STRONGYLOIDES-STERCORALIS - MAINTENANCE OF EXCEEDINGLY CHRONIC INFECTIONS

Two hypotheses were tested to identify the mechanism(s) by which chron ic Strongyloides stercoralis infections are maintained in experimental dogs as a model to explain delayed onset recrudescence in humans. Inv estigations tested the hypotheses that chronic infections result from 1) periodic reactivation of third-stage larvae from a reservoir of dor mant parasites outside the gastrointestinal tract or 2) the periodic r ejuvenation of postreproductive female worms remaining from a previous infection, lodged in the mucosal crypts. Populations of parenteral la rvae survived in mature experimentally infected female dogs for 66 day s; individual worms survived for ss days, but there was no evidence th at these larvae re-established patent, adult worm infections. Late in these infections, female worms were present in greater than predicted numbers with no evidence that autoinfection had occurred, suggesting t hat some postreproductive worms were long-lived. In separate trials, l ong-lived spent females were once again capable of producing viable la rvae when the host was treated with corticosteroids.