Transmissibility of Babesia bigemina and Babesia bovis attenuated strains by Rhipicephalus (Boophilus) microplus ticks.

摘要

To assess transmissibility of attenuated Babesia bigemina (BIS) and Babesia bovis (BOR) strains by Rhipicephalus microplus (R. microplus), 12 steers from a tick-free area were divided in four groups and infested at different intervals with R. microplus larvae. One animal from each group was inoculated with 1x108 infected erythrocytes (IE) of attenuated BIS, BOR, virulent B. bigemina, or B. bovis field strains. Two additional serial passages were performed (syringe passages), and engorged female ticks were collected coincident with presence of IE in blood of infected steers. The offspring larvae were utilized to feed upon an additional group of recipient steers (tick passages). All needle passages were successful for inducing infection in steers that received both, the attenuated and field strains. Kinetes were detected in hemolymph of engorged female ticks fed on steers infected with virulent B. bigemina and B. bovis field strains. However, kinetes were not detected in hemolymph samples from ticks collected from the steers inoculated with the attenuated strains. All recipient steers infested with larvae from ticks that fed on steers infected with virulent strains became Babesia positive. By contrast, steers infested with larvae from ticks that fed on animals inoculated with attenuated strains were negative, except for the recipient steer receiving larvae from the third syringe passage of BIS and BOR. These strains could be safer to use as live immunogens in animals, as their virulence and ability to be transmitted by the tick is impaired at least after two blood passages in cattle.