Seroprevalence of Leptospira in rattus norvegicus in Grenada, West Indies.

OBJECTIVE To determine the seroprevalence of Leptospira and the serovars responsible for Leptospira exposure in rats in Grenada in order to assess rats as a reservoir host for human infection. DESIGN AND METHODS Rattus norvegicus rodents were collected from each of the six parishes on the island of Grenada. Serum from 237 rats was tested by the microscopic agglutination test (MAT) and an Immunoglobulin G (IgG) Enzyme-Linked Immunosorbent Assay (ELISA). Seroprevalence rates among parishes were compared using a chi-squared test of homogeneity. RESULTS Of the 237 serum samples tested, 64 were positive by either MAT or ELISA for an overall seroprevalence of 27%. The ELISA identified 24.5% (57/233) of the rats positive at a titer of > or = 1:160. The MAT identified 7.1% (13/183) of the rats positive at a titer of > or = 1:100. Six of the 13 MAT positive samples had antibodies to multiple serovars. The serovars identified by the MAT with the greatest frequency were from the Icterohaemorrhagiae serogroup. Two rats had antibodies for serogroup Cynopteri, the first time this serogroup has been identified in Grenada. CONCLUSIONS Our results for Leptospira exposure in rats in Grenada support R norvegicus as an important reservoir host for Leptospira, particularly those from the Icterohaemorrhagiae serogroup. Because this serogroup is the primary serogroup responsible for documented human exposure in Grenada, exposed rats represent a public health threat.