countries to be in one of three disease states with regard to FMD: FMD present with or without vaccination, FMD-free with vaccination, and FMD-free without vaccination. Countries designated FMD-free without vaccination have the greatest access to export markets, so many developed nations, including Canada, the United States, and the UK, work hard to maintain their current status. Some countries such as Brazil and Argentina, which have large beef-exporting industries, practise vaccination in some areas, but have other vaccination-free zones. Reasons cited for restricting export from countries using FMD vaccines include, probably most importantly, routine blood tests relying on antibodies cannot distinguish between an infected and a vaccinated animal, which severely hampers screening of animals used in export products, risking a spread of FMD to importing countries. A widespread preventive vaccination would also conceal the existence of the virus in a country. From there, it could potentially spread to countries without vaccine programs. Lastly, an animal infected shortly after being vaccinated can harbor and spread FMD without showing symptoms itself, hindering containment and culling of sick animals as a remedy. Many early vaccines used dead samples of the FMD virus to inoculate animals, but those early vaccines sometimes caused real outbreaks. In the 1970s, scientists discovered that a vaccine could be made using only a single key protein from the virus. The task was to produce enough quantities of the protein to be used in the vaccination. On June 18, 1981, the US government announced the creation of a vaccine targeted against FMD, the world's first genetically engineered vaccine. The North American FMD Vaccine Bank is housed at the United States Department of Agriculture's Foreign Animal Disease Diagnostic Laboratory at Plum Island Animal Disease Center. The center, located off the coast of Long Island, New York, is the only place in the United States where scientists can conduct research and diagnostic work on highly contagious animal diseases such as FMD. Because of this limitation, US companies working on FMD usually use facilities in other countries where such diseases are endemic. Epidemiology United States (1870–1929) The US has had nine FMD outbreaks since it was first recognized on the northeastern coast in 1870; the most devastating happened in 1914. It originated from Michigan, but its entry into the stockyards in Chicago turned it into an epizootic. About 3,500 livestock herds were infected across the US, totaling over 170,000 cattle, sheep, and swine.