Löff·ler \ˈlœf-lər\ , Friedrich August Johannes (1852–1915), German bacteriologist. Löffler contributed greatly to the advancement of bacteriology. In 1882 he discovered the bacterium of the genus Pseudomonas (P. mallei) that causes glanders. He discovered the cause of swine erysipelas and swine plague in 1885. With Paul Frosch (1860–1928) he determined in 1897 that foot-and-mouth disease is caused by a virus. This marked the first time that the cause of an animal disease was attributed to a virus. They developed a serum against the disease in 1899. The diphtheria bacillus discovered by Klebs in 1883 was isolated in the following year by Löffler, who also published the first full description of the microorganism which is now known as the Klebs-Löffler bacillus.