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 infections remain microfilaremic, develop a hyporesponsive state, and are susceptible to reinfection. Although few, some jirds become amicrofilaremic or fail to develop a microfilaremia. The hypothesis that chronically infected, amicrofilaremic jirds may be resistant to reinfection was tested. Twenty-four chronically infected amicrofilaremic jirds, with or without circulating antigen, were inoculated subcutaneously with 75 B. pahangi third-stage larvae (L3). Necropsies were performed 25 days postinoculation, and challenge populations were separated from existing 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 L3 or microfilariae (mf) was not seen, nor were antibodies to the surface of L3 or mf. The data indicate that a susceptible state is maintained in this model of lymphatic filariasis in the absence of circulating mf.