A Comparison of the Development of Nippostrongylus brasiliensis in Germ-Free and Conventional Mice

Abstract

Germ-free and conventional mice of similar age and sex were exposed to filariform larvae of Nippostrongylus brasiliensis treated with sodium hypochlorite and antibiotics in four experiments, and in one experiment to filariform larvae which had been given a series of sterile saline washes. In two experiments involving sodium hypochlorite-antibiotic-treated larvae the mice retained their bacteriafree status while contamination occurred with single bacterial species in each of the other three experiments. Fewer adult worms were subsequently recovered from the germ-free and monocontaminated mice than from the conventional controls in all five experiments, and in three experiments these differences were statistically significant. The number of larvae observed in lungs examined 48 hr and 8 days after infection was similar in the germ-free, monocontaminated, and conventional mice, which was interpreted to indicate that the migration of Nippostrongylus takes place similarly through the lungs of both types of hosts, but that a normal bacterial flora in the host can favorably influence the development of adult worms. The use of germ-free host animals to study host-parasite relationships, although a relatively new and little-used technique, is generally regarded as a useful system to investigate the ecology of parasitism. Phillips and Wolfe (1959), Newton et al. (1960), and Doll and Franker (1963) have used germ-free animals to study protozoan infections and Newton et al. (1959, 1962) have successfully produced helminth infections in germ-free mice and guinea pigs. These reports demonstrate the practicability of using gnotobiotic host animals and also indicate that the bacterial flora of the host may influence the development of parasites. The interest generated by these investigations, together with recent improvements in equipment (Trexler, 1959, 1963), decreasing the expense of experimentation with gnotobiotic Received for publication 20 June 1963. * From the Department of Veterinary Science, University of Wisconsin, Madison, paper NS389. This investigation was supported in part by a Public Health Service Fellowship (EPD-15,937) from the National Institute of Allergy and Infectious Diseases, Public Health Service, and in part by the American Cancer Society Institutional Research Grant to the University of Wisconsin. animals, brought about the use of these techniques in this laboratory. In initiating work with germ-free animals at the University of Wisconsin the development of Nippostrongylus brasiliensis (Travassos, 1914) in germ-free and conventional mice was studied to investigate the effect of the absence of a normal bacterial flora upon this hostparasite relationship. The particular system was chosen because germ-free mice were commercially available locally and N. brasiliensis, which has been studied extensively (Haley, 1961, 1962), appeared to be well suited for such experimentation. The in vitro studies of this parasite by Weinstein and Jones (1956, 1959) and the previous work with N. brasiliensis in germ-free guinea pigs by Newton et al. (1959) also made this system particularly attractive for these initial studies. MATERIALS AND METHODS Procurement and maintenance of animals The animals used were germ-free and conventional ARS/ICR strain random-bred albino mice and ARS strain random-bred albino rats, supplied by a local commercial laboratory animal producer (the A. R. Schmidt Co., Madison, Wis.). For each experiment the producer assembled 13 germ-free