The findings may offer a new approach for vaccination against infections caused by parasites

Dr David Bzik

A team from the Dartmouth Medical School in New Hampshire, US, were able to disarm the parasite Toxoplasma gondii, which is related to the malaria parasite and is found in undercooked meat.

When the researches injected the mutant form of the parasite into laboratory mice they found it was harmless.

Immune response

Better still, the mutant parasites stimulated a potent immune response that protected the mice from later infection with the wild-type parasite.

Researcher Dr David Bzik said: "The findings have important implications for developing chemotherapy against parasitic infections and they may offer a new approach for vaccination against infections caused by parasites."

The researchers rendered the parasite harmless by knocking out a single enzyme.

This destroyed the parasite's ability to reproduce itself and survive in its host.

One dose of the normal parasite is enough to kill a mouse with a suppressed immune system.

But when the scientists injected millions of the altered parasites into weakened mice it did not harm the animals.

They believe the same technique might work against other parasitic diseases.

Dr Bzik said: "We were expecting to observe a modest difference between the virulence of the mutant compared to its highly virulent parent.

"Instead, the mutant did not cause any disease in a mouse model."

Serious disease

In most humans Toxoplasma gondii infection causes no symptoms.

However, under some conditions, toxoplasmosis can cause hepatitis, pneumonia, blindness, and severe neurological disorders.

People whose immune system is weakened, for instance Aids patients, are particularly at risk.

The disease can also be transmitted from a mother to her unborn baby, resulting in miscarriage or disability.

The research is published in the journal Nature.