Assessment of the anthelmintic activity of medicinal plant extracts and purified condensed tannins against free-living and parasitic stages of Oesophagostomum dentatum.

BACKGROUND: Plant-derived condensed tannins (CT) show promise as a complementary option to treat gastrointestinal helminth infections, thus reducing reliance on synthetic anthelmintic drugs. Most studies on the anthelmintic effects of CT have been conducted on parasites of ruminant livestock. Oesophagostomum dentatum is an economically important parasite of pigs, as well as serving as a useful laboratory model of helminth parasites due to the ability to culture it in vitro for long periods through several life-cycle stages. Here, we investigated the anthelmintic effects of CT on multiple life cycle stages of O. dentatum. METHODS: Extracts and purified fractions were prepared from five plants containing CT and analysed by HPLC-MS. Anthelmintic activity was assessed at five different stages of the O. dentatum life cycle; the development of eggs to infective third-stage larvae (L3), the parasitic L3 stage, the moult from L3 to fourth-stage larvae (L4), the L4 stage and the adult stage. RESULTS: Free-living larvae of O. dentatum were highly susceptible to all five plant extracts. In contrast, only two of the five extracts had activity against L3, as evidenced by migration inhibition assays, whilst three of the five extracts inhibited the moulting of L3 to L4. All five extracts reduced the motility of L4, and the motility of adult worms exposed to a CT-rich extract derived from hazelnut skins was strongly inhibited, with electron microscopy demonstrating direct damage to the worm cuticle and hypodermis. Purified CT fractions retained anthelmintic activity, and depletion of CT from extracts by pre-incubation in polyvinylpolypyrrolidone removed anthelmintic effects, strongly suggesting CT as the active molecules. CONCLUSIONS: These results suggest that CT may have promise as an alternative parasite control option for O. dentatum in pigs, particularly against adult stages. Moreover, our results demonstrate a varied susceptibility of different life-cycle stages of the same parasite to CT, which may offer an insight into the anthelmintic mechanisms of these commonly found plant compounds.

Effects of short-chain fatty acids and lactic acids on survival of Oesophagostomum dentatum in pigs.

The direct influence of intracaecal infusion of short-chain fatty acids (SCFA) and lactic acids (LA) on already established Oesophagostomum dentatum infection in cannulated pigs was investigated. We tested the hypothesis that the previously discovered anti-parasitic effect of inulin is mediated through its metabolic products SCFA and LA by infusing into cannulated pigs these compounds in amounts approximating to those produced in the pigs large intestine and caecum during the metabolism of inulin. The experiment comprised of 18 pigs--2 groups of 9 pigs in each. The normal diet used in the experiment was based on barley flour with insoluble fibre from oat husk with added soybean meal, vitamins and minerals. After 2 weeks of adaptation to the diet all the pigs were inoculated with 6,000 infective larvae of O. dentatum. Six weeks later, surgery on all pigs was performed to install cannulas into caeci. At 7 weeks post-infection (p.i.) the SCFA and LA infusion was initiated in Group 1 (experimental) pigs; at the same time pigs in Group 2 (controls) were infused with saline. At week 10 p.i., all pigs were killed and their worm burdens determined. SCFA and LA infused pigs exhibited markedly reduced fecal egg counts and worm recoveries (98 and 92% reduction, respectively, compared to saline controls). The results from this study demonstrate that SCFA and LA have a significant negative influence on established O. dentatum infection in growing pigs. The results also show that the type of dietary carbohydrates fed and its intestinal degradation can yield metabolic by products that profoundly influence helminth survival.