Many food security experts say the biological weapon they fear most is foot-and-mouth disease (FMD), a virus that doesn't threaten people but devastates cloven-hoofed animals such as cattle and swine. The disease causes fever and large blisters in the mouth, on the teats and between the hooves, making it difficult for the animal to eat, drink and walk. Though most animals recover, their milk and meat productivity is generally lost. FMD is a major threat because infecting just one steer with the contagious virus could, within days, lead to the infection of hundreds of thousands of cattle. FMD is not found in North or Central America, Australia, New Zealand, Russia and the European Union, but it is found in much of the rest of the world and could be brought into the United States by a terrorist or by accident, says Roger Breeze, CEO of the Centaur Science Group, in a recent paper on agroterrorism. The last U.S. outbreak was in California in 1929. There are at least seven types of FMD virus and many subtypes. Vaccination against one type does not protect against others. U.S. cattle are not vaccinated for FMD. The disease can be spread in any number of ways, including by the introduction of an infected animal into a herd, a person with contaminated manure on his shoe, and contaminated water or feed. "You don't need to be a scientist or have access to some secret lab; you don't have to buy technology or expertise to make it an effective weapon. And it's widely available," says Jerry Jaax, a former Army biodefense and biological arms control specialist and now associate vice provost for research compliance and university veterinarian at Kansas State University.Once an infection takes place, it can spread with frightening ease; virus-laced aerosol droplets can even spread for miles through the air. The traditional response by authorities to such an outbreak is to kill, burn and bury the affected herds. The potential economic impact of an FMD outbreak in the United States could be $40 billion to $60 billion, according to USDA estimates.The following is a sketch of how an FMD outbreak could play out, how it could be introduced into livestock and what the consequences of an attack might be.A terrorist smuggles the FMD virus into the U.S.The terrorist spends a few weeks or months surveilling a ranch in the Midwest. Under the cloak of night, he introduces the virus into the herd.The disease spreads undetected. Thousands of infected cattle are sent from the ranch to a feedlot, which can hold 30,000 to 50,000 animals. Every day thousands of animals are sent to a local slaughter facility, where they're handled by hundreds of workers. Hundreds or thousands more infected cattle from the herd are also transported to other slaughtering facilities, where they infect additional cattle. Others move on to auction barns, where they come into contact with even more cattle. The highly concentrated nature of cattle production (huge feedlots, rapid transportation, large processing facilities) eases the speedy spread of the disease throughout the country.Up to 14 days after INFECTION, symptoms begin to appear. When a rancher notices a sick cow, she calls the local veterinarian, who contacts a federal foreign disease official. That official sends virus samples to the USDA's Plum Island Animal Disease Center in Orient Point, N.Y., or to the National Veterinary Services Laboratories in Ames, Iowa. It can take up to four days to diagnose the virus. In the meantime, the infected herd and, possibly, neighboring herds are under strict quarantine.Once FMD is identified, the infected herd and all susceptible animals within a two-mile radius of the affected farm must be killed, burned and buried, according to Roger Breeze, CEO of the Centaur Science Group.Infected herds are similarly killed and buried in other affected counties and states. Halts on transporting cattle and quarantines go into effect in those areas. Nevil Speer, an associate professor of animal science at Western Kentucky University's agriculture department who has studied the economic effects of an FMD attack, says he projects that halts on shipments and quarantines in the Kansas-Texas region, in which 40 percent of the nation's slaughtering capability is located, would result in lost cattle sales of $207 million a day. U.S. export of meat is banned by other countries until the government is sure that FMD is stamped out.Consumer fears about beef lead to a drop in domestic consumption.The slaughter of hundreds of thousands of animals occurs, with millions of Americans viewing video of the results. Many are repulsed at the killings and wonder why they are necessary. Some blame the government for failing to prevent the FMD attack. Even though the virus doesn't threaten people, fears of another attack arise.Economic losses reach the billions. The loss of livestock is multiplied by upstream and downstream costs (such as cleaning and disinfecting costs, inability to restock herds until safe, rebuilding costs to producers, government compensation costs, loss of business in meat processing and related animal-products industries, losses in tourism and hunting industries in affected areas, law enforcement costs).