Studies using Teladorsagia circumcincta in an in vitro direct challenge method using abomasal tissue explants.

An in vitro direct challenge (IVDC) method in which abomasal tissue explants maintained at 37 degrees C in Hanks/Hepes solution (pH 7.6) in a high oxygen concentration (incubator gassed with pure oxygen and sealed prior to use) were-challenged with exsheathed third stage larvae of Teladorsagia circumcincta has been used to investigate the tissue association phase of larval establishment. Studies using naïve and recently challenged immune sheep and goat abomasal tissues have shown significant reductions (P < 0.05) in the numbers of tissue associated larvae in material from immune animals. The mechanisms that affect the tissue association process appear to be labile since more larvae were recovered from the tissue digests of previously infected sheep that had not been recently exposed to larval challenge in comparison to those that had been recently challenged (P < 0.05). The method has also been used to demonstrate the influence of protein nutrition on the establishment of larvae in abomasal tissues and region specific differences in the efficacy of exclusion mechanisms. The technique appears to have potential as a means of investigating the crucial first phase of the process of establishment.