Epidemiology and Infection

Original Papers

Animal and human health

High prevalence of Leptospira spp. in sewer rats (Rattus norvegicus)

L. H. KRØJGAARDa1a2a4 c1, S. VILLUMSENa2, M. D. K. MARKUSSENa4, J. S. JENSENa2, H. LEIRSa4a3 and A.-C. HEIBERGa4

a1 Department of Biology, University of Copenhagen, Denmark

a2 Statens Serum Institut, Department of Bacteriology, Mycology and Parasitology, Copenhagen, Denmark

a3 Danish Pest Infestation Laboratory, Department of Integrated Pest Management, University of Aarhus, Denmark

a4 Department of Biology, University of Antwerp, Belgium


Earlier studies on the ecology of leptospirosis in temperate regions focused mainly on free-ranging rats in rural areas. Here we report on the occurrence of Leptospira spp. in Rattus norvegicus living in sewers in a suburban area in Copenhagen, Denmark. In 2006–2007, about 30 rats were captured in sewers at each of six different locations. Rat kidneys were screened by PCR for pathogenic Leptospira spp. In one location no infected rats were found, whereas the prevalence in the remaining five locations ranged between 48% and 89%. Micro-agglutination tests showed that serogroup Pomona, Sejroe, and Icterohaemorrhagiae were the most common. Infection was related to age with the highest prevalence observed for adult rats but there was no difference in infection rate between sexes, suggesting primarily environmental transmission. Since most reported rat problems in urban areas are related to sewer rats, the surprisingly high level of infection calls for an increased public health concern.

(Accepted March 24 2009)

(Online publication April 27 2009)


c1 Author for correspondence: L. H. Krøjgaard, Statens Serum Institut, Department of Bacteriology, Mycology and Parasitiology, building 43, room 317, Artillerivej 5, 2300 Copenhagen S, Denmark. (Email: lkd@ssi.dk)