Experimental Infection of Calves with Transfected Attenuated Babesia bovis Expressing the Rhipicephalus microplus Bm86 Antigen and eGFP Marker: Preliminary Studies towards a Dual Anti-Tick/Babesia Vaccine

Abstract

Bovine babesiosis, caused by Babesia bovis and B. bigemina, is a major tick-borne disease of cattle with global economic impact. The disease can be prevented using integrated control measures including attenuated Babesia vaccines, babesicidal drugs, and tick control approaches. Vaccination of cattle with the Rhipicephalus microplus Bm86-based recombinant vaccine reduces the fitness of R. microplus and R. annulatus, but several booster inoculations are required to maintain protection. Herein, we generated a stable transfected strain of B. bovis expressing an enhanced GFP (eGFP) and a chimeric version of Bm86 (B. bovis/Bm86/eGFP). The eGFP was expressed in the parasite cytoplasm, whereas Bm86 was displayed on the surface of merozoites. Three splenectomized calves experimentally infected with B. bovis/Bm86/eGFP showed mild signs of acute disease and developed long-lasting antibody responses to B. bovis and native Bm86. No evidence of sequestration of parasites in the cerebral capillaries was found upon postmortem analysis, confirming attenuation of the strain. This is the first report of transfected B. bovis expressing the tick antigen Bm86 on the merozoite surface that elicits an antibody response to native Bm86. These results represent a proof of concept for a novel live, attenuated, tagged dual-vaccine approach to attempt simultaneous control of babesiosis and tick infestation.

Evolution of Tick Vaccinology Highlights Changes in Paradigms in This Research Area

“…This short time of tick feeding would be enough for the transmission of pathogens [ 20 ], and therefore, interest in the known candidate antigens may be low for their use regarding hypothetical protection in humans. However, other tick-borne pathogens affecting animal health (e.g., Babesia spp., Theileria spp., or Anaplasma marginale ) have been already targeted for control using a vaccination against their main vector [ 21 , 22 ]. In the case of protozoans, such as Babesia or Theileria , the life cycle of the pathogen in the tick vector is different: the protozoan species must complete its life cycle before successful transmission from the tick to the animal, allowing a longer time for the vaccine to interact with the tick feeding.…”

Advances in Babesia Vaccine Development: An Overview

“…Contemporary methods of fighting cattle babesiosis combine tick management, anti- Babesia drugs and vaccination with Babesia -attenuated strains [ 72 ]. It has been discovered that attenuated vaccines are not only effective but also reduce nervous symptoms, as well as reduce the transmission capacity of ticks [ 71 , 73 , 74 , 75 ].…”

“…It has been discovered that attenuated vaccines are not only effective but also reduce nervous symptoms, as well as reduce the transmission capacity of ticks [ 71 , 73 , 74 , 75 ]. The current strategy is a vaccination of less than one-year-old calves in endemic countries [ 72 ]. Conversely, the adult animals can develop acute babesiosis [ 71 , 76 ].…”

“…Pathogen-free animals are infected with a proper parasitic strain and their blood is collected from the jugular vein during the acute phase of the reaction [ 3 , 71 ]. However, as Mazuz et al pointed out, the currently available live attenuated blood-based vaccines present several drawbacks, such as the risk of the transmission of contaminating blood-borne pathogens and potential risks for reversion of virulence [ 72 ]. Furthermore, it is a challenge for supervisors of the process of vaccine production to keep the donors parasite-free, as the preparations are conducted in endemic regions [ 71 ].…”

“…The current research is mainly focused on creating dual vaccines protecting from the babesiosis as well as limiting the vector transmission. This could be achieved by the integration of tick antigens in the vaccine strains [ 71 , 72 , 92 , 93 , 94 ]. Transfection method of knocking out genes of the parasite genome also poses a great and promising solution in the fight against bovine babesiosis.…”