Incidence of leptospirosis in the detroit rat population.

The rat population (Rattus norvegicus) in the city of Detroit was surveyed to determine the incidence of leptospirosis. Four methods of survey were used--serological, direct examination of urine, culture of urine, kidney and brain, and histopathological examination. Of 358 sera tested by the microscopic-agglutination test, 277 (77.4%) had significant agglutinins for serotype icterohaemorrhagiae. Significant differences were found between adult and young animals in both incidence and antibody titers, titers of 1:50 or higher being present in 90.3% and 38.8%, respectively, of adult and young rats. Examination of freshly drawn urine by dark field microscopy revealed that 59.6% of the animals were shedding leptospirae. When stained with Steiner's silver stain, 91.9% of the kidney sections were positive for leptospirae, showing this to be the most sensitive test of those used. Leptospirae were isolated from one or more cultures of kidney, urine, or brain from 221 (59.2%) of the 358 rats examined.