Schistosoma species: Transmission electron microscopy of the circumoval immune precipitin reaction on eggs

Eggs of Schistosoma mansoni, Schistosoma japonicum, Schistosoma haematobium, and Schistosoma mekongi incubated in serum from infected animals or humans had characteristic circumoval precipitin reaction products. When studied by transmission electron microscopy, these reaction products were seen in all species associated with egg shell pores from which antigen emerges. Reaction products were of variable density and sometimes were similar to long “septate” reaction products seen with light microscopy. No limiting membrane was seen around the reaction products. No true septa were seen. It is probable that the reaction product emerged from shell pores and was added to emerging material in spurts giving the septate appearance. No control eggs fixed immediately or first incubated in either saline or serum of uninfected controls showed characteristic reaction products.