Residual effect of antibabesial drugs on the live redwater blood vaccines

Erythrocyte invasion by Babesia parasites: Current advances in the elucidation of the molecular interactions between the protozoan ligands and host receptors in the invasion stage

During an asexual growth cycle of Babesia parasites in a natural host, the extracellular merozoites invade (i.e., attach to, penetrate, and internalize) the host erythrocytes (RBC) via multiple adhesive interactions of several protozoan ligands with the target receptors on the host cell surface. After internalizing the host RBC, they asexually multiply, egress from the RBC by rupturing the host cells, and then invade the new RBC again. In the invasion stage, several surface-coating molecules of merozoites might be involved in the initial attachment to the RBC, while proteins secreted from apical organelles (rhoptry, microneme, and spherical body) are proposed to play roles mainly in erythrocyte penetration or internalization. On the other hand, several components located on the surface of the RBC, such as sialic acid residues, protease-sensitive proteins, or sulphated glycosaminoglycans, are identified or suspected as the host receptors of erythrocyte invasion by Babesia parasites. The detailed molecular interactions between Babesia merozoites and the host RBC are incompletely understood. In this review, these identified or suspected molecules (protozoan ligands/erythrocyte receptors) are described by especially focusing on Babesia bovis.

Live vaccines against bovine babesiosis

Bovine babesiosis is an important tick-borne disease caused by Babesia bovis, B. bigemina and B. divergens. The first steps taken in the development of an effective vaccination strategy against bovine babesiosis followed the observations that animals, recovered from natural infection with Babesia were strongly protected against subsequent challenge. Further investigation indicated that the use of donor blood from recovered animals to infect recipient animals did not produce the severe form of the disease. The past century has seen a refinement of this original carrier-donor system to one using attenuated less virulent strains with standardized doses of known parasite concentration to ensure reliability. With the implementation of good manufacturing practices further changes were necessary in the production of these vaccines, such as freezing for long-term storage to allow sufficient time for pre-release safety and effectivity testing. Regardless of these improvements the vaccines are not without problems and breakdowns and breakthroughs occur from time to time. Despite considerable research efforts into the development of alternative more consumer friendly vaccines, none is immediately forthcoming and the live attenuated babesiosis vaccines are still used in many countries.