Leptospirosis in man and animals has been studied in Denmark since 1934. Strains of the following ten serotypes have been isolated: icteroluienwrrhagiae, poi, canicola, bellum, bratislava, pomono, grippotyphosa, sejroe, saxkoebing, and bataviae. Twenty-eight of the 44 species of wild land mammals living in Denmark have been examined culturally. Leptospires of eight serotypes were isolated from 14 species. Leptospires were demonstrated microscopically in the urine and/or kidneys of 31 bats belonging to four species. These leptospires could not be cultured in vitro or transmitted to animals other than bats. Serological evidence of present or past leptospirosis was found in four species of Lagomorpha, Carnivora and Ungulata not examined culturally.

Our findings indicate that the following species are maintaining hosts for leptospires of identified serotypes in Denmark: Sorex araneus (poi), Erinaceus europaeus (bratislava), Microtus arvalis (grippotyphosa), Rattus norvegicus (icterohaemorrhagiae), Mus musculus (sejroe), Apodemus agrarius (pomona), and Apodemus flavicollis (saxkoebing). Mus musculus is probably also a maintenance host for leptospires of the ballum serotype. Three bat species, Myotis daubentonii, Pipistrellus pipistrellus, and Nyctalus noctula, with a high carrier rate (15–20%), may be maintenance hosts for unknown serotypes of a unique group of leptospires. Bataviae and canicola leptospires have not yet been isolated from wild animals in Denmark.

The significance of leptospirosis in wild mammals for the epidemiology of leptospirosis in man and domestic animals is discussed.