Dr. Murai Éva szerk.: Parasitologia Hungarica 12. (Budapest, 1979)

Results Susceptibility of Mastomys natalensis to primary infection In Exp. 1 groups of Mastomys males or females were infected by 500, 1000 or 2000 larvae, and on day 6 the number of adult Nippostrongylus was determined. A group of rats, each infected with 1000 larvae was set up as control (Table 1). At post mortem examination sexually mature worms were found in each Mastomys exposed to infection. Males and females did not notably differ in respect of susceptibility. Of 500, 1000 and 2000 larvae on average 20.4, 37.9 and 44.9%, respectively, developed to maturity in the Mastomys hosts, less than that in the rats (46. 1%). Table 1 Worm recoveries in male and female Mastomys natalensis 6 days after larval Nippostrongylus brasiliensis infection Host animals Larval dose Worm recoveries Species I Sex No. Larval dose Mean worm counts (ranges) % take Mastomys female 5 500 95. 4 ( 54 - 127) 19. 0 20. 4 1

1 male 13 500 108. 6 ( 84 - 187) 21.0 20. 4 1

1 female 3 1000 332. 3 (177 - 561) 33. 2 37. 9 " male 13 1000 389. 9 (236 - 538) 38. 9 37. 9 11 female 6 2000 836. 0 (623 - 1149) 41.8 44. 9 " male 11 2000 933. 0 (459 - 1434) 46. 6 44. 9 Rat female 5 1000 461. 0 (365 - 525) 46. 1 46. 1 Localization in th

e small intestine Five female and 13 male multimammate rats infected with 500 larvae (Exp, 1) were examined for the localization of the parasite in the gut 6 days after infection. Mean worm counts registered in each of eight 5 cm long segments of small intestine are shown in Fig. 1. Most worms (66.8%) were located in the anterior half of the gut, however, considerable number of worms was present also in the distal ileum. Dynamics of egg output The characteristics of egg output of infected Mastomys and rats were compared in two experiments (Fig. 2). In Exp. 2 7 rats and 16 Mastomys, in Exp. 3 10 rats and 19 Mastomys were infected with 500 larvae, and EPG was assessed at 1-3-day intervals. The group mean egg counts calculated from individual EPG values are shown in Fig. 2. The graphical presentation indicates that rats and Mastomys began to pass eggs on day 5 and 6 after infection, respectively maximum egg output being reached on day 7 in both species. The Mastomys hosts discharged conspicuously less eggs (max. 1 000 EPG) than the rats (max. 8 000-18 000 EPG). In rats there is a gradual decline of egg discharge until its