Background: Few studies concerning Biomphalaria alexandrina (B. alexandrina) snail hemocytes'
subpopulations, and their relation to the compatibility with Schistosoma mansoni (S. mansoni)' miracidia
were performed. Manipulation of parasite development inside these snails could be applied as a control
measure against schistosomiasis.
Objectives: Knowing that the snail hemocytes temporarily bind to the parasites, allowing the development
of cercariae that are infective to the definitive host. This study aimed at studying the morphology and
kinetics of diverse hemocytes of susceptible and resistant B. alexandrina and their participation in the
snail early immune response after challenge by S. mansoni.
Material and Methods: Giemsa stained hemocytes were characterized using light microscopy. Total and
differential hemocyte counts (THC and DHC) were calculated in the hemolymph of two groups composed
of 60 susceptible and 60 resistant snails. Each group was further subdivided as 12 control pre-exposure
snails (PE) and 48 post-exposure snails (PO) to S. mansoni at different time points (6 h, 1, 3 and 7 days).
THC and DHC counts were recorded by a snail hemogram.
Results: Results revealed that granulocytes constituted the most common population all through the
experiment with the large dense-granulated granulocytes subpopulation being the largest-sized cells
detected. The highly reactive subpopulations that increased in number upon exposure to S. mansoni were
the few-granulated and the large-granulated granulocytes, suggesting their possible participation in early
parasite destruction.
Conclusion: The resulting hemograms helped determine the participation of hemocyte populations and
subpopulations in the defense against S. mansoni, aiding in understanding snail compatibility patterns.
Further studies to propagate transgenic B. alexandrina snails abundant in large granular granulocytes
utilizing (gene editing) CRISPR-Cas9 technique are recommended. This would be required to spread
schistosome resistance traits in snail populations, thus, contributing to reduced schistosomiasis
transmission in the long run.