Just a few cans of poison could trigger nightmare

Since a cult released Sarin gas on the Tokyo subway in 1995, governments have woken up to the dangers of biological attack

The greatest fear of the medical authorities is that an outbreak of disease caused by a terrorist attack would overwhelm the health services.

The greatest fear of the medical authorities is that an outbreak of disease caused by a terrorist attack would overwhelm the health services.

Two years ago, the US Secretary of State for Defence, William Cohen, raised a 5lb bag of sugar on television to demonstrate the amount of anthrax spores that could kill 50 per cent of Washington's 600,000 population.

Anthrax has attracted the most attention as a biological agent because, in its spore form, it would be easy to carry and distribute by aerosol. But in its early stages the effects would be difficult to distinguish from other naturally occurring illnesses.

Anthrax attacks the respiratory tract and, over a period of a week following a release, increasing numbers of patients would report to their GPs and Accident and Emergency Departments complaining of fever, aches and pains, symptoms similar to the flu.

Increasing numbers of patients would then develop septicaemia (blood poisoning) and deaths would start to occur. By the time the diagnosis of anthrax was made, the initial exposure of perhaps several hundred individuals would have spread to tens of thousands through contact with family members, work colleagues and medical staff.

The only treatment is high doses of antibiotics. There is a vaccine but it is kept in very limited quantities. In the nightmare scenario, the population would be gripped by panic and hospitals would be besieged by mobs demanding drugs and vaccination.

One of the main areas of concern is being able to distinguish quickly between a natural outbreak of a contagious disease and an epidemic generated by a biological weapon. In 1998, an outbreak of the Hanta virus in the US, which is spread by rats and is lethal in humans, was initially thought to be triggered by terrorists. It took scientists nearly a week to establish that it was a natural emergence of the disease.

In September last year, a killer virus spread by mosquitoes caused alarm in New York. It turned out to be a strain of West Nile virus, never seen before in the city, and there was speculation that it was the work of Iraqi agents. Six months earlier an Iraqi dissident had claimed that Saddam Hussein had threatened to release a modified strain of West Nile virus against his enemies.

However, experts pointed out that the virus had been spreading steadily into new regions for several years and it was an odd choice for terrorists since most victims recovered in a few days.

The attack using Sarin gas by the Japanese religious cult Aum Shinrikyo in 1995 served as a wake up call to the world of the threat from biological weapons, especially in cities with an underground system. The terrorists released the gas on Tokyo's subway where it would disperse more slowly and have the maximum lethal effect. Twelve people died in the attack and over 5,000 were affected.

Among the possible agents that could be used, concern has been expressed that clandestine stocks of smallpox virus may exist outside the two approved storage locations in the US and Russia where samples have been kept since the disease was eradicated in 1980. They are needed to produce vaccine should the disease ever recur.

The existing supply of smallpox vaccine is estimated at 50 to 100 million doses worldwide, of which six to seven million are in the US, enough to protect only a tiny proportion of those potentially at risk. In the event of an outbreak it would take two to three years to set up manufacturing facilities to produce a sufficient supply.

Fear of biological terrorism in the US has become as unnerving as the threat itself. President Clinton's public declaration that he expected a terrorist attack using biological or chemical weapons within the next five years has fuelled alarm and provided fertile ground for hoaxers.

On Christmas Eve 1998, police in protective clothing and masks surrounded a department store in Palm desert, California, and herded 200 people doing their last minute shopping into the car park where they were ordered to strip before being hosed down with a bleach solution. An anonymous caller had claimed that anthrax spores had been released into the air-conditioning, but tests found nothing. Similar hoaxes have been reported across the country in their scores.