurich to make alterations to the genetic material of single-cell organisms that are indistinguishable from natural mutations.

This method makes it possible to develop a harmless experimental live vaccine for the widespread parasite Toxoplasma gondii.

Around a third of the world's population carries Toxoplasma gondii, a parasite that puts people with a weakened immune system at risk and can trigger malformations in the womb. The single-celled pathogen also leads to economic losses in agriculture, with toxoplasmosis increasing the risk of abortion among sheep, for example.

The parasite has a complex life cycle and infects virtually all warm-blooded creatures, including wild rodents and birds. It is introduced into livestock, and thus into humans, exclusively via cats. In cats, infectious stages form that are shed in feces into the environment as encapsulated oocysts, and from there, enter the food chain.

"If we succeed in preventing the production of these oocysts, we can reduce the occurrence of toxoplasmosis among humans and animals," says Adrian Hehl, professor of parasitology and Vice Dean of Research and Academic Career Development at the University of Zurich's Vetsuisse Faculty.