The Effects of Trypanosoma lewisi on the Development of Hymenolepis diminuta in Concurrently Infected White Rats

Abstract

The effects of infection with Trypanosoma lewisi on the simultaneous development of Hymenolepis diminuta in Sprague-Dawley rats was studied. The mean wet weight of H. diminuta was significantly less in heavily inoculated (7 X 106 trypanosomes) rats, than that of worms in more lightly inoculated (1 X 106 trypanosomes) rats. Worms in rats which received trypanosomes on the 8th day of the cestode infection weighed significantly less than worms in control rats. The weight of worms in rats receiving trypanosomes on the same day as the cestodes was not significantly different from that of worms in control rats. The recent review by Heyneman (1963) indicates the effect of prior and concurrent helminth infections on host-parasite interrelationships. Generally in such studies two parasites with similar habitats have been introduced simultaneously into a given host (Larsh and Donaldson, 1944; Holmes, 1957, 1961, 1962a, b; Read and Phifer, 1959). Yoeli (1956) used concurrent Plasmodium berghei-Schistosoma mansoni infections in voles to study the effects of a helminth on the course of a malarial infection in the host. Although he employed dissimilar parasites, the habitats of these organisms are similar. Ashley (1962) described three experiments which showed the effect of a concurrent infection with Trypanosoma lewisi on development and maintenance of acquired immunity to Nippostrongylus brasiliensis. N. brasiliensis is an intestinal parasite as an adult, and a tissueinhabiting organism during its migratory larval stage. Thus both animals in Ashley's experiments dwell in the tissues during a part of their life history. Heyneman (1962) selected two closely related helminths, Hymenolepis diminuta and Hymenolepis nana, to study helminth immunity. The immunogenic tissue phase of H. nana was inhibitory to the infectivity and growth of the nonimmunogenic H. diminuta, an inhabitant of the intestinal lumen. The lack of research on a possible interaction between dissimilar organisms whose habitats are widely separated in the same host stimulated the present work. Our experiments were designed to determine the effect of a strictly Received for publication 23 August 1965. * Present address: Department of Zoology, Utah State University, Logan, Utah. tissue-inhabiting parasite, Trypanosoma lewisi, on the development of a strictly intestinal helminth, Hymenolepis diminuta, when both parasites are found concurrently in the same host. MATERIALS AND METHODS Male Sprague-Dawley white rats from the Northwest Rodent Company, Pullman, Washington, were maintained on tap water and Purina Laboratory chow supplied ad lib. The rats were housed in pairs in wire cages and divided into five groups: (1) uninfected control; (2) trypanosome control; (3) simultaneous infection (both parasites given on day 1 of the experiment); (4) helminth infection administered on day 1, trypanosomes on day 8; (5) cestode control. Five to eight cysticercoids of the tapeworm, Hymenolepis diminuta, were obtained from infected beetles, Tenebrio molitor, and administered by means of a stomach tube to rats lightly anesthetized with ether. The stock of Trypanosoma lewisi was maintained in host rats by intraperitoneal injections of infected blood at 7-day intervals. The experiment was conducted in two series. Six-week-old rats of Series A received 7 X 106 trypanosomes per ml of diluting fluid. In Series B 7-week-old rats received 1 X 106 trypanosomes per ml. Since the two series were not conducted simultaneously, controls were used for each. In both series eight rats were used in each of the five groups (two exceptions), and rat body weights were determined daily throughout the experiments (Table I). The infected rat blood was diluted with a solution containing 2 g sodium citrate, 0.75 g sodium chloride, and 0.2 g glucose per 100 ml distilled water. The rats were infected by intraperitoneal injection of 1 ml of diluting fluid containing the appropriate number of trypanosomes. Homogeneity of the trypanosome distribution within the diluting medium was maintained according to the method of Lincicome and Francis (1961). One ml of parasite free diluent was administered to each uninfected control animal. Estimations of tail