About a third of these women will pass the virus on to their babies.

ECONOMIST: A global disaster

There are currently 33, 200 people in the UK infected with HIV - a third of whom are unaware they have the virus.

BBC: World Aids Day

The third point that you made had to do with the H1N1 virus.

WHITEHOUSE: "White House to Main Street" Town Hall: Elyria, OH

This third way is to insert their genes into another, more conventional virus instead of a traditional animal host.

ECONOMIST: Foulpox

Meanwhile, the chief veterinary officer for Northern Ireland has said there was concern that a third flock of sheep may be infected by the foot-and-mouth virus.

BBC: Foot-and-mouth hits Irish Republic

The death toll from US cases of West Nile virus, which has killed scores of people, has risen by nearly a third in a week, according to health officials.

BBC: West Nile virus death toll in US jumps by a third

Up to a third of cases are fatal and those who survive may face memory loss, impaired cognition and motor difficulties (the virus affects the nervous system).

CNN: ON DEADLY GROUND