EXPERIMENTAL OESOPHAGOSTOMUM-DENTATUM INFECTION IN THE PIG - WORM POPULATIONS RESULTING FROM SINGLE INFECTIONS WITH 3 DOSES OF LARVAE

This report describes the effect of different dose levels of infection upon worm burdens and development and fecundity of the parasites. Thr ee groups each of 40, 9-weeks-old, helminth naive pigs were inoculated once with either 2000 (group A), 20,000 (group B), or 200,000 (group C) infective third stage larvae of Oesophagostomum dentatum. Subgroups of 5 pigs from each major group were killed 3, 6, 11, 14, 18, 25, 34 and 47 days post inoculation (p.i.) and the large intestinal worm burd ens were determined. Faecal egg counts were determined at frequent int ervals after day 13 p.i. There were no overt clinical signs of gastroi ntestinal helminthosis during the experiment. Faecal egg counts became positive in groups A and B at around day 19 p.i., whereas most pigs i n the high dose group C did not have positive egg counts until day 27- 33 p.i. and some pigs remained with zero egg counts until the end of t he study. Throughout the experiment the worm populations in group C co nsisted mainly of immature larval stages, while those in groups A and B were predominantly adult stages after days 14-18. Adult worms from t he low dose group A were significantly longer than these from group C. At high population densities, stunted development of worms and reduce d fecundity among female worms were found. Furthermore, there was a te ndency for the distribution of the worms within the intestine to be al tered with increasing population size.