Peromyscus leucopus and Microtus pennsylvanicus simultaneously infected with Borrelia burgdorferi and Babesia microti.

Borrelia burgdorferi, the etiologic agent of Lyme disease, and Babesia microti, the causative agent of human babesiosis, were isolated from 71 and 57%, respectively, of 14 specimens of Peromyscus leucopus and Microtus pennsylvanicus collected from Prudence and Patience Islands, R.I. Both pathogens were isolated from five individual rodents. The presence of these two infectious organisms in the same mammal suggests that individual larval Ixodes dammini may ingest both pathogens and subsequently transmit them in the nymphal stage.