Activation associated secreted proteins (ASP) are members of a nematode-specific protein family belonging to the SCP/Tpx-1/Ag5/ PR-1/Sc7 family. Three different types of molecules have been identified in this family: two-domain ASPs and single-domain ASPs showing homology to either the C-terminal or N-terminal domain of the two-domain ASP. The function of these proteins is still unclear, but a role in transition to parasitism and a role as allergen are often suggested. Here we report that the abomasal cattle parasite Ostertagia ostertagi produces at least 15 ASPs, including two-domain and C-and N-type single-domain ASPs. Ten of these are highly transcribed in the L4 stage, whereas others are highly enriched in adult male worms. The latter was especially the case for the N-type single-domain ASPs Oo-ASP1 and Oo-ASP2 and also for Oo-ASP3, which is homologous with the Haemonchus contortus and Ancylostoma caninum Ctype single-domain ASPs. Immunohistochemistry showed that Oo-ASP3 was localised in the oesophagus. Oo-ASP1 and Oo-ASP2 on the other hand were localised in the reproductive tract of both male and female worms, suggesting a role in reproduction or in the development of the reproductive tract. Ó

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Recent reports of suspected ivermectin (IVM) resistance in Ostertagia ostertagi have highlighted the need for research into the mechanisms of IVM resistance. However, there are no reports of resistant field isolates of O. ostertagi, which have been characterized for molecular research. Therefore, an anthelmintic susceptible O. ostertagi population was selected for IVM resistance by repeatedly exposing the population to subtherapeutic and therapeutic levels of IVM over 10 generations. In each selection round, a group of calves was infected with the progeny of the previous IVM-selected O. ostertagi population. In the last selection round a therapeutic IVM dose (0.2 mg/kg BW) only reduced the faecal egg counts by 57% and 65% on days 7 and 14 after treatment, respectively. In contrast, the therapeutic IVM dose was 100% effective at eliminating the parental IVM-susceptible isolate. #