Prevalence of active Borrelia burgdorferi infection in small mammals in a southern county of the Twin Cities Minnesota metropolitan area

Lyme disease is the most commonly diagnosed tick-borne illness in Minnesota with 1,050 confirmed cases of Lyme disease and a case rate of 20.1/100,000 people in 2008. The highest prevalence of Lyme disease occurs in the counties north of the Twin Cities metropolitan area. However, in 2008 higher than usual numbers of Ixodese scapularis, the vector of Lyme disease, were reported in some southern metropolitan counties. The goal of this study was to perform a preliminary surveillance of Borrelia burgdorferi infection in small mammals in a previously un-sampled area of a southern metropolitan county. We trapped mammals for 20 consecutive days during September and October of 2009. Skin and joint tissues were collected from white-footed mice (Peromyscus leucopus), southern red-backed voles (Clethrionomys gapperi), and deer mice (Peromyscus maniculatus). DNA was extracted from the tissues and PCR was performed to test for active infection. We found that 13.3% of the animals were positive for B. burgdorferi. Interestingly, while only 18% of the animals trapped were C. gapperi, 62% of these mice were positive for B. burgdorferi. Five percent of P. maniculatus (34% of the mice captured) and 0% of P. leucopus (43% of captured mice) were positive for the bacteria. This preliminary study supports previous observations of increased tick activity in the southern metropolitan counties and is evidence of an active B. burgdorferi infected tick population. In addition, this study suggests that C. gapperi may be an important reservoir in addition to P. leucopus as participating hosts for this infection.