The strain was isolated in 1948 from a pig in rasil by Guida (1948), who also did some serological typing (Guida, 1952). However, Wolff and Bohlander (1960) described the strain as a new 'subserovar' of L. tarassovi, named guidae, ref. strin RP 29. The strain is first mentioned in the list of 1965 (WHO, 1965) as a separate serovar.