Susceptibility of ten Haemonchus contortus isolates from different geographical origins towards acetone:water extracts of polyphenol-rich plants. Part 2: Infective L3 larvae

This study explored the variation in susceptibility to acetone:water plant extracts between infective larvae (L-3) of ten Haemonchus contortus isolates from different geographical origin. The L-3 of 10 different isolates were exposed either to the acetone:water extract of a temperate plant (Onobrychis viciifolia) or a tropical plant (Acacia pennatula) and were evaluated with the larval exsheathment inhibition assay (LEIA). The L-3 of each isolate were incubated with different concentrations of each extract (0, 25, 50, 100, 200, 400, 600, 800, 1000 and 1200 mu g/mL of phosphate buffered saline (PBS)). After incubation, the exsheathment process of L-3 was induced using a solution with sodium hypochlorite (2%) and sodium chloride (16.5%). The proportion of exsheathed L-3 was determined for each concentration at 0, 20, 40 and 60 min. Effective concentrations 50% (EC50) and the corresponding 95% confidence intervals (95% CI) were calculated for every isolate with both extracts. Moreover, a resistance ratio (RR) was calculated for each extract to compare isolates, using the most susceptible isolate as the respective reference for each extract. To determine the role of polyphenols on the reported effect, a second set of incubations was made for each isolate and each extract, using the extracts at a concentration of 1200 mu g/mL PBS with or without polyvinylpolypyrrolidone (PVPP), a polyphenol blocking agent, and controls without extract. The ten different H. contortus isolates showed variation in susceptibility for each of the 2 extracts tested (P < 0.05). The EC50 values for A. pennatula extract ranged from 36 to 501 mu g/mL (RR: 2.11-13.68). Meanwhile, the EC50 values for O. viciifolia extract ranged from 128 to 1003 mu g/mL (RR: 1.25-7.82). The use of PVPP revealed that polyphenols were responsible for the anthelmintic activity recorded for both extracts. However, tested H. contortus isolates suggested that susceptibility to one polyphenol-rich extract did not determine the susceptibility to the other polyphenol rich extract. The latter result indicated that the different H. contortus isolates varied in their susceptibility to the polyphenols present in each extract evaluated.