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Description:
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A Babesia sp . isolated from eastern cottontail rabbits (Sylvilagus floridanus ) is
morphologically similar and genetically identical , based on SSU rRNA gene
comparisons , to two agents responsible for human babesiosis in North America and is
closely related to the European parasite , Babesia divergens . The ribosomal RNA (rRNA )
internal transcribed spacer regions (ITS1 and ITS2 ) and the 5 .8S rRNA genes of Babesia
isolates were sequenced and analyzed . The rRNA ITS region sequences of three isolates ,
one each from Kentucky , Massachusetts and Great Britain , considered Babesia
divergens -like organisms , were compared to two Babesia microti isolates , two Babesia
odocoilei isolates and a well defined Babesia divergens isolate . The two B . divergenslike
isolates from North America shared identical rRNA ITS1 -5 .8S -ITS2 region
sequences , and the clones of these isolates clustered into one clade in three phylogenetic
analyses , suggesting that these isolates are conspecific . In vitro comparison of host
erythrocyte specificity between the rabbit Babesia sp . and B . divergens was employed to
discriminate between the two organisms and to determine the usefulness of in vitro
techniques for Babesia sp . characterization . In vitro growth of the rabbit Babesia sp . was
supported in human and cottontail rabbit erythrocytes , but not in bovine cells . Babesia divergens in vitro growth was supported in human and bovine erythrocytes , but
not in cottontail rabbit cells . Morphological characteristics and size differences also
distinguished the two parasites from one another . The erythrocyte specificity and
parasite size differences reported in this study agree with previous in vivo results and
validate the use of in vitro methods for characterization of Babesia species . |