Identification of novel immune correlates of protection against acute bovine babesiosis by superinfecting cattle with in vitro culture attenuated and virulent Babesia bovis strains

Abstract

The apicomplexan tickborne parasites Babesia bovis and B. bigemina are the major causative agents of bovine babesiosis, a disease that negatively affects the cattle industry and food safety around the world. The absence of correlates of protection represents one major impediment for the development of effective and sustainable vaccines against bovine babesiosis. Herein we superinfected cattle with attenuated and virulent strains of B. bovis to investigate immune correlates of protection against acute bovine babesiosis. Three 6-month-old Holstein calves were infected intravenously (IV) with the in vitro culture attenuated Att-S74-T3Bo B. bovis strain (106 infected bovine red blood cells (iRBC)/calf) while three age-matched Holstein calves were inoculated IV with normal RBC as controls (106 RBC/calf). All Att-S74-T3Bo-infected calves showed a significant increase in temperature early after inoculation but recovered without treatment. Att-S74-T3Bo-infected calves also developed: (a) monocytosis, neutropenia, and CD4+ lymphopenia in peripheral blood on days 3 to 7 post-inoculation; (b) significant levels of TNFα, CXCL10, IFNγ, IL-4, and IL-10 in sera at day 6 after infection; and (c) IgM and IgG against B. bovis antigens, starting at days 10 and 30 post-inoculation, respectively. At 46 days post-Att-S74-T3Bo inoculation, all experimental calves were infected IV with the homologous virulent B. bovis strain Vir-S74-T3Bo (107 iRBC/calf). All Att-S74-T3Bo-infected calves survived superinfection with Vir-S74-T3Bo without displaying signs of acute babesiosis. In contrast, control animals showed signs of acute disease, starting at day 10 post-Vir-S74-T3Bo infection, and two of them were humanely euthanized at days 13 and 14 after inoculation due to the severity of their symptoms. Also, control calves showed higher (P<0.05) parasite load in peripheral blood compared to animals previously exposed to Att-S74-T3Bo. No significant alterations in the profile of leukocytes and cytokines were observed in Att-S74-T3Bo-inoculated after Vir-S74-T3Bo infection. In conclusion, data demonstrate novel changes in the profile of blood immune cells and cytokine expression in peripheral blood that are associated with protection against acute bovine babesiosis. These identified immune correlates of protection may be useful for designing effective and sustainable vaccines against babesiosis in cattle.

Vaccination with an in vitro culture attenuated Babesia bovis strain safely protects highly susceptible adult cattle against acute bovine babesiosis

“…highly susceptible adult cattle. In this study we started addressing these two concerns by using Att-S74-T3Bo, a previously defined in vitro culture attenuated strain of B. bovis (24)(25)(26). Despite of the reduced number of animals used in the present study, the data support the hypotheses that vaccination with Att-S74-T3Bo is safe for highly susceptible adult cattle and that it induces protection against challenge with a virulent homologous B. bovis strain.…”

“…By using a sensitive method for cytokine detection and a systemic approach to investigate alterations of leukocytes in peripheral blood after vaccination and challenge, we identified markers for protection and disease progression in highly susceptible adult cattle. Considering this and previous studies, we are building a solid body of information on the Att-S74-T3Bo strain (24)(25)(26)50). It is now known that this attenuated long-term cultured B. bovis strain presents a low population complexity compared to its parental strain (24), it is not tick-transmissible (25), and it protects calves against challenge with homologous virulent strain (26).…”

“…Considering this and previous studies, we are building a solid body of information on the Att-S74-T3Bo strain (24)(25)(26)50). It is now known that this attenuated long-term cultured B. bovis strain presents a low population complexity compared to its parental strain (24), it is not tick-transmissible (25), and it protects calves against challenge with homologous virulent strain (26). Results from this study increment previous knowledge and provide additional evidence on the safety and efficacy of Att-S74-T3Bo in protecting adult cattle against acute bovine babesiosis.…”

Retrospective study of the epidemiological risk and serological diagnosis of human babesiosis in Asturias, Northwestern Spain

“…As for infections caused by other Babesia species [34,35], additional studies are needed to evaluate the humoral immune response during mono-and double infections with B. divergens and B. burgdorferi s.l. and to identify antigens that elicit the production of protective antibodies or determine whether a patient, even an externally healthy blood donor, has an acute, chronic or past B.divergens infection.…”

A conserved motif in the immune-subdominant RAP-1 related antigen of Babesia bovis contains a B-cell epitope recognized by antibodies from protected cattle

“…Pre-immune and immune sera from the B. bovis experimentally infected cattle used in the ELISA analysis were generated in a previous study ( 30 , 31 ).…”