Parasite invasion theory called into question

Parasite invasion theory called into questionLondon, December 24 : A new study has concluded that the current thinking on how the Toxoplasma gondii parasite invades its host is incorrect.

The findings could have implications for other parasites from the same famil, including malaria, and suggest that drugs that are

currently being developed to block this invasion pathway may be unsuccessful.

Toxoplasma gondii is a parasite that commonly infects cats but is also carried by other warm-blooded animals, including


Up to a third of the UK population are chronically infected with the parasite. In most cases the acute infection causes only

flu-like symptoms. However, women who become infected during pregnancy can pass the parasite to their unborn child, which

can result in serious health problems for the baby such as blindness and brain damage.

People who have compromised immunity, such as individuals infected with HIV, are also at risk of serious complication due to

reactivation of dormant cysts found in the brain.

Researchers at the Wellcome Trust Centre for Molecular Parasitology at the University of Glasgow made the discovery using a

new technique to knock out specific genes in the parasite's genome. They specifically looked at three genes that are

considered to be essential for the parasite to invade cells within its host to establish an infection.

"We found that we can remove each of these genes individually and the parasite can still penetrate the host cell, showing for the

first time that they are not essential for host cell invasion as was previously thought. This means that the parasite must have

other invasion strategies at its disposal that need to be investigated," said Dr Markus Meissner, a Wellcome Trust Senior

Research Fellow who led the study.

The genes the researchers looked at form the core of the parasite's gliding machinery that enable it to move around. In the past,

researchers have only ever been able to reduce the expression level of these genes in the parasite, which did lead to a reduction

in host cell invasion but invasion was never blocked completely.

This was attributed to the low levels of gene expression that persisted. However, with the new technique, the team were able to

completely remove the genes of interest. Unexpectedly they found that the parasites were still able to invade.

"One of the genes we looked at is the equivalent of a malaria gene that is a major candidate for vaccine development. Our

findings would suggest that such a vaccine may not be successful at preventing malaria infection and we need to revisit our

understanding of how this family of parasites invades host cells," added Dr Meissner.

As well as malaria, a number of other parasites that affect livestock also belong to the same family. The findings could also

provide clues to new treatments for these diseases, which cause substantial economic losses worldwide.

The study has been published in Nature Methods. (ANI)