Nippostrongylus brasiliensis was serially passed in mice for over 30 consecutive generations. Periodically during this work comparisons were made of the ability of the mouse-passed population and the original rat strain of the parasite to develop in both rats and mice. Mouse passage was found to significantly enhance the ability of the parasite to develop in mice after four mouse passages, and to significantly decrease the ability of the parasite to develop in rats after eight mouse passages. The natural host of Nippostrongylus brasiliensis (Travassos, 1914) is the Norway or brown rat (Haley, 1961). Experimental infections with this nematode have been produced in mice by a number of investigators (Brackett and Bliznick, 1949; Neafie and Haley, 1962; and Porter, 1935), and Porter (1935) has compared the development of this parasite in rat and mouse hosts. In investigations (Wescott, 1964, and Wescott and Todd, 1964) at our laboratory, N. brasiliensis infections have been produced in mice with little difficulty, but frequently the numbers of adult worms developing in these infections were erratic and unpredictable, which detracted from the value of the use of this parasite in mice. To alleviate the problem of uncertain development of N. brasiliensis in mice, an attempt was made to establish a population of this parasite by serial passage in mice that would grow more successfully in mice than the parent rat strain. Over a 2-year period N. brasiliensis was passed in mice for over 30 consecutive generations and periodic comparisons were made of the mouse-passed population and the original rat strain. These comparisons are presented in this paper in the form of a chronological study of the ability of the mouse-passed population and the parent rat strain to develop in both mice and rats. Received for publication 19 July 1965. * From the Department of Veterinary Science, University of Wisconsin, Madison, paper NS 476. This investigation was supported in part by a Public Health Service Fellowship (EPD-15,937) from the NIAID, Public Health Service; in part by a Public Health Service Research Grant (AI06452-01); and in part by the American Cancer Society Institutional Research Grant to the University of Wisconsin. t Present address: School of Veterinary Medicine, University of Missouri, Columbia, Missouri. MATERIALS AND METHODS The host animals used throughout this work were ARS/ICR 5-week-old male mice and ARS random bred 5-week-old male rats supplied by a local commercial laboratory animal producer (A. R. Schmidt, Co., Madison, Wisc.). These animals were maintained in wire bottom cages in this laboratory and had free access to feed and water at all times. Routinely one cage of six to eight mice was used each week for serial passage of the parasite in mice, and one cage of four to six rats was used every 2 weeks to passage and maintain the original rat population. Once animals had been used for these purposes they were destroyed and not used for subsequent passages. The strain of N. brasiliensis used was a standard rat strain supplied by Dr. A. James Haley, University of Maryland, several months prior to the beginning of this work. For the first mouse passage eight mice were each injected subcutaneously with about 1,000 8-day-old rat strain N. brasiliensis larvae. Thereafter, the feces were collected daily from the 6th to the 9th day after exposure, mixed with granular bone charcoal, moistened, and incubated at room temperature. Seven days after the last culture was made the larvae were removed from these cultures with the Baermann apparatus and pooled. Since the number of larvae obtained was not adequate to infect another group of mice, additional larvae of rat origin were added to the inoculum for the second passage. Eight mice were then injected with the mixed larval suspension, each receiving approximately 25 larvae of mouse origin and 275 larvae of rat origin. Cultures were made of their fecal material as before and these cultures as well as cultures in subsequent passages contained enough larvae so that larvae of rat origin were not used again. After the second mouse passage the parasite was routinely passed in mice by injecting six to eight mice each with 200 to 400 7to 14-day-old larvae. The procedures used to maintain the original rat strain of the parasite in rats were the same as used in previous work (Wescott and Todd, 1964). The percentage of larvae of mouse origin that developed to adult worms in mice and rats was determined periodically during this work, and in some instances this development was compared to the development of rat origin larvae in similar hosts. When such comparisons were made, the larval inocula used were prepared similarly using larvae of the same age from the two populations
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Dec 1, 1993
Isabel Gaytan‐Mondragon + 2
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