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

almost complete cessation by day 14-18. In the Mastomys hosts there is a more rapid fall of faecal egg counts and from day 8-9 eggs are only sporadically passed in the faeces. In 10 and 10 multimammate rats killed on days 20 and 22 in Exps. 2 and 3, respectively, no worms could be detected at all. In contrast, 7 and 10 rats of the respective experiment still harboured a mean residual population of 0.7 and 49.9 worms, respectively. Fig. 1: Intestinal localisation of worms in Mastomys natalensis on day (i after infection with 500 Nippostrongylus brasiliensis larvae (n T 18) Rejection of the primary worm population In Exp. 4 18 rats and 17 Mastomys were infected with 500 larvae each. On days 6, 8, 9, 12, 14 and 15 after infection 3 or 4 animals were killed in both groups to assess the current worm burden (Table 2). While worm counts in rats began to show considerable decline only from day 14 onwards, in the Mastomys a substantial reduction of the worm burden has already become apparent by days 8-9. Secondary infection Another experiment was also performed in order to demonstrate whether- multimammate rats infected with Nippostrongy

les will develop acquired resistance to secondary infection (Exp. 5). Twelwe female rats and six each of Mastomys males and females were infected with 500 larvae. Fifteen days later residual worm burden was removed by 200 mg/kg oral dose of thiabendazole. Two days later each animal was given a secondary infection of 500 larvae together with five previously not infected animals of both species to serve as controls. Six