Scanning electron microscopy of Haemonchus contortus exposed to tannin-rich plants under in vivo and in vitro conditions.

The structural changes induced in adult Haemonchus contortus after in vitro and in vivo contact with a tannin-rich (TR) plant, either tzalam (Lysiloma latisiliquum) or sainfoin (Onobrychis viciifolia), were assessed using scanning electron microscopy (SEM). All the worms used in the study were adult females. The Haemonchus adult worms were obtained from the abomasum of infected donor goats. Adult H. contortus were kept in contact with the extracts of TR plants for 24h for the in vitro assays and were compared to worms maintained in PBS (control). For the in vivo studies, the adult H. contortus parasites were obtained from artificially infected goats. All the goats were fed a tannin-free diet until D27 post-infection when infection was patent. On D28 some goats were fed fodder of one of the TR plants for seven consecutive days. Thus, their H. contortus were in contact with TR fodder within the gastrointestinal tract. The control worms were obtained from goats fed only a tannin-free diet. In the in vitro assays and in vivo studies, the SEM observations revealed structural alterations in the worms after contact with TR plants when compared to the control worms (i.e.: longitudinal and transversal folds and thicker cuticular ridges, material aggregates around the buccal capsule and/or vulva or anus). The main changes concerned the cuticle and the buccal area. The structural changes found in the worms exposed to TR plants might affect their motility and nutrition with possible consequences on their reproduction, as suggested by previous in vivo trials.