Invasion, and short- and long-term survival of Babesia divergens (Phylum Apicomplexa) cultures in non-bovine sera and erythrocytes.

The research team investigated whether Babesia divergens, a parasite that typically infects bovine, can survive and thrive in human, sheep, and horse erythrocytes (red blood cells). It was found that the parasite was able to invade all tested erythrocyte types and long-term survival was particularly successful in human erythrocytes. The goal of this was to explore the possibility of creating a live vaccine free of bovine material contaminants.

The need for the study

• The study aims to produce a Babesia divergens vaccine that is free from bovine material contaminants.
• This parasite primarily infects cattle, causing babesiosis, a tick-borne malaria-like illness. It has also been shown to cross-infect humans, causing severe symptoms, particularly in individuals who have had their spleen removed.
• The researchers investigated whether this parasite could be maintained in different types of erythrocytes from humans, sheep, and horses. This is to potentially leverage the parasite’s adaptability for the production of more acceptable vaccines.

Research Method and Findings

• The study demonstrated that B. divergens can successfully grow in human, sheep, and horse red blood cells, and serum-free medium.
• B. divergens was even successfully maintained in bovine erythrocytes overlaid with serum-free HL-1 medium, setting the foundation for a bovine-material-free cultivation method.
• Parasite growth was improved with bovine and sheep serum supplements, while horse and human serums hampered growth. This was monitored via measuring parasitaemia (the presence of parasites in the blood) and the uptake of tritiated hypoxanthine (a marker for DNA replication and thus cellular proliferation).
• The parasite was able to invade all types of erythrocytes, but polyparasitism (the occurrence of more than one parasite in a single host cell) was less commonplace in sheep and horse erythrocytes than in bovine and human ones.
• Unfortunately, long-term cultures in horse erythrocytes were unsuccessful, suggesting a host-specific restriction at some level.

Synthesis of Results and the Implications

• These results suggest that B. divergens is not host-specific at the level of cell attachment and invasion. It can infect erythrocytes from diverse hosts, suggesting a generalist infectious strategy.
• However, sustainable proliferation within the cell and survival appear to be significantly influenced once inside the host erythrocyte, indicating that intracellular factors may dictate the parasite’s viability.
• This research demystifies some of the host-parasite interaction dynamics of B. divergens, paving the way for potential vaccine development that does not rely on bovine materials, thereby increasing its safety and acceptability.