Development of Age and Sex Resistance to Nematospiroides dubius in the Mouse Following Single and Multiple Infections

Abstract

Groups of 6to 8-week-old male and female S-W mice were immunized with 3 spaced oral doses of 50 Nematospiroides dubius infective larvae at 14-day intervals. Fourteen days after the third infection, animals were treated with pyrantel tartrate to remove worms of the 3 stimulating infections. Ten weeks after drug treatment, designated groups of animals were challenged (per os) with 50 N. dubius infective larvae each. Similar groups were challenged at 20, 30, 40, and 50 weeks after drug treatment. Adult worm counts 14 days after challenge indicated that in both male and female mice immunity persisted for at least 50 weeks when compared with nonimmunized controls. Although this protection decreased over the 50-week period in males, females maintained a striking degree of protection over this same 50-week period. Furthermore, there was no apparent difference in the number of adult worms recovered from the aging experimental animals over the 50-week period when compared with age-resistance controls given a corresponding single infection of 50 N. dubius larvae. Hence, in the strain of animals used in this study the results indicated that neither age nor sex resistance was evident after a single oral infection with 50 N. dubius larvae. Dobson (1961, 1962) reported that following a single oral infection with 50 N. dubius larvae, both immature and mature male Swiss mice harbored more worms than females, and age resistance to this parasite was observed in both male and female mice following a single oral infection. Van Zandt (1961) reported that S-W mice, given three spaced oral stimulating doses of 50 N. dubius infective larvae, showed a significant reduction of worms after an oral challenge with 50 N. dubius infective larvae given 21 days after the third stimulating infection. The purpose of this experiment was to determine the effect of the host's sex and age on the expression of immunity to this parasite in mice immunized by oral infections. MATERIALS AND METHODS Forty male and 40 female S-W mice 6 to 8 weeks old were randomly distributed into 10 groups of 8 mice each, 4 males and 4 females per group. Hence, 40 mice comprised experimental groups E-I, E-II, E-III, E-IV, and E-V while the remaining 40 animals were used as control groups C-I, C-II, C-III, C-IV, and C-V. In Received for publication 14 May 1973. * This work was supported by NIH Grant AI10490-02. t Department of Biological Sciences, Youngstown State University, Youngstown, Ohio 44503. t Department of Epidemiology and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15213. addition, 5 groups of 8to 12-week-old mice, 4 males and 4 females per group, were utilized as age-resistance controls AR-I, AR-II, AR-III, AR-IV, and AR-V. The animals of the 5 experimental groups (E-I to E-V) were given 3 stimulating oral infections with 50 N. dubius larvae each at 14-day intervals. Fourteen and 16 days after the third stimulating infection, each animal of the 5 experimental groups received an oral dose of pyrantel tartrate (60 mg/kg of body weight) (Cypess and Van Zandt, 1973). Ten weeks after the last drug treatment, the mice of experimental group E-I and control groups C-I and AR-I were given a challenging infection of 50 N. dubius larvae. Fourteen days after challenge, the mice of all 3 groups were killed and the adult N. dubius recovered from the small intestines were counted. The mice of the remaining groups were handled as above, except that groups E-II, C-II, and AR-II were challenged 20 weeks after drug treatment, groups E-III, C-III, and AR-III at 30 weeks, E-IV, C-IV, and AR-IV at 40, and E-V, C-V, and AR-V at 50 weeks. Immunity is recorded as a per cent of protection and followed the model of Rubin et al. (1971).