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Host-Parasite Relationships in Echinococcosis

VII. Resistance of the Ova of Echinococcus granulosus to Germicides^*

The resistance of Echinococcus granulosus eggs to several germicides was determined by comparing their hatching and activation rates to those of unexposed controls.

Five per cent sodium hypochlorite caused prompt dissolution of the egg shells, but 31 to 42% of the oncospheres were viable after 90 minutes exposure. In 1 to 2% Tide®, almost all oncospheres hatched; up to 63% of the oncospheres were living after 24 hours, but 6 hours exposure to a 5% solution dissolved all eggs. Roccal® reduced the hatching rate slightly; up to 11% of the oncospheres were living after 30 minutes exposure to concentrations of 1,000 ppm; and an occasional oncosphere survived concentrations of up to 2,000 ppm for 30 minutes. Hatching rates were decreased after long exposure to 70 and 95% ethyl alcohol; 20 to 30% of the hatched oncospheres were viable after 60 minutes. Lysol® solutions reduced hatching rates at higher concentrations, but up to 10% of the hatched oncospheres were living after 60 minutes exposure to a 10% solution; some oncospheres survived a 20% concentration for 30 minutes. The effect of 5 to 20% formalin was to fix the shells and prevent hatching; when shells were artificially removed with 1% sodium hypochlorite the oncospheres were found to survive exposure to 20% formalin for 24 hours.

^* Aided by research grants from the National Institute of Allergy and Infectious Diseases, U.S.P.H.S. (E-2205) and the World Health Organization. A preliminary report of this work appeared in the Proceedings of the VIIth International Congress on Hydatid Disease (1960), Rome.