London: Scientists in Britain are trying to investigate the reason why the common parasite Toxoplasma, does not cause harm to most people, but could make many others seriously ill.

Toxoplasma is a genus of parasitic protozoa which is carried by cats, but can also be passed on by many other warm-blooded animals, even humans. Toxoplasma causes the disease called toxoplasmosis, which in normal circumstances is not harmful, but can spark off life-threatening effects on an unborn human fetus, and can be the cause of many side effects.

The study published in Nature indicates that Toxoplasma is very dangerous for those who suffer weakened immune systems, for example those with HIV. In such cases, Toxoplasma can cause brain damage or even death.

The recent study demonstrates how the parasite actually injects a single protein into a cell that it intends to attack, and how this protein heads for the nucleus of the cell and hampers the ability of the cell to elicit an immune defense.

According to Susan Coller, one of the researchers leading the project, "The nucleus is the heart of the cell, the ultimate prize. If you want to affect the cell in a dramatic way, go straight there."

Additionally, the scientists also discovered that there were subtle discrepancies in this crucial protein between different types of Toxoplasma. It is thought that each diverse strain could contaminate different types of host cell with the least damage.

According to Professor John Barrett, a senior lecturer in parasitology at the University of Aberystwyth, "The effect on the fetus can be very serious and there is a reliable test for Toxoplasma, so in these higher risk groups, it may be worthwhile."