BARREN FEMALE STRONGYLOIDES-STERCORALIS FROM OCCULT CHRONIC INFECTIONS ARE REJUVENATED BY TRANSFER TO PARASITE-NAIVE RECIPIENT HOSTS AND GIVE RISE TO AN AUTOINFECTIVE BURST

It is widely assumed that barren Strongyloides stercoralis occurring i n chronically infected carriers can become fecund when immunity wanes. Evidence for this involves corticosteroid treatment of hosts harborin g occult infections that subsequently return to patency. However, nema todes have ecdysteroid receptors, and it has been suggested that corti costeroids act directly on the parasite, inducing autoinfective develo pment, rather than indirectly by suppressing host immunity. To test th ese competing concepts, barren females were recovered from donor dogs when the dogs' fecal examinations turned negative. Groups of 100 activ e barren worms were surgically transplanted into the small intestines of each of 6 naive canine recipients. Three were examined at necropsy at 4-5 days postinfection (PI), before autoinfection could amplify the number of successfully transferred parasites. The remaining recipient s were examined 21-22 days PI when, if autoinfection had occurred, the worm populations should have increased. At 4-5 days, gravid worms occ urred in each of the recipients (19 +/- 6 worms/dog). By 21-22 days, a remarkable population increase had occurred (522.6 +/- 296 worms/dog) . Worms from chronically infected donors were stunted, and electron mi croscopy revealed damage to the intestine and ovaries. Successfully tr ansplanted worms recovered at days 4-5 PI were ovigerous and less stun ted and showed repair of intestinal and ovarian tissues.