Björn Sigurdsson (1913-1959) was director of the Keldur Institute for Experimental Pathology in Iceland from 1948 until his untimely death at the age of 46 in 1959. He and his co-workers isolated and characterized virus from sheep with maedi (an Icelandic word for dyspnea) and visna (meaning wasting). Transmission experiments indicated that visna and maedi were different organ manifestations of infection with the same virus, thus giving rise to the present name, maedi-visna virus. On the basis of these diseases, Sigurdsson formulated the concept of slow infections as different from acute and chronic infections. The lentiviruses derive their name from Sigurdsson´s concept of slow infections.