Is there an antidote?

Anthrax is caused by the bacterium Bacillus anthacis

An antitoxin is available, but it is only effective if administered early in the course of the disease. There is also a vaccine, but concerns about its effectiveness and possible side-effects mean it is not widely used.

Availability
The bacterium from which botulism is derived occurs naturally in the ground, so many samples are likely to be held around the world. The Japanese cult Aum Shikrikyo dispersed it in aerosols on at least three occasions in the early 1990s. According to John Eldridge, the editor of Jane's Nuclear, Biological and Chemical Defence, Iraq, Russia and Iran are likely to have large quantities at their disposal.

Overall risk
One problem for health experts would be distinguishing a terrorist attack from a natural outbreak of food poisoning.

John Eldridge said: "Botulism toxin was considered by coalition forces to be a viable threat during the Gulf War. Some 10,335 kg was destroyed under UNSCOM [United Nations Special Commission] supervision."

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Smallpox

What is it?
Smallpox is a viral infection caused by the variola virus. One of the biggest killers in history, the disease was effectively wiped out in the 1970s by a worldwide vaccination plan.

Symptoms
The incubation period is about 12 days. First symptoms include fever, tiredness and an aching head and back. Over the next few days, a distinctive rash develops, usually on the face, legs and arms.

Lesions then appear, which form crusts and fall away within a few weeks. Death occurs in up to 30% of cases.

How is it spread?
Smallpox can be caught by inhaling the virus from an infected person. Sufferers are most infectious during the first week of illness.

In the event of a purposeful attack, the virus could be released in an aerosol, or suicide attackers could deliberately infect themselves. Its stability in air and high infection rate make the smallpox virus potentially very dangerous.

Is there an antidote?
There is a vaccine against smallpox but routine public inoculation ended in the 1970s as incidence of the disease declined. Everyone born before 1972 was vaccinated, but immunity has probably worn off by now.

In people exposed to smallpox, the vaccine can lessen the severity of, or even prevent, illness if given within four days of exposure. The US currently has an emergency supply of the vaccine.

There is no proven treatment for smallpox victims - except supportive therapy to combat the symptoms.

Availability
There are two World Health Organisation-approved repositories of variola virus - one at the US Center for Disease Control and the other in Novosibirsk, Russia.

The extent of secret stockpiles in other parts of the world remains unknown, but according to Jane's Defence, Iraq and Russia are likely to have the virus.

Overall risk
Smallpox is often cited as the most feared biological weapon. There is no proven treatment, and the virus could race through a population before anyone realises it has been released.

According to John Eldridge: "It is possible that cultures have found their way out of Russia and could be in the hands of terrorists."

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Plague

What is it?
Plague is an acute bacterial infection caused by Yersinia pestis. There are two main strains - bubonic and pneumonic.

Symptoms

India had an outbreak of pneumonic plague in 1994

In bubonic plague, the bacteria invade the body causing swollen lymph nodes and fever. The less frequent pneumonic plague causes severe respiratory problems, including coughing and breathing difficulties. The incubation period is usually between one and seven days.

How is it spread?
Bubonic plague is generally not spread from person to person, except through direct contact with fluids from the swellings. The disease is mainly transmitted from the bite of infected fleas carried by rodents.

But pneumonic plague can be passed on by face-to-face contact, through the inhalation of bacteria from a sneeze or cough of an infected person.

Terrorists would most likely attack by spraying an aerosol containing plague bacteria, causing the pneumonic variety.

Is there an antidote?
Plague can be effectively treated with antibiotics such as streptomycin and tetracycline. In treated cases, death occurs in fewer than 5% of victims, but if left untreated mortality rates can be higher than 90%. There is no vaccine.

Availability
Natural outbreaks of plague still occur - most notably in Africa, Asia and western USA. The bacterium responsible is also widely available in microbe banks around the world.

According to Jane's Defence, America, Iraq, Russia, Iran and possibly North Korea have supplies of the bacterium.

Overall risk
Pneumonic plague is less virulent than smallpox but more so than anthrax. John Eldridge said: "Plague is a possible low-tech choice as successful vectors include insects and rodents."

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Tularaemia

What is it?
Francisella tularensis, the organism that causes tularaemia, is one of the most infectious bacteria known.

Symptoms
Symptoms vary according to the method of infection. If the bacteria are inhaled, symptoms can be similar to pneumonia.

Victims who ingest the bacteria may get a sore throat, abdominal pain, diarrhoea and vomiting. Untreated, the disease could progress to respiratory failure, shock and eventually death. The overall mortality rate is about 5%.

How is it spread?
Tularaemia is not spread though human-to-human transmission. Many small mammals harbour the disease, and naturally-acquired human infection occurs through animal bites, ingestion of contaminated food or water and inhalation of infective aerosols.

Aerosol dispersal would be the most likely method of terrorist attack.

Is there an antidote?
There is an effective vaccine, and the disease is treatable with antibiotics.

Availability

Quarantine is used to prevent the spread of Ebola in Africa

During World War II, the potential of F. tularensis as a biological weapon was studied by both sides.

Tularaemia was one of the biological weapons stockpiled by the US military in the late 1960s, but the supply was subsequently destroyed.

The Soviet Union continued production into the early 1990s. Jane's Defence believe that Iraq and Russia are likely to have stockpiles of this bacterium.

Overall risk
Tularaemia is considered to be dangerous because of its extreme infectivity and because it is easily spread. But it would not kill the vast majority of those infected.

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Haemorrhagic fever

What is it?
The most well-known haemorrhagic fever is Ebola, caused by a virus of the same name. A similar disease, also found in the tropics, is caused by the Marburg virus. Both are lethal and relatively easily transmitted.

