Immunological studies on the mechanism of resistance in experimental onchocerciasis

Human onchocerciasis is a debilitating disease, which causes lymphatic obstruction and gives rise to genital elephantiasis. The microfilariae also cause severe itching, while invasion of the eyes by large numbers, and the reaction to their presence, lead to river blindness. This results in severe medical, social and economic problems (Stevenson 1987).The implications of the disease bring about the need to control onchocerciasis by  understanding the mechanism of the host’s resistance. The aim of this study was to investigate the possibility of using laboratory rodents as models for immunological studies of onchocerciasis. Living adult Onchocerca (O.) armillata and O. volvulus were surgically transplanted into the peritoneal cavities of rats, after initial immunizations or transplantations, in order to investigate the survival rates of the transplanted parasites. Steroid administration significantly improved the survival rate of implanted O. armillata in rats at 60 days (X2 = 3, df =1, P<0.05). A similar effect was produced in O. volvulus with the survival rate being significantly higher than in rats not treated with cortisone (x2 = 6.3, df = 1, P <0.01). Immunization with extracts of O. volvulus and O. armillata or implantation of rats with live adult worms hindered the survival of homologous implants significantly, while no such effect was produced in heterologous implants. Immunization with microfilariae of either species of worms had no effect on the survival rate of subsequent implants of adult worms of the same species. Immunization with the peritoneal exudates, obtained from rats previously implanted with adult O. volvulus had a significant inhibitory effect on the survival of subsequently implanted adult O. volvulus (X2 =27, df = 1, P<. 001). The model is valuable for immunological and chemotherapeutic studies of the two species of Onchocerca.