The fear of biological weapons such as anthrax may be more likely to create illness than the weapons themselves, say experts.

Long-term social or psychological damage could be the result of panic caused by the news of anthrax attacks.

A letter to the British Medical Journal from researchers in the UK, US and Australia predicted that while bioweapons themselves might not kill many people, for many more, their prospect is having a devastating effect.

Already, there are reports of mass "sociogenic" illness - on 29 September, paint fumes set off a bioterrorism scare at a school in Washington State, sending 16 students and a teacher to the hospital.

The general level of malaise, fear and anxiety may remain high for years

BMJ research

Just after the beginning of the current anthrax scare a liquid, which turned out to be window cleaning fluid, was sprayed at a Maryland subway station.

As many as 35 people reported nausea, headache and sore throat.

The experts, including Professor Simon Wessely, from Guy's, King's and St Thomas' Hospital in London, conclude that a series of hoaxes and actual attacks could have a significant effect.

They write: "It is customary to expect large scale panic if such weapons are every effectively deployed or thought to be deployed.

Distrust of health officials

"The general level of malaise, fear and anxiety may remain high for years, exacerbating pre-existing psychiatric disorders and further heightening the risk of mass sociogenic illness.

"The current uncertainty over the chronic health effects of low level exposure to toxic agents will further increase anxiety in the affected communities."

They add that because health officials will not be able to provide "blanket" assurances about long-term safety, the public may lose trust in experts.

"Unconfirmed or controversial hypotheses about the health effects of exposure to chemical and biological weapons will probably become contentious scientific and media issues."