When a dangerous animal-borne disease spills over into the human population, a government may be forced to slaughter large numbers of food animals as a control measure, despite considerable economic costs.

This happened in 1999 when Malaysian health authorities were faced with an outbreak of encephalitis among farm workers that had a nearly 50% mortality rate. The cause of the outbreak turned out to be a previously unknown paramyxovirus called the Nipah virus, which is carried by swine. To control the outbreak, millions of pigs were slaughtered within a few weeks, severely harming the Malaysian meat industry. Two years before, a similar precautionary measure was taken by the government of Hong Kong, which arranged the culling of all 1.6 million chickens on Hong Kong Island and the New Territories to prevent chicken-to-human transmission of a virulent avian form of influenza (Box 5).

The costs of measures to control the outbreak of bovine spongiform encephalopathy (BSE, or “mad cow disease”) in the United Kingdom and continental Europe, and the related outbreak of an invariably fatal human neurodegenerative disease (new variant Creutzfeldt-Jakob disease [nvCJD]) have also been high. Ingestion of beef containing the causative agent of BSE (a prion) can result in the development of nvCJD many years later. The export of live cattle and cattle products (other than milk) from the UK has been temporarily banned by the European Commission, and trade in these products has been affected on a global basis. Government officials have come under fire, and consumers across Europe have changed their eating habits due to concern over the spread of BSE. Control measures, including the slaughter of affected cows, have thus far cost the U.K. government an estimated 3.5 billion pounds (about 5 billion U.S. dollars).

The rapidly spreading outbreak of foot-and-mouth disease in Great Britain and continental Europe in 2001 threatens to dwarf the economic costs of the BSE epidemic and devastate the centuries-old British livestock industry. Foot-and-mouth disease does not infect humans but can be spread by travelers who have contaminated soil on their shoes or clothing or who carry contaminated food products. The St. Patrick’s Day parade in Ireland was cancelled due to concerns about spreading the virus, and the British army has been drafted to help bury the carcasses of animals slaughtered because of potential exposure to the disease. Officials credit high-quality animal health surveillance and importation restrictions for the absence of foot-and-mouth disease in the United States, but remain concerned because similar measures have failed to contain the spread of the disease in continental Europe.

These examples demonstrate the potential impact an infectious disease outbreak can have on commerce as well as on human and animal health. If the United States were forced to destroy a significant number of cattle, sheep, pigs, or chickens to control an epidemic, the costs might easily rise into the billions.