Assessment of viability of Schistosoma mansoni miracidia by Congo red staining

The viability of Schistosoma mansoni miracidia, either hatched or unhatched, has been assessed by a staining technique using Congo red, a pH-sensitive dye (pH 3-5), under the light microscope. Hatched, free-swimming miracidia and live miracidia inside egg shells were stained light blue whereas dying miracidia altered the dye color from blue to orange and eventually to red. Immature eggs containing undeveloped miracidia were not stained by Congo red. This staining technique is simple, rapid and can be used as a method to assess both the viability of S. mansoni miracidia and the hatching process.