Germ warfare

LONDON — "Poisons and pathogenic microorganisms are among the natural health hazards with which human beings are obliged to co-exist; difficult to perceive and therefore to avoid, they present a threat that is insidious as well as damaging or deadly." This statement, at the beginning of a recent draft report by the World Health Organisation on the threat of biological warfare, sums up the fear and defencelessness many people feel about potential weapons of terrorism that cannot be seen or heard, yet have the capacity to wreak widespread destruction.The report, released in the wake of the attack on the World Trade Centre in New York on September 11, was accompanied by a dire warning from the WHO that governments needed to prepare responses to biological or chemical attacks by terrorist extremists. That warning has already prompted the UK Health Secretary Alan Milburn to order National Health Service chiefs to update contingency plans for dealing with an attack.But many questions remain unanswered about the feasibility of chemical or biological attacks on large populations and which, if any, are the most likely weapons of choice. The WHO report makes it clear that, in terms of scale, attacks could fall anywhere between "relative insignificance" at one end to "mass destruction of life" at the other. Yet it also stresses that the greater the mass-destructive power of the weapon, the greater the practical difficulties of achieving it. "While thousands of toxic chemicals and pathogenic microorganisms have been investigated for their potential utility as weapons, few have been judged as satisfactory candidates and even fewer have found their way into weapons and actually been used," the WHO report states.In order to be effective as a weapon, it adds, it's not enough for terrorists simply to produce a harmful agent. They must also ensure it is stable enough to resist degradation during handling and storage and the energy-transfer processes most likely needed to disseminate the organism.Other constraints include the need to deliver the weapon to its target population, ensuring it loses none of its toxicity, infectivity and virulence in the process and controlling its movement and dilution in the atmosphere.Exposure to the agents would most likely be by inhalation or contact with the skin. In order to be inhaled, a chemical or biological weapon must comprise a vapour made up of particles in a diameter range of 0.6 to 5μm — small enough to be respirable and penetrate to the alveoli deep in the lungs but not so small that they fail to be deposited and are instead simply exhaled.For a contaminated vapour or aerosol to reach its target group depends largely on how atmospheric turbulence affects its distribution. If the atmosphere is stable, states the WHO report, dosages may reach hazardous levels, even several kilometres downwind of the source. On the other hand, air currents could divert dangerous particles vertically and away from those on the ground.Inhalation is recognised as the most likely transmission route for both biological and chemical weapons, the report adds. "The body is most vulnerable to this route of exposure because of the large surface area and gas-exchange function of the lungs, the susceptibility of mucous membranes to infection and also the presence of phagocytic cells that, if unsuccessful in destroying a pathogenic microorganism, may instead carry it to the lymph system where it can proliferate and cause systemic infection."Much of the recent media speculation has focused on the potential for attacks involving dangerous bacteria, toxins and viral agents such as anthrax, smallpox, plague and botulinum toxin.For some — like smallpox — an attack would rely on the transmission of the disease from one infected person to another. Others, like the poison botulinum toxin, would probably be transmitted through contaminated foodstuffs.The Public Health Laboratory Service — the UK government body that monitors communicable diseases — has been updating its briefing documents on several organisms thought to be potential germ warfare candidates.Anthrax, a bacterial infection caused by the Bacillus anthracis, is rarely transmitted from person-to-person. Instead, it is either caught through cutaneous exposure — often through direct contact with the skin or tissues of infected animals — or inhalation of anthrax spores. The respiratory form is often fatal but can be treated effectively with antibiotics if caught early and an effective vaccine already exists to protect those most at risk.Smallpox, a disease eradicated in 1973 through global vaccination programmes, is caused by the variola virus. Transmission is through inhalation of virus particles during close contact with an infected person and in the first two weeks of illness — when lesions in the mouth ulcerate and produce lots of airborne virus — the potential for it to spread is significant. Once infection has occurred, there are no drugs to treat the virus — instead doctors can only treat the symptoms.Botulism, is caused by a poison produced by the bacterium Clostridium botulinum, and is fatal in up to 10% of cases. The organism itself causes no harm; instead, it's the toxin it releases which causes symptoms such as blurred vision, difficulty swallowing and speaking, diarrhoea, vomiting and — eventually — paralysis. C. botulinum is an anaerobic bacterium, and is often caught when the spores have got into an airtight environment such as a tin or jar, and is particularly common in home-prepared foods preserved in oil. An antidote can be administered that can block the effects of the toxin but artificial ventilation of the patient is often required because of respiratory failure.Although a vaccine exists against botulism, the PHLS says it is not widely used because there are concerns about its effectiveness and it also has significant side effects.According to Simon Whitby, research fellow at the Department of Peace Studies, University of Bradford, the obstacles facing a terrorist launch of a biological weapon are considerable but not entirely insurmountable. "There are some fairly formidable hurdles to overcome. First you've got to get a virulent strain of a pathogen; then you've got to produce it in sufficient quantities, which has biological safety hazards involved for those producing it. "Also, you've got to somehow develop a method of disseminating it and this has some quite exacting technological characteristics. With anthrax, for example, you've got to produce an aerosol cloud of the right size particles for effective inhalation. And a lot of pathogens are highly sensitive to ultraviolet light and radiation, as well as the effects of wind and rain."Whitby believes anthrax or botulinum toxin would be the favoured agents for terrorist exploitation. There is also the possibility that they could be genetically modified to improve their stability and, in the case of anthrax, enhance their resistance to antibiotics. "But terrorists would need to be extremely well resourced to do that," he said. "I would guess they would be more inclined to use conventional explosives rather than a biological weapon."

Germ warfare

The attack on the World Trade Center has increased speculation that populations could be at risk from terrorist attacks with biological and chemical weapons.

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