The strain was isolated from a rat (Rattus norvegicus) in Manila sometime during the years 1957-1959 and described as a new serovar name manile, ref. strain LT 398 (Galton et al., 1963). The new serovar first appears in the list of 1965 (WHO, 1965) with the footnote "Provisional clasisification pending further work". In the list of 1967 (WHO, 1967) it is included as a recognized serovar.