Eimeria nieschulzi infections in inbred and outbred rats: infective dose, route of infection, and host resistance

Abstract

Some of the host–parasite interrelationships between Eimeria nieschulzi (Protozoa: Sporozoa) and inbred and outbred strains of rats, were analyzed. The sex of the host did not influence the severity of infection; however, starved rats as compared with fed ones produced significantly lower numbers of oocysts during an infection. Mechanical crushing of infected faeces yielded a significantly higher number of oocysts than those crushed manually. The reproductive potential of the parasite varied inversely with the dosage of oocysts. Infections were caused by parenteral injections of sporozoites through four routes. In every case these inoculations caused milder infections than those elicited by similar doses of oocysts or sporozoites given orally. All infections stimulated resistance in rats; the intensity of this immunity was dose dependent. Single doses of 2500 and 3500 oocysts or more induced total resistance in outbred and inbred rats, respectively. This immunity was demonstrated 15 days after inoculation, by challenge infections. No developing stages were found in the intestinal tissues of rats which were immunized and then challenged.