A mother's fear of disease during pregnancy could strengthen a baby boy's immune system, according to new research.

They do not have to be exposed to the infection themselves, but only perceive the threat of illness from being close to those suffering from it for resistance to be passed on to their offspring, researchers found.

Scientists have long known a mother's experiences before and during pregnancy can have profound effects on her children's development. However, a new study provides the first evidence that fears about disease in the mother's environment has a dramatic influence on the next generation's health and behaviour.

Pregnant mice housed near males that were infected with a parasite produced sons with better natural resistance to the disease, as well as lower aggression and social dominance in adult life.

The mothers were not infected and it is not known how the pregnant mice detected the presence of disease in their neighbours. Researchers say the effect is likely to be repeated in other animals and possibly humans.

Dr Olivia Curno of Nottingham University, who led the research, said: "It seems the mothers are priming their offspring for the environment they will live in. When the risk of disease is high, improved immunity may outweigh any costs associated with reduced social dominance."

The study is published today in the journal Proceedings of the Royal Society.