THE SEQUENCE OF GIARDIA SMALL-SUBUNIT RIBOSOMAL-RNA SHOWS THAT VOLES AND MUSKRATS ARE PARASITIZED BY A UNIQUE SPECIES GIARDIA-MICROTI

The small subunit ribosomal RNA (eukaryotic 165 rRNA) gene from Giardi a trophozoites, isolated from 8 different prairie voles and 8 differen t muskrats, was amplified by the polymerase chain reaction. The 165 rD NA was sequenced in its entirety for 2 prairie volt and 2 muskrat Giar dia. In addition, the 5' 500 nucleotides of the 165 rDNA from Giardia isolates from each of 6 voles and 6 muskrats were amplified and sequen ced. The results show that Giardia from voles and muskrats are very si milar to each other but differ substantially from Giardia isolated fro m humans. We believe that the Giardia isolate from voles and muskrats constitutes a distinct species, which will be referred to as Giardia m icroti. These results suggest that both volts and muskrats are parasit ized by the same species of Giardia, that this species is different fr om the Giardia that parasitizes humans, and that voles and muskrats do nor contribute to the zoonotic character of human giardiasis.