Detection and ecology of leptospirosis in Iowa wildlife

To gain additional information on the extent of leptospirosis in wildlife following a human outbreak in Iowa, wild mammals and lower forms of life were collected. Isolation, darkfield microscopic, serologic and pathologic procedures were used to identify past or present evidence of leptospiral infection. Leptospires were isolated from 7 of 75 (9%) mammals. Serotype grippotyphosa was isolated from three raccoons (procyon lotor) and one Western Harvest Mouse (Reithrodontomys megalotis). Serotype ballum was isolated from three opossums (Didelphis marsupialis). Leptospires, unidentified to date, were isolated from frog (Rana pipiens) kidneys. Other positive serologic and pathologic tests gave evidence of infection or previous infection. Utilization of Darkfield microscopic and silver staining techniques did not detect all cases of leptospiral infection. Macroscopic and microscopic serologic methods failed to identify evidence of leptospirosis in all mammals from which leptospires were isolated. Pathologic lesions could only be considered presumptive evidence for leptospirosis. These findings indicate that detection of leptospirosis in wildlife cannot be limited to a single diagnostic test. A combination of diagnostic procedures and clinical evaluation is necessary. Although serotype pomona was implicated as the predominant infecting leptospire in the human cases and domestic animals and was isolated from water at a swimming site, only serotypes grippotyphosa, ballum and ICF (frog isolate) were isolated from wild mammals and lower forms of life in the same vicinity.