Resistance and disease in Brugia malayi infection of ferrets following prior infection, injection of attenuated infective larvae and injections of larval extracts.

A partial resistance expressed by a 53% to 78% reduction in lymphatic filariae from a challenge infection was induced in ferrets (Mustela putorius furo) by a prior infection and by injection of radiation attenuated infective larvae (L3) but not by injections of lyophilized microfilariae (mf) or L3. Equivalent acquired resistance was demonstrated with and without overt filarial disease. A prior infection resulted in peripheral lymphoedema in approximately one-third of the amicrofilaraemic resistant ferrets following challenge infection and injection of attenuated larvae resulted in inflammatory responses characteristic of a hyper-responsive syndrome in one-half of the amicrofilaraemic ferrets. Injections of lyophilized mf inhibited microfilaraemia and promoted development of lymphostatic disease. A limited examination of immune responses and histopathology suggested that disease in partially resistant ferrets was associated with high TH2 dependent responses directed, at least in part, to mature filariae and to mf. Mechanisms of resistance were not identified.