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.

Universiẗat, Diss., 2004--München.

Growing incidence of infections caused by the tick-transmitted protozoan parasite Babesia spp. defines babesiosis as an emerging disease from the aspect of human and veterinary medicine. The thesis provides an insight to biology of two main agents of human babesiosis, Babesia microti and Babesia divergens. We introduce here the fully optimized quantification model of Babesia parasite enabling the detailed investigation of the parasite developmental cycle and identification of molecules playing a role in its acquisition and transmission by the vector Ixodes ricinus. Novel and detailed information about Babesia dissemination within the tick tissues are given by newly implemented visualization and quantification techniques. Special emphasis is paid to parasite development in the tick salivary glands, the primary site responsible for parasite transmission from the vector into the host. Using gene-specific silencing we screene the tick immune pathways including effector molecules and evaluate their role in Babesia acquisition. We also provide a detailed view to Babesia parasite sexual commitment by monitoring its kinetics upon various stimuli. Moreover, a new direction of anti-babesial therapy is proposed by validation of the Babesia proteasome as a drug target. Overall, the research presented in the thesis extends the current knowledge of the Babesia parasite biology including molecular interactions at the tick-Babesia interface and thereby could significantly contribute to a potential control of babesiosis.