An in vitro method is described where shells of Echinococcus granulosus ova are removed and the free oncospheres are activated to assess viability.
The hatching and activating effects of several digestive enzymes on the ova of E. granulosus, obtained from experimentally infected dogs, were tested. Ova and hatching-activating solutions were mixed in glass tubes and incubated in a water bath at 37°C. At 30-minute intervals 2 drops was placed on a slide, and all unhatched eggs, motile oncospheres and nonmotile oncospheres were counted.
The egg shells of E. granulosus remained intact in distilled water and physiological saline at 37°C for at least 48 hours. Acid pepsin did not seem to have any effect on the dissolution of the shells or on the activation of the free oncospheres. Both NaHCO3 and NH4OH removed shells without activation of oncospheres. Pancreatin and trypsin caused some activation of the free oncospheres. Bile, bile salts and cholesterol all enhanced the activating effects of pancreatin and trypsin; but whole bile was a more effective synergist than the individual bile salts tested.
Evidence from preliminary experiments suggests that oncospheres recovered from attached proglottids, being less mature, are activated at a lower rate.