Development, hatching, and infectivity of Echinostoma caproni (Trematoda) eggs, and histologic and histochemical observations on the miracidia.

Light microscopy studies were done on the eggs and miracidia of the intestinal trematode Echinostoma caproni. Eggs were obtained by homogenizing adult worms derived from ICR mice in artificial spring water (ASW). To study egg development and to obtain miracidia, eggs were incubated in ASW in either a light or a dark environment for 10 days at 28 degrees C. Egg development was characterized and staged at 2-day intervals from day 0 to day 10 postembryonation. No significant difference in development was seen in eggs maintained under conditions of light or darkness. Eggs maintained in darkness for 10 days and exposed to incandescent light produced a large synchronous hatch of miracidia within 3 h of exposure to light. As expected, miracidia used to expose Biomphalaria glabrata snails produced patent infections at 5-7 weeks postinfection (p.i.). Embryonated eggs aged from 0 to 10 days that had been fed to B. glabrata snails also produced infections within 4 weeks of infection. Miracidial longevity studies showed that 50 newly hatched miracidia maintained at either 4 degrees, 12 degrees, 22 degrees, or 38 degrees C lived for 6, 28, 14, and 5 h, respectively. Histology studies were done on whole miracidia stained in 0.01% neutral red and in Schneider's acetocarmine. Histochemistry studies of miracidia stained with alcian blue (pH 2.5) showed the presence of acid mucopolysaccharides in the epidermal plates; miracidia treated with periodic acid-Schiff plus 0.5% malt diastase showed the presence of glycogen in the body and in the epidermal/subepidermal region. Miracidia stained with Lillie's Oil Red O showed the presence of sparse neutral fat droplets in the body.