The sequence of Giardia small subunit rRNA shows that voles and muskrats are parasitized by a unique species Giardia microti

The small subunit ribosomal RNA (eukaryotic 165 rRNA) gene from Giardia trophozoites, isolated from 8 different prairie voles and 8 different muskrats, was amplified by the polymerase chain reaction. The 165 rDNA was sequenced in its entirety for 2 prairie volt and 2 muskrat Giardia. In addition, the 5' 500 nucleotides of the 165 rDNA from Giardia isolates from each of 6 voles and 6 muskrats were amplified and sequenced. The results show that Giardia from voles and muskrats are very similar to each other but differ substantially from Giardia isolated from humans. We believe that the Giardia isolate from voles and muskrats constitutes a distinct species, which will be referred to as Giardia microti. These results suggest that both volts and muskrats are parasitized by the same species of Giardia, that this species is different from the Giardia that parasitizes humans, and that voles and muskrats do nor contribute to the zoonotic character of human giardiasis.