Anthelmintic activity of acetone-water extracts against Haemonchus contortus eggs: Interactions between tannins and other plant secondary compounds

- Acetone-water extracts of Lysiloma latisiliquum, Laguncularia racemosa, Rhizophora mangle, Avicenna germinans and Theobroma cacao (seed husk and pulp) affected Haemonchus contortus egg hatching mainly by blocking eclosion of larvae from eggs, although a minor ovicidal effect was also recorded for T. cacao extracts.
- The pre-incubation of extracts with PVPP to block tannins and other polyphenols indicated that polyphenols were not responsible for blocking larvae eclosion, with the exception of the L. racemosa extract.
- Addition of PVPP suggested unfavorable interactions between polyphenols and other PSC contained in the extracts, which significantly limited the AH effects on eggs.

This study aimed at (i) describing the effects of acetone-water extracts obtained from a range of different plant materials, on the hatching process of Haemonchus contortus eggs under in vitro conditions and (ii) identifying the role of tannins and other plant secondary compounds (PSC), on these AH effects by using polyvinylpolypyrrolidone (PVPP), an inhibitor of tannins and other polyphenols. An egg hatch assay (EHA) was used to determine the AH effect. Acetone-water (70:30) extracts from different foliages (Lysiloma latisiliquum, Laguncularia racemosa, Rizophora mangle, Avicennia germinans) and plant by-products (Theobroma cacao seed husk and pulp, and percolated Coffea arabica) were obtained. Fresh H. contortus eggs were incubated in PBS with increasing concentrations of each extract (0, 600, 1200, 2400 and 3600 μg/ml PBS). A general linear model was used to determine the dose effect of each extract. A mild ovicidal activity was only recorded for T. cacao extracts (seed husk and pulp). The main anthelmintic (AH) effect for all the extracts, except for C. arabica, was to block the eclosion of larvated eggs. The use of PVPP at 3600 μg/ml PBS showed that tannins of the L. racemosa extract were responsible for blocking eclosion of larvated eggs. Extracts of L. latisiliquum, A. germinans, T. cacao seed husk and pulp also blocked eclosion of larvated eggs but the addition of PVPP indicated that tannins were not responsible for that activity. In contrast, it suggested unfavorable interactions between polyphenols and other PSC contained in those extracts, limiting the AH effect on the egg hatching process. The present results suggest that the interactions between tannins and other PSC are complex and may reduce the AH effects against H. contortus eggs.