Prevalence of Leptospira spp. in wild brown rats (Rattus norvegicus) on UK farms.

Wild brown rats (Rattus norvegicus) are frequently implicated in the carriage and spread of Leptospira spp. Wild brown rats (n = 259) were trapped from 11 UK farms and tested for Leptospira spp. using a number of diagnostic tests. The prevalence of leptospiral infection was low, but there was variation in the results obtained with the different diagnostic tests. Estimates of prevalence ranged between 0% by silver-staining of tissues, 1% by the microscopic agglutination test, 4% by the enzyme-linked immunosorbent assay, 4% by culture, and 8% by fluorescent antibody technique. In total, 37 (14%) rats were positive by at least one of the tests, which contrasts with the frequently reported prevalences of 50-70% for wild rats in the UK. Serovar bratislava was a prevalent as icterohaemorrhagiae, although it was present only on farms with larger rat populations.