A swine disease of unknown etiology was described in 1987 by veterinarians and researchers in the United States. Since no known pathogens could be implicated, it was believed to be unique. This decision was based on the disease's severity and duration as well as a combination of reproductive and respiratory signs. Within three years of its discovery, clinical signs of the "mystery swine disease" were reported in all principal areas of swine production in the United States. Months later, a syndrome similar to the U.S. "mysterious disease" was reported from across the Atlantic Ocean - Germany.