Symptoms
Within a few weeks of exposure, ebola victims suffer from headaches and muscle aches. They may also experience nausea, chest pain and profuse bleeding. More than half of all Ebola sufferers die from the disease.

How is it spread?
The virus can spread from person to person, through direct contact with blood or other secretions.

Is there an antidote?
For both Ebola and Marburg, there is no cure, no vaccine and no treatment.

Availability
Like cholera and typhoid, these diseases are endemic in many poor countries. There is also speculation that the Soviets experimented with the Marburg virus for its use as a biological weapon.

Overall risk
Haemorrhagic fevers are unlikely to be an obvious choice as they are so hazardous to work with. But, said John Eldridge, perpetrators could quickly acquire the capability to use these germs as weapons.

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Crop diseases

Many countries have investigated the effects of purposefully inflicting crop diseases on an enemy. Japan, Germany, France, Britain, the former Soviet Union and the US have all - at various stages - invested in anti-crop warfare of various kinds.

Potato blight, soybean rot and diseases that can affect staple crops like wheat and rye are all capable of decimating huge swathes of agricultural land. So too are infestations by insects such as the Colorado and rapeseed beetle.

The potato blight of 19th Century Ireland and the brown spot disease responsible for the Bengal famine in 1942 show just how devastating these crop diseases can be.

Many developing countries are largely reliant on rice

Dr Simon Whitby, from the Department of Peace Studies at Bradford University, said that while attacking a crop is unlikely to cause widespread starvation in anywhere but the very poorest countries - those largely reliant on one staple crop - the method could still be effective as an "economic weapon" elsewhere.

This is especially true when the agriculture is concentrated on intensive farming of genetically similar crops.

"There would be social disruption at one end of the scale, and starvation at the other," he said.

Two of the main crop diseases identified as potential bio-weapons are wheat stem rust and rice blast.

Rice blast

What is it?

This is one of the most important rice diseases and is caused by the fungus Pyricularia oryzae. There are 219 types, so breeding a resistant crop is complex.

Characteristics

Grey-white lesions appear on the leaves, which eventually produce a brown margin when the lesion stops growing. The fungus may also attack the stem of the plant. Yield losses may be large as few seeds are likely to develop.

Availability

The US chose blast disease as its main anti-rice agent. The US anti-crop programme, an intensive operation throughout the 1950s and 60s, had a cache of nearly a tonne of rice blast at the time it was disbanded. The stockpile would have been intended for a potential attack on Asia, said Dr Simon Whitby.

Other countries apart from the US are also likely to have investigated this disease as a biological weapon, but information is limited.

Overall risk

Rice blast is a fungal disease, in which thousands of spores form on the infected plant. These spores multiply rapidly and float through the air infecting other plants. This easy dispersal, coupled with the complexity of breeding resistant plants, make rice blast a potentially dangerous biological weapon.

Wheat stem rust

What is it?

Stem rust is caused by the fungus Puccinia graminis tritici.

Characteristics

Dark red postules appear on both sides of the leaves and stems of the infected plant. As well as attacking wheat, the fungus can also affect barley, rye and other grasses.

Availability

Between 1951 and 1969, the US stockpiled more than 30,000 kg of wheat stem rust spores, which Dr Simon Whitby estimated is probably enough, in theory at least, to infect every wheat plant on the planet.

The US used to have a stockpile of over 30,000 kg of anti-wheat spores

The US also developed means of disseminating the spores. An early design, according to Dr Whitby, was a 500-lb bomb originally designed to release propaganda leaflets. Instead it was packed with bird feathers which carried the fungal spores.

Other countries have also investigated the use of wheat diseases in biological warfare. Dr Simon Whitby said: "Iraq has looked into its military capability and has carried out limited testing. The potential target was probably Iran."

And the USSR's huge programme in the 1970s, mostly concentrated on wheat diseases, is believed to have employed 10,000 personnel working solely on agricultural biowarfare, said Dr Whitby.

Overall risk

As stem rust is a fungal disease, the spores are easily dispersed in air. The use of resistant wheat strains limits its effectiveness as a biological weapon, but it still has the potential to be dangerous.

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Animal diseases

The warfaring potential of diseases that affect animals is often overlooked. "This is a new type of hazard," said John Eldridge, from Jane's Defence. "In the UK we are already experiencing the effects of one of the most virulent animal pathogens, from a natural outbreak of foot-and-mouth disease."

According to Piers Millett, a specialist in anti-animal biowarfare from the Department of Peace Studies at Bradford University, the main targets for terrorists are likely to be rinderpest, anthrax, foot and mouth, swine fever and Newcastle disease, which affects poultry.

Could foot-and-mouth disease be used as a biological weapon?

During the two world wars, both sides investigated the capability of anti-animal weapons. In World War I, Germany conducted a sabotage programme infecting animals destined for use on the battlefield.

In World War II, the British trials of anthrax infection on Gruinard Island off the coast of Scotland rendered the island uninhabitable for almost 50 years.

The Americans also experimented with rinderpest and swine fever, but according to Piers Millett, this was abandoned through fear of spreading the disease to America's own cattle. "The last thing you want to do is end up infecting your own country," he said.

Other countries such as Russia, Iraq and Japan have also investigated biowarfare of this kind, and Piers Millett said that anti-animal weapons were technologically easier to develop than anti-crop weapons.

While unlikely to kill humans, a biological attack on livestock can have severe results.

According to Piers Millett, "The recent foot and mouth disease in the UK is a good simulation of what a biological attack of this nature would look like."

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