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About a third of the world’s population carries Toxoplasma gondii, a parasite that endangers people with weakened immune systems and can trigger birth defects in the uterus. The single-celled pathogen also causes economic losses in agriculture, with toxoplasmosis increasing the risk of abortion in sheep, for example.
The parasite has a complex life cycle and infests virtually all warm-blooded creatures, including wild rodents and birds. It is introduced into cattle, and therefore into humans, exclusively via cats. It is only in this main host that infectious stages are formed which are released with the faeces into the environment in the form of encapsulated oocysts and from there enter the food chain.
“If we are successful in preventing the production of these oocysts, we can reduce the occurrence of toxoplasmosis in humans and animals,” says Adrian Hehl, professor of parasitology and associate dean of research and academic career development at the Vetsuisse faculty of the University of Zurich. He and his research group have developed methods for such an intervention.
Live vaccine protects cats from natural infections
In previous research, the team had already identified various genes responsible for the formation of oocysts. This allowed them to develop a live vaccine against toxoplasmosis: researchers can use the CRISPR-Cas9 gene-editing scissors to turn off these essential genes and infect or inoculate cats with the modified parasites. These pathogens do not produce infectious oocysts, but still protect cats from natural infection by Toxoplasm in nature.
Handling without side effects
To make the sterile parasites, the researchers used the CRISPR-Cas9 gene editing scissors. While this allows precise modifications to the genetic material, depending on the protocol, the method typically used can also have drawbacks. Unintentional genetic mistakes and alterations can creep in. The research group around Hehl reports that in Toxoplasm, these unwanted side effects can be avoided by using a modified technique.
For editing the CRISPR-Cas9 gene, scientists usually insert a ring-shaped piece of DNA, a so-called plasmid, into the cell. This contains all the information needed to create the gene scissors and the elements that recognize the desired place in the genetic material. The cell thus produces all the components of the gene scissors itself. Subsequently, however, the plasmid remains in the cell and can trigger additional unplanned genetic changes.
Gene scissors disappear without a trace
The method used by the Zurich team works differently. Researchers assemble the pre-programmed gene scissors outside the cell and then implant them directly into the parasites. Once the genetic material has been manipulated, the components are very quickly broken down completely, only the desired modification remains.
“Our approach is not only faster, cheaper and more efficient than conventional methods. It also makes it possible to modify the genomic sequence without leaving traces in the cell, ”explains Hehl. “This means that we can now make experimental live vaccines without plasmids or incorporating resistance genes.”
Legislation on genetic engineering is lagging behind
Faced with these results, Hehl questions the federal government’s plans to subject the editing of the CRISPR-Cas9 genome to the existing law on genetic engineering (and to the moratorium, which has been extended until 2025): “Our method is a good example of the difference between this new technology and conventional approaches to genetic engineering. “He says it is now possible to inactivate a gene without leaving unwanted traces in the genetic material, in a way that is indistinguishable from natural mutations. Unlike many other controversial applications of genetic engineering, this procedure nor does it affect food production and therefore does not constitute a direct intervention in the food chain.
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Material provided by University of Zurich. Note: Content can be changed for style and length.
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