Almost 2000 Australian babies are born each year with CMV – a virus contracted from their mother that can leave them with permanent disabilities such as blindness, developmental delays, epilepsy and cerebral palsy.

It's an infection contracted in the womb. Working with scientists from Canada and Europe, Monash University structural immunologist Richard Berry has established how the virus avoids detection – raising the prospect of new drugs to help the body fight the enemy within.

A member of the herpes family, CMV can lie dormant and undetected for years – living in the body without coming under attack from the immune system. Why this is so had remained a mystery.

But now the international team has answered the 40-year-old question as to why cytomegalovirus, or CMV, is so sneaky and successful.

Researchers found the virus, which infects more than 50 per cent of adults, is a master at flying under the radar of the body's immune system because it tricks it into thinking infected cells are healthy cells.

Using the Australian Synchrotron in Clayton to image the virus at an atomic level in never-before-seen detail, the researchers were able to witness for the first time how the virus did this.

In the body, cells have markers on the surface that act like signposts telling the immune system it is a healthy cell. If infected, however, the markers go missing – alerting the immune system to an infected cell.

"But this virus has screwed up this process because it has a protein which pretends to be the cell's marker, so the immune system thinks it is a healthy cell," Dr Berry, from the ARC Centre for Advanced Molecular Imaging, said.

 CMV had a large genome which included genes that were constantly evolving to change their disguise and stay ahead of the body's immune system, he said.

But the body's defensive immune receptors were also evolving repeatedly. 

"It's like an evolutionary arms race," Dr Berry said. "But at the moment it looks like the virus is winning."

CMV lies dormant until the body is weakened. When the body is vulnerable, it strikes. In healthy people, CMV causes a mild flu-like illness that lasts a few days or weeks. In susceptible people, such as those with suppressed immunity or unborn babies, CMV can be a dangerous infection.

A mother can pass on the virus only if she contracts CMV during pregnancy. There is then a one-in-three chance of CMV being contracted by the fetus.

Of the 1800 babies born in Australia with CMV each year, about 380 will have a permanent disability, making it the leading cause of birth defects in the Western world. In rare cases the infection can be fatal.

"It can be quite a serious issue and the symptoms for congenital CMV quite nasty," Dr Berry said.

"This work has given us an understanding of how the virus invades the immune system, and understanding that process will help design therapeutics to help the body to combat that."

The findings are published in the journal Cell.