IDENTIFICATION OF SURROGATE RODENT HOSTS FOR LARVAL ONCHOCERCA-LIENALIS AND INDUCTION OF PROTECTIVE IMMUNITY IN A MODEL SYSTEM

The objectives of this project were to screen a variety of inbred rodent species and strains to determine their usefulness as surrogate hosts for the study of the early larval development of Onchocerca lienalis and then to use a selected model to study the induction of protective immunity. In the primary screen, 6 strains of mice, 5 strains of rats, jirds, and multimammate rats were tested. Animals were infected with fresh O. lienalis by subcutaneous implantation of third-stage larvae (L3) contained in diffusion chambers covered with 5.0-mu-m pore-size membranes. After 7 days the chambers were recovered, and larval viability and growth were assessed. Approximately one-half of inoculated larvae were recovered alive regardless of the host tested. Larvae were implanted in CBA/J and DBA/2J mice in chambers covered with membranes that prevented host cells from entering; survival and growth rates of the larvae were not altered by the absence of cells from the chambers. Cryopreserved larvae were implanted in chambers with 5.0-mu-m pore-size membranes in CBA/J and DBA/2J mice and Wistar Furth rats for 3-28 days. No statistically significant difference was seen in the larval recoveries on days 3-28 in all 3 hosts. Statistically significant increases in length were seen in the 3 strains from day 3 to day 14, after which growth appeared to cease. Molting from L, to fourth-stage larvae was observed in all 3 hosts beginning on day 3, with most larvae completing the molt by day 7. No difference in growth or molt rates was detected between fresh and cryopreserved L3. DBA/2J mice were inoculated with L3 irradiated with 0-75 krad to determine whether they would develop protective immunity. Statistically significant reductions in parasite survival were seen in mice immunized with irradiated larvae regardless of irradiation dose. These experiments have demonstrated that inbred strains of mice and rats will support early growth and development of 0. lienalis larvae. Furthermore, the results have shown that these rodent models will be valuable for the study of the immunobiology of Onchocerca spp. infections.