Dissertation
The Evaluation of Cerebral Sequestration and Tick Transmissibility in Virulent and Attenuated Strains of Babesia bovis.
Doctor of Philosophy (PhD), Washington State University
01/2013
Handle:
https://hdl.handle.net/2376/117966
Abstract
Neurological signs develop during acute infection by virulent strains of Babesia bovis in cattle. Serial passage of virulent strains in cattle results in attenuated derivatives that do not cause neurologic disease. We evaluated in vivo whether an attenuated strain loses its ability to sequester in cerebral capillaries by examining brain biopsies during acute infection. Next we tested whether tick passage would result in reversion to neurovirulence with an associated change in sequestration phenotype.
Cerebral biopsies of spleen intact animals inoculated intravenously with a parental virulent or derived attenuated strain of B. bovis were evaluated for capillary sequestration: (1) at the onset of clinical babesiosis; and (2) during severe clinical disease. In animals infected with the virulent strain, there was a significant increase in sequestration between the first and second biopsy. The attenuated strain, while still capable of sequestration at a significantly reduced level, did not change between the first and second sampling. Necropsy examination confirmed the second biopsy findings and demonstrated that sequestration identified at necropsy reflects pathologic changes occurring in live animals.
Tick passage of virulent B. bovis did not alter the clinical or pathologic phenotype, resulting in acute, severe babesiosis with cerebral sequestration in splenectomized calves exposed to infected larvae. In contrast, tick passage of the attenuated strain resulted in loss of sequestration in cerebral capillaries, and qPCR analysis detected a significant difference in parasite level detected between animals infected with the virulent or attenuated derivative. However, the only tick tissue in which the virulent strain was significantly increased compared to the attenuated strain was the ovary. Thus differences in clinical phenotype and parasitemia are likely not due to higher numbers of parasites in the tick tissues of the virulent strain. Sequencing analyses of three biomarker genes indicate that diverse genotypes of the attenuated strain are selected within the tick vector.
In conclusion, not only does the derived attenuated strain maintain tick transmissibility, it does not revert to virulence following tick passage. The lack of clinical signs and sequestration after passage within the tick, suggests that there may be other factors that mediate cerebral sequestration leading to neurovirulence.
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Details
- Title
- The Evaluation of Cerebral Sequestration and Tick Transmissibility in Virulent and Attenuated Strains of Babesia bovis.
- Creators
- Kerry S. Sondgeroth
- Contributors
- Audrey O.T. Lau (Advisor)Terry F. McElwain (Committee Member)Guy H. Palmer (Committee Member)Kelly Brayton (Committee Member)Carlos Suarez (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Veterinary Medicine, College of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 59
- Identifiers
- 99900581740001842
- Language
- English
- Resource Type
- Dissertation