ABSENCE OF PROTECTIVE RESISTANCE TO HOMOLOGOUS CHALLENGE INFECTIONS IN JIRDS WITH CHRONIC, AMICROFILAREMIC INFECTIONS OF BRUGIA-PAHANGI

Most jirds (Meriones unguiculatus) with chronic Brugia pahangi infecti ons remain microfilaremic, develop a hyporesponsive state, and are sus ceptible to reinfection. Although few, some jirds become amicrofilarem ic or fail to develop a microfilaremia. The hypothesis that chronicall y infected, amicrofilaremic jirds may be resistant to reinfection was tested. Twenty-four chronically infected amicrofilaremic jirds, with o r without circulating antigen, were inoculated subcutaneously with 75 B. pahangi third-stage larvae (L(3)). Necropsies were performed 25 day s postinoculation, and challenge populations were separated from exist ing worms by size. Similar inoculations and necropsies were performed on groups of chronically infected microfilaremic jirds and uninfected jirds. Based on worm recoveries, jirds with occult infections were not resistant to reinfection. An anamnestic antibody response to extracts of L(3) or microfilariae (mf) was not seen, nor were antibodies to th e surface of L(3) or mf. The data indicate that a susceptible state is maintained in this model of lymphatic filariasis in the absence of ci rculating mf.