Echinococcus granulosus in sheep: Transfer from ewe to lamb of ‘Arc 5’ antibodies and oncosphere-killing activity, but not protection

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Fourteen ewes were orally dosed with 2000 E. granulosus eggs at 2 weeks of age, were mated at 19 months, and produced lambs when the cysts were 2 years old. One week after parturition, all 14 ewes had ‘Arc 5’ antibodies in their serum, as did 11 14 of their lambs. Fourteen uninfected ewes were immunized three times before parturition with E. granulosus eggs injected intramuscularly. Cysts grew at the first, or first and second site, but not the third, indicating that the ewes were immune prior to parturition. Most sera from these ewes and their lambs, and from 14 control ewes and their lambs, produced precipitin arcs with hydatid cyst fluid, but no ‘Arc 5’. All lambs were challenged with 500 eggs 2 weeks after birth. At necropsy, cyst numbers within groups ranged from 3 to > 200, but there was no significant difference between the three groups of lambs. The immunized ewes did not pass a protection to their lambs that was effective when the lambs were challenged. ‘Arc 5’ antibodies were induced by prolonged infection with cysts, and were not seen in the sera of ewes immunized with eggs, although the eggs developed into cysts at the injection sites. ‘Arc 5’ antibodies did not protect lambs against infection, and were not correlated with protection in ewes. Subcutaneous injection of oncospheres into four ewes from each group at the time of lamb challenge showed that the immunized ewes were immune to this method of challenge, but the infected and control ewes were not. Ewes and lambs of the immunized group, and to a lesser extent the 2-year-infected group, had in vitro oncosphere-killing capacity in their serum collected 1 week after parturition, while those from the control group did not. Killing capacity in the sera of two hyperimmunized lambs was predominantly in the IgG2 subclass. It would appear that the IgG1 subclass, which is the major immunoglobulin in ewe colostrum, either does not carry protective antibodies, or is not able to participate in killing oncospheres in vivo in young lambs.