Haplosporidian host:parasite interactions

Area of Science:

• Marine biology
• Parasitology
• Immunology

Background:

• Oysters are susceptible to serious haplosporidian pathogens, including Bonamia spp. and Haplosporidium nelsoni.
• Host-parasite interactions and haemocytic responses are crucial for understanding disease progression.
• Limited knowledge exists regarding oyster haematopoiesis, haemocyte identity, and development.

Purpose of the Study:

• To review host-parasite interactions of major oyster haplosporidian pathogens.
• To elucidate the haemocytic response mechanisms against these parasites.
• To highlight variations in haplosporidian life cycles and host-parasite dynamics.

Main Methods:

• Literature review of existing studies on Bonamia spp. and Haplosporidium nelsoni.
• Analysis of haemocytic responses, including phagocytosis, immune evasion strategies, and cellular reactions.
• Comparison of parasite strategies (extracellular vs. intracellular) and host defense mechanisms.

Main Results:

• Haplosporidium nelsoni and NZAP are extracellular parasites with large plasmodia.
• Bonamia spp. are intracellular parasites with small plasmodia that are phagocytosed by haemocytes.
• Host immune evasion involves blocking lysosomal enzymes, ROS, and potentially inducing apoptosis.
• Differences in host immune factors may explain varying susceptibility, as seen in Crassostrea gigas vs. Ostrea edulis.
• Lipid bodies (LBs) in host granulocytes and parasites suggest conserved roles in innate immunity and inflammation, potentially involving eicosanoid synthesis.

Conclusions:

• Haplosporidian parasites exhibit diverse strategies, impacting host immune responses differently.
• Understanding conserved mechanisms like lipid body function is vital for invertebrate immunology.
• Further research is needed to fully characterize haplosporidian diversity and their complex host interactions.