Exposure of sows to Ascaris suum influences worm burden distributions in experimentally infected suckling piglets

This paper reports on the influence of maternal exposure to Ascaris suum on worm burden distributions in experimentally infected piglets. In the first study, sows were inoculated before and during gestation (6 months, long-te rm exposure) with 10000 A. suum eggs twice weekly. In a second study, sows were inoculated during gestation only (3 months, short-term exposure) with increasing doses of eggs (10 000-40 000 eggs twice weekly). Helminth-naive sows served as controls in both studies. The third study used the same desi gn as the short-term exposure study, but piglets from exposed and control s ows were cross-suckled within 4 h of birth before colostrum uptake. All pig lets were inoculated 2 or 3 times with 50 A. suum eggs on days 4 and 7 (and 14) after birth, and left with the sows. At 10 weeks of age all piglets we re necropsied, and liver lesions and worm burdens were recorded. Surprising ly, in piglets born to long-term exposed sows, the prevalence of A. suum in fection and the mean worm burden were significantly higher than those in pi glets from control sows. In contrast, neither worm burdens nor prevalence w ere significantly different between piglets from short-term exposed sows co mpared with their controls. In the cross-suckling experiment, 67 % of pigle ts suckling control sows harboured worms at slaughter, compared with 15 % o f piglets suckling exposed sows. Maximum likelihood analysis of worm burden distribution and the degree of parasite aggregation showed 3 distinctly di fferent types of overdispersed distributions: worm counts in piglets from c ontrol sows, in piglets from short-term exposed sows and in piglets from lo ng-term exposed sows. When the worm burden data were analysed including the cross-suckled piglets by biological mother, it appeared that the control a nd short-term distributions converged and that only the long-term exposure was significantly different. Overall, the degree of parasite aggregation in piglets infected with A. suum decreased with exposure of the sows. A non-l inear relationship was observed between prevalence of infection and mean wo rm burden, which was different for piglets from exposed and control sows, a nd similar to relationships of this type that previously have been found in human A. lumbricoides infections. It was concluded that in porcine,4. suum infections maternal exposure alters the distribution of worms in their off spring, in which the duration of exposure appeared to be an important influ ence. The results of the cross-suckling further suggest that maternal facto rs, e.g. antibodies, are transferred via colostrum.