TM

It doesn't take an exotic virus like Ebola to transform the U.S. into a hot zone. A single case of smallpox could put the entire nation at risk. The smallpox virus is highly contagious and would spread quickly because Americans are not vaccinated. Routine inoculations were halted in 1972. People vaccinated before 1972 lost most of their immunity within 10 years.

A terrorist who wanted to launch a smallpox attack, however, would probably have a very hard time getting hold of the virus. Smallpox was eradicated in 1980. Officially, only two stores of the virus exist, for research purposes, in secure locations in the U.S. and Russia. There may be covert stashes in Iraq, North Korea and Russia, but these countries would be reluctant to release them, fearing a smallpox epidemic among their own unvaccinated people. Even if a terrorist were successful in obtaining the virus, his plans could backfire: smallpox is so contagious that the first victims are likely to be the members of his own terrorist cell.

Many bacterial agents can be used as bioweapons, including Clostridium botulinum (botulism) and Yersinia pestis (plague). But anthrax stands out because its spores are particularly hardy; they are resistant to sunlight, heat and disinfectant, and can remain active in soil and water for years. Anthrax occurs naturally in both wild and domestic animals including cattle, sheep and camels. Infection from direct contact with affected animals is fatal in 20% of cases. If inhaled, however, anthrax spores cause death in almost 90% of the time.

Yet manufacturing sufficient quantities of any bacteria in a stable form is a technical and scientific challenge; plague bugs, for example, degrade within hours when exposed to the sun, and anthrax spores tend to clump together in humid conditions. The Japanese cult Aum Shinrikyo sprayed anthrax and botulism eight times over parts of Tokyo without effect.

Despite all the attention being given crop dusters, using one to spread germs is not as easy as it sounds. The planes are designed to spray pesticides in heavy, concentrated streams, whereas bioweapons are ideally scattered in a fine mist over as large an area as possible. The nozzles in crop dusters are best suited to discharging relatively large particles 100 microns in diameter not tiny one-micron specks of bacteria.

Unlike biological agents, which are living organisms that require proper conditions to survive, chemical weapons such as the nerve gases sarin and VX are relatively easy to acquire and stockpile. Chemicals are difficult to manufacture in sufficient quantities for a large-scale attack, however; more likely are isolated assaults such as the 1995 sarin attack on a Tokyo subway that injured thousands and killed 12.

As Oregon's Rajneeshee Cult demonstrated in 1984, it is not difficult to set off a wave of food poisonings. Indeed, gastroenteritis caused by natural contamination and careless food handling afflicts millions and results in 5,000 deaths each year. The Rajneeshees considered a number of different viruses and bacteria, including those that cause hepatitis and typhus, but decided for their purposes (disrupting the outcome of a local election) on a strain of salmonella that would be debilitating but not fatal. Salmonella poisonings tend to be localized. With proper hygiene, the bacterium is not particularly contagious.

An even easier bug to obtain is the familiar intestinal parasite E. coli. Naturally occurring outbreaks of E. coli, typically the result of fecal contamination in everything from hamburgers to swimming pools, sicken hundreds of thousands of Americans each year. In New York City this spring, a man was arrested after he was spotted spraying what turned out to be feces-laden water over the contents of a midtown salad bar (fortunately, no one got sick). A far more virulent strain of the bacterium called O157:H7 is sometimes fatal, but identifying and isolating the right strain is beyond the technical capabilities of most terrorists.

A terrorist attack aimed at crops and livestock would be less dramatic but might cause more disruption in the long run. Such attempts are not unheard of. In World War II, Britain accused Germany of dropping small, cardboard bombs filled with beetle pests on English potato fields, and in the 1980s Tamil militants threatened to target Sri Lankan tea and rubber plantations with plant pathogens. Perhaps the most worrisome threat to U.S. agriculture is foot-and-mouth disease, which can spread with astonishing speed in sheep, cattle and swine. Not seen in this country since 1929, the disease is harmless to humans but renders farm animals economically worthless. The U.S. could be forced to destroy much of its own livestock, as Great Britain had to do earlier this year.