title: Tick passage results in enhanced attenuation of Babesia bovis.
abstract: Serial blood passage of virulent Babesia bovis in splenectomized cattle results in attenuated derivatives that do not cause neurologic disease. Tick transmissibility can be lost with attenuation, but when retained, attenuated B. bovis can revert to virulence following tick passage. This study provides data showing that tick passage of the partially attenuated B. bovis T2Bo derivative strain further decreased virulence compared with intravenous inoculation of the same strain in infected animals. Ticks that acquired virulent or attenuated parasites by feeding on infected cattle were transmission fed on naive, splenectomized animals. While there was no significant difference between groups in the number of parasites in the midgut, hemolymph, or eggs of replete female ticks after acquisition feeding, animals infected with the attenuated parasites after tick transmission showed no clinical signs of babesiosis, unlike those receiving intravenous challenge with the same attenuated strain prior to tick passage. Additionally, there were significantly fewer parasites in blood and tissues of animals infected with tick-passaged attenuated parasites. Sequencing analysis of select B. bovis genes before and after tick passage showed significant differences in parasite genotypes in both peripheral blood and cerebral samples. These results provide evidence that not only is tick transmissibility retained by the attenuated T2Bo strain, but also it results in enhanced attenuation and is accompanied by expansion of parasite subpopulations during tick passage that may be associated with the change in disease phenotype.
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA kss@vetmed.wsu.edu.
authors.forename: Kerry S
authors.initials: KS
authors.lastname: Sondgeroth
authors.affiliation: Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA.
authors.forename: Terry F
authors.initials: TF
authors.lastname: McElwain
authors.affiliation: Animal Disease Research Unit, USDA Agricultural Research Service, Pullman, Washington, USA.
authors.forename: Massaro W
authors.initials: MW
authors.lastname: Ueti
authors.affiliation: Animal Disease Research Unit, USDA Agricultural Research Service, Pullman, Washington, USA.
authors.forename: Glen A
authors.initials: GA
authors.lastname: Scoles
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Reif
authors.affiliation: Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA Paul G. Allen School for Global Animal Health, College of Veterinary Medicine, Washington State University, Pullman, Washington, USA.
authors.forename: Audrey O T
authors.initials: AO
authors.lastname: Lau
mesh_terms: D000818:Animals; D016793:Babesia bovis / Q000472:pathogenicity*; D001404:Babesiosis / Q000469:parasitology / Q000473:pathology / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology* / Q000473:pathology; D004252:DNA Mutational Analysis; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D005260:Female; D008297:Male; D009154:Mutation; D017422:Sequence Analysis, DNA; D013987:Ticks / Q000469:parasitology*; D014774:Virulence
chemical_list: D016054:DNA, Protozoan
